Rack and Pinion Steering

Well in my search to fit power assisted rack and pinion to my buggy I have learnt a lot about the subject. I did the reading and I bought the books... came up with my design and though all was pretty cool.

Then I found thsi picture of someone who has done it ......

Seems to me if thsi works then I have wasted many hours of my life ....

Hi

That looks like a Camira rack.

1302Steve

Not being rude but WTF. Go the bump steer

Bump steer and I reckon the 30" tyres he has on the front will hit his rack ends.

It is teh best pic I could find of one actually setup.

Anyone got any better ones ? I an not putting my rack in this position but would like info from anyone out there who is running rack and pinion if possible.

That set-up would have less bump steer than the original steering box. Having the tie-rods as long as possible is a good thing.

It looks like it was power steering but is bypassing to itself. LHD so not Camira.

Baja Wes wrote:That set-up would have less bump steer than the original steering box. Having the tie-rods as long as possible is a good thing.

Hmmm, I won't say you are wrong, but I'm not sure I agree.

The suspension pivots at the torsion bars, for the steering to have no bump steer the steering should pivot at the same point. Ie. as close to the torsion bars as possible.

The setup pictured (and the one on the green buggy) both have steering that pivots further away from the torsion bars then the stock setup.

The best place to have the steering pivot would be right up the front at the torsion bars (where the adjusters get welded)

The rack used in the picture above, if moved right forward, would work well due to the long steering arms.

The rack and pinion shown on the webpage below would work well as it is mounted up on the torsion bars. This would make it better than the stock as it would totally eliminate bump steer.

http://www.chirco.com/projectbaja/baja_10.htm

I've done up this diagram to try and give everyone a bit more of an understanding of steering geometry and to try to explain why the rack and pinion setup shown will give significant bump steer.

This is a difficult topic to get your head around so if I don't explain it in a suitable way let me know and I will try and elaborate.

There are two triangles on the picture (A & B). Triangle B shows the geometry of the suspension and I will explain it's relevance first. Triangle A shows the geometry of the rack and pinion setup.

Triangle B
The beetle torsion bar suspension pivots along the torsion tubes (blue line). The torsion arms (yellow line) are a solid and run on bushes in the torsion bar. Therefore their geometry to the blue line cannot change. The point where the torsion arms attach to the steering knuckle travels up and down in an arc at 90 degrees relative to the torsion tubes. So as the suspension goes up or down the point where the red and yellow line meet gets closer to and further away from the front of the car but it's distance from the torsion tube does not change (the torsion arm is a solid object). Now if you imagine the triangle (B) to be a solid object you could take the point where the yellow and red lines meet and spin it around and around the torsion bar and the length of all three sides of the triangle would remain the same. IE. in real life you can spin a torsion arm around and around the torsion tube when there is no steering knuckle or torsion bars in the torsion tube.

Triangle A
Triangle A shows the geometry of the rack and pinion steering in this car. The yellow line is again the torsion arm, the blue line is the static line or pivot line of the steering, and the red line represents the tie rod. The first sign that this setup is not geometrically correct is that the blue pivot line is nowhere near the same location as the pivot line of the front suspension (Blue line triangle B). As a wheel travels through it's movement the torsion arm (yellow line) will pivot on it's arc around the torsion tube. As it moves up and forward the distance between where is meets the steering knuckle (yellow meets red) and the centre of the rack (blue meets red) needs to increase. Since the tie rod is a static object and cannot increase, the steering is pulled inward and therefore the front of the tyre will move outward. Bump steer.

The best geometry for steering is to be exactly the same as the geometry of the suspension. The geometry of the suspension is triangle B, so we need to make the geometry of the steering as close as possible to triangle B to eliminate bump steer. This could be achieved by having a rack and pinion setup mounted right up on the front torsion tube with it's tie rods pivoting where the red and blue line meet on triangle B.

If the rack pictured was moved all the way forward, flipped end to end, mounted on the torsion tubes, and had the tie rod mounts attached to the back (instead of the front) it would work well. Looking at the rack, the centre section may well be free to rotate and could be rolled over so the tie rods attached to the back.

Hopefully I've explained that correctly.

[Edited on 4-6-2004 by MikeM]

I sent the picture of the rack to my cousin who owns a power steering and transmission shop.

He said that the rack is very similar to the racks used on Camiras and some Audis. But obvisously Camiras and the Local market Audis have a RHD version.

The center section cannot be modified to mount the tie rods on the other side (back) as the center section on the Camira racks is cast alloy. What could potentially be done though is a piece of u chanel could be mounted over the center section to bolt onto the stock mount on the front but allow the tie rods to be bolted to the back. We'd have to confirm with a blue plate officer whether this would be acceptable.

This rack would be dead easy to mount on the front torsion tubes, it just depends whether we can come up with a way to mount the tie rods to the back and get it all approved.

Also my cousin mentioned that the shortest available standard rack (end mount not center) is actually a standard Commodore rack. These are around 20 inches long. Due to the number of varieties of commodores over the years the tie rods are available is many custom lengths so getting it the right overall length for the VW should be easy enough. I will look into this option a bit more as he has several commodore racks sitting in his workshop at the moment.

[Edited on 4-6-2004 by MikeM]

I never said it's good. Just probably better than stock.

Sure as it travels each wheel will toe out, be it will be even amounts.

The stock set-up weaves on big bumps cos the short tie rod and long tie rod are changing the toe different amounts on each side, causing it to make the car want to turn on big bumps.

If you have (and I know you will) a copy of Jeff Hiddard's book baja bugs and buggies, have a look at page 66. In a box on the left All about bump steer I use this when I set up a car with howe or wright racks and have on prob's. maybe It can help you to..

Baja Wes wrote:I never said it's good. Just probably better than stock.

Sure as it travels each wheel will toe out, be it will be even amounts.

The stock set-up weaves on big bumps cos the short tie rod and long tie rod are changing the toe different amounts on each side, causing it to make the car want to turn on big bumps.

I agree with that. The toe in and toe out change with this rack would be signifigantly more than stock, but at least it would be even side to side. So the bump steer would be less than stock, but the toe in toe out changes would be greater.

Unless of course one wheel was up and the other side was near neutral. Then one side would have more toe out than the other causing bump steer.

🙂

[Edited on 4-6-2004 by MikeM]

one more thing ????? while talking steering geometry. how do you guys go with the ackermans angle on your short wheel base Buggies

Desert Moose wrote:one more thing ????? while talking steering geometry. how do you guys go with the ackermans angle on your short wheel base Buggies

Hehe, yeah, they're not right. The tyres squel like mad when on a painted surface like a car park etc as they are not right. Not such and issue when offroad though.

something to look into if your making front stubs but

MikeM wrote:[
The best geometry for steering is to be exactly the same as the geometry of the suspension. The geometry of the suspension is triangle B, so we need to make the geometry of the steering as close as possible to triangle B to eliminate bump steer. This could be achieved by having a rack and pinion setup mounted right up on the front torsion tube with it's tie rods pivoting where the red and blue line meet on triangle B.

.

The best geometry for eliminating bump steer - YES.
The best geometry for steering -NO because the ackerman will be wrong.

The best compromise would probably put the inner ends of the tie rods about the same distance behind the front beam as standard, assuming the VW steering was optimum on the original and that the track and wheelbase was unaltered.

In the case of a shortened wheelbase, moving it back or forward could be used to correct the ackerman error (possibly at the expense of bump steer).

The bump steer characteristic would also be affected by any other changes to the front suspension such as raising or lowering.





[Edited on 4-6-2004 by lexm]

I see Bump steer as a much bigger issue than Ackerman. As long as the Ackerman angles are close to stock (which they would be with the rack mounted on the torsion tube or just behind) I don't think it would be a concern.

http://www.auto-ware.com/setup/ack_rac.htm

Here is a cool reference on car handling. Actually relates to RC model cars, but hey a Manx is just a big toy car 🙂

http://rctek.com/handling/index.html

This is pretty cool, gives some info on how Ackerman can be set.

http://rctek.com/handling/ackerman_steering_principle.html

This is actually a bit simplistic as it does not take into concern the arc travelled by the pitman arm or the steering knuckle.

Having now read a bit of info on Ackerman I believe that putting a rack and pinion on the humble VW may actually fix the Ackerman rather than make it worse. Is the Ackerman on a VW actually correct? It will be at one point, but probably not at all points due to the swing of the pitman and the issues with a short and long tie rod. At full lock I'd say a VW has incorrect Ackerman.

If I get enthusiastic I will look into this more. There must be some equations relating to this somewhere.

[Edited on 4-6-2004 by MikeM]

love this stuff

mmm looks like some people have gone and gotten some big words........ hehe

If all goes to plan I should have a Power assisted R & P on a ball joint front end in the next few weeks. Just sorting out exactly what the engineer wants before he will approve it.

The above does make for very interesting reading though... so where are all your pics of setups though ??

Cool

What's that going on Brad? Last I checked the Mega manx was using Link Pin?

the center mount race rack no good Brad .I know where there is two of them .Not power but very good $$ :alien

Buggy Brad wrote:so where are all your pics of setups though ??

G'day Brad
No pic's now but I will have some for ya soon. I use a S.O.R.E rack, non power (like a wright rack) which is center mounted and a power steering servo out of a forklift up near the S/wheel. the pump runs off the crank with a small pulley and a type III bolt. the pump came from Kartek in the U.S. with the mount for Type 1 motor (3 nuts on the alt stand and one case stud)

This is the pump its not the best pic but I will replace it later with a better one and also one of the rack and servo..

Buggy Brad wrote:😎

Ahh, the ever mysterious Brad.

Well when you get it approved can you give us a brief run down on what the engineer required to get it past? I am interested in running a Rack and Pinion in the SubaManx so I'm curious as to the engineers requirements.

Mike.



[Edited on 7-6-2004 by MikeM]

now that's a steering damper!

FWIW that first picture IS using the same rack setup as Camira. Remember Camira is an Opel and was sold all round the world as the GM "J" car, so you can do the same setup here using the camira rack. JD and JE were available with power steering.

Hey Mike, I know where you got that photo you posted...... lol

the Wright place

A fellow Eureka owner has used a R & P out of a Hyundai not sure on how legal it is but I'll see if I can get pics.

There was an old 1980's vintage article on R & P steering for VW based kit cars. Go to the Nova site here

http://www.nova-international.net/home.htm

then on the left bar click ‘data’ when the page loads, scroll down the Right hand side and click ‘The chassis’ then when that loads scroll down to "an alternative steering system to the VW"

Jenny wrote:http://www.nova-international.net/home.htm

then on the left bar click ‘data’ when the page loads, scroll down the Right hand side and click ‘The chassis’ then when that loads scroll down to "an alternative steering system to the VW"

I just looked at that. That guy has no idea what he is doing, and his set-up sucks. Problem is he is thinking 2D, not 3D. The susp arms actually swing in an arc out of the page of his pic. macpherson strut susp design doesn't work on torsion bars.

I've been running some calcs for Brad. I have found the stock set-up can get nearly no bump steer at all if set-up absolutely precisely accurately perfect. The problem is this is very unlikely to occur in the real world. error's in exact steering box angle, eccentric camber adjustments and other things eventually lead to the stock set-up being prone to bump steer.

Hey Brad I don't know if this will help you but a long time ago when I was fitting racks I made a toe beam. What’s this you ask, it one step up from a tape measure...lol. I got a 25mm piece of Polly pipe 6" short of the inside of both front tyres (about 1100mm long) then a 12” bit of broom stick and a 24mm spring that was about 10” long. Drill a hole in the stick 2” away from the end and put a bolt though it. But the broom stick in the pipe with the spring between the bolt and the pipe. On the broom stick at about 5” and up to 7” mark it off in millimeters this is where you read your toe change. Take you torsion bars out and use a jack to lift and lower the front of the car to check the bump steer. With the rack tacked you can move the rack up, down, back or forward to get the right bump steer before you weld it. This cool backyard tool can be used as a bodgie wheel aligner as well. When the car is back together but it at the front of the wheels then roll the car forward till the toe beam is at the same height at the back this will give you your total toe reading e.g. the difference between the to reading. Bodgie but it works. (I use a laser aligner now to setup but it takes longer).

Moose
:thumb

Desert Moose wrote:This cool backyard tool can be used as a bodgie wheel aligner as well. When the car is back together but it at the front of the wheels then roll the car forward till the toe beam is at the same height at the back this will give you your total toe reading e.g. the difference between the to reading. Bodgie but it works. (I use a laser aligner now to setup but it takes longer).

I use a similar method to do my wheel alignments, and I find it works fine. 🙂

The prob with taking it to a wheel alignment shop is that the next time you go offroad it seems to move slightly and go out of whack anyway. 🙁

I am currently trying to get accurate measurements of the geometry of the stock beam. It's very hard to do actually!

Once I have that sorted I will know exactly what toe and bump steer probs the stock set-up has. Earlier measurements indicate it has some weird built in bump steer on purpose. I'm not sure why yet, which generally means I am missing something. I'm sure I will figure it out. It's related to the non-symmetric pitman arm.

MikeM wrote:The best place to have the steering pivot would be right up the front at the torsion bars (where the adjusters get welded)

Just flicking through this post again. Thought I'd clarify this one. The best position for the rack is imaginary posts that are offset from the centerline of the top torsion tube, the exactly same amount that the steering arm tie-tod center is offset from the top arm ball joint center.

So that is up and back a certain amount. From rough measurements it's about 60mm up, and 110mm back.

The stock pitman arm tie rod end centerpoints are very close to this offset, so the stock set-up comes very close to eliminating bump steer. The prob is the left and right pitman arms tie rod ends are different offsets from the beam, I haven't quite put my finger on why.

I thought the left and right steering arms on the spindles may have had different offsets, but they don't seem to have. I'll keep thinking. Once I have the 3D model working it will make it fairly obvious why I think.

Here's my rough spreadsheet if anyone is interested. It is a simple first past calc of bump steer vs susp travel. It is ignoring the wheels turning left or right, camber adjustments and any difference in length of the top and bottom arms.

Desert moose, the idea of fine tuning the exact rack placement is a good one. A lot of race cars actually fit the rack, measure the bump steer and then use shims for fine tuning. Sometime they dial in very very small amounts of toe in or toe out bump steer to change handling characteristics.

Baja Wes wrote:

MikeM wrote:The best place to have the steering pivot would be right up the front at the torsion bars (where the adjusters get welded)

Just flicking through this post again. Thought I'd clarify this one. The best position for the rack is imaginary posts that are offset from the centerline of the top torsion tube, the exactly same amount that the steering arm tie-tod center is offset from the top arm ball joint center.

To maintain ackerman - yes.
To eliminate bump steer - no. The rack would have to be in or very close to the plane of the torsion tubes. But some bump steer may be desirable as you say.

The prob is the left and right pitman arms tie rod ends are different offsets from the beam, I haven't quite put my finger on why.

So the ackerman is similar on both sides with different length tie rods.

[Edited on 27-6-2004 by lexm]

isnt the ackerman affected by the poistioning of the tierod end on the spindle, not by where the steering box is mounted???

dak dak ute wrote:isnt the ackerman affected by the poistioning of the tierod end on the spindle, not by where the steering box is mounted???

In an ideal situation it would be set by the relative position of the outer tie rod end to the king pin position (or in ball joints the pivot position which is a line through the ball joints) as long as the pitman arms moves in an arc the same radius as the distance from the outer tie rod to the King pin axis. The raplacement of a radially moving pitman arm with a linear moving rack end will modify the ackerman calculations, as will the change of length of the tie rods.

lexm wrote:To eliminate bump steer - no. The rack would have to be in or very close to the plane of the torsion tubes. But some bump steer may be desirable as you say.

No, if you mount it in the plane of the torsion tube, you will get bump steer. The arms pivot at the torsion tube, and swing an arc from there. But the arc the tie-rod end on the spindle does is offset from that arc by the distance from the top ball joint to the tie rod end. You want the rack to be at the center of that second arc. So you want the rack offset from the torsion tube centerline the same amount that the tie rod end is offset from the top ball joint. I've ran the calc's and this is definitely correct.

You may be right about the pitman arm having more to do with the ackerman. I haven't ran these calcs yet, but when I do it will show whether that is the case of not. If it is the case then VW have purposely given the car bump steer in order to keep the ackerman correct. The ackerman on the spindles seems to be correct from the factory, with the line from the ball joint to tie rod end to center of rear axle in one plane.

If the pitman arm is like that due to ackerman, then it means VW should have went with an idler pitman arm set-up to make the two side symmetric and eliminate the bump steer problem, but I guess it was intented to be a cheap car.

all very interesting really :alien

Buggy Brad wrote:all very interesting really

LOL....yeh, that it is.

Something to think about when you do you calculations Wes is Caster, that’s if you haven’t already. The caster effects camber and toe on turns which effects Ackerman’s.
It’s all getting to hard and my head hurts :cry

yeah I got castor covered. Castor and Camber are adjustable with the eccentric adjuster, just to make the calculations more difficult. Just look at the excel sheet that does a simplified calculation and you'll get an idea how complex it gets real quick.

The compound effects of the various angles and adjustments makes everything more complex. I mean you can even set the long tie rod a little longer, short one a little shorter, and end up with the pitman arm slightly turned with the wheels straight ahead. This also has a slight effect on the geometry (but it won't have an effect with a steering rack).

Building it is easier, cos you just fine tune the position from trial and error as you said. But to make it legal we need to prove through calculations that it's equal to or better than the stock set-up :o

Baja Wes wrote:But to make it legal we need to prove through calculations that it's equal to or better than the stock set-up :o

I think even with bump a rack will be better then stock.....lol
I didn't see the excel doc before ! looks like a lot of work to prove your case but I'm sure you will.

the excel sheet is an attachment to a post about 9 posts up this page. 41kB or so. Just click the link and it will open in Excel. If you have Excel I guess.

It will look kinda like this when you open it...

lot of work .... lucky he gets paid by the hour 😎

Baja Wes wrote:

lexm wrote:To eliminate bump steer - no. The rack would have to be in or very close to the plane of the torsion tubes. But some bump steer may be desirable as you say.

No, if you mount it in the plane of the torsion tube, you will get bump steer. The arms pivot at the torsion tube, and swing an arc from there. But the arc the tie-rod end on the spindle does is offset from that arc by the distance from the top ball joint to the tie rod end. You want the rack to be at the center of that second arc. So you want the rack offset from the torsion tube centerline the same amount that the tie rod end is offset from the top ball joint. I've ran the calc's and this is definitely correct..

Quite correct. I neglected that. When are you going to expand the spreadsheet for different steering angles. Should be interesting as the effective length of the pitman arm will reduce as it rotates, as will the tierodend-balljoint on the inner wheel but increase on the outer wheel, all by different amounts. 🙂🙂

Interesting to see how a small change affects the bump steer. I believe the distance between upper and lower ball joints is different to distance between torsion bars, so this would also affect the calculations.



[Edited on 29-6-2004 by lexm]

quite right with everything there lexm.

I have started measuring everything, as that is the first step.

I have decided that an Excel sheet to calculate it will be incredibly complex, and even if I made it I would have trouble getting someone to believe it without some seriously detailed checking.

I am currently planning to use some advanced 3D motion software. Basically I draw the front end, add spherical constraint for ball joints, pin constraints at the beam, and simulate the motion of the front suspension. The program can output graphs of positions and angle of rotations of various parts through the movement. It will all make sense when I post some pics up here. 😀

here is a pic of my first rough model of the front end made up of cylinders and spheres, it basically picks up the mainly workpoints of the front end which is all you need to animate the movements properly.

hehe must be a stock front end with those stub axles :>

Baja Wes wrote:here is a pic of my first rough model of the front end made up of cylinders and spheres, it basically picks up the mainly workpoints of the front end which is all you need to animate the movements properly.

It's not moving :thumb:thumb:thumb:thumb

gotta finish the non-moving front end before I get the movement sorted.

I'll tell you what, measuring the workpoints of the front end accurately is extremely difficult. It's hard to measure from the center to center distance of a ball joint, without cutting it in half to know where the center is!

From what I can measure, I think both arms might be 153mm long. (very hard to measure). Long in a perpendicular to the beam direction, not total length.

The center to center width of the top ball joints appear to be 1170mm, and the bottom ones are a little wider at 1205mm.

The pitman arm appears to be sweeping up at 59-60 degrees.

My head hurts 🙁

Anyway, here is a front beam, shock tower not drawn yet (they are trickier to draw, and not need for the calcs).

[Edited on 6-7-2004 by Baja Wes]

Cool...... very cool.....

I have a couple of balls from stuffed balljoints that are out of their sockets. These would easy to measure with some callipers. I'll post my measurements on here tonight (or Saturday) so you have something to compare against if you like. I will measure the diameter of the ball, the overall length of the ball and mounting bolt, and the length of the bolt sticking out of the ball.

I'd like to do this for a Link Pin beam as well. For Completeness (nothing to do with the fact that both my cars are link pin 🙂 ) If I can do the measurements can you model it for me? The Link Pin front end should model the same as the ball joint if we change the measurements.

The fact that there is 4 pivot points for a link pin assembly won't matter as we can still model these as two if we place the center of the link pin pivot in the same X plane as the Kinpin. That will model just like the Ball joint but still be accurate for link pin.

the problem isn't drawing the ball joints themselves, as I don't need to draw them. It's getting a ruler or calipers, sticking it near a beam and trying to actuall measure things like the height from the top ball joint center to the bottom ball joint center. It is tricky to figure out where the hell the center accurately is. Try it and you'll see what I mean 🙂

The link pin front would be easier. you can see where the pins are, and where their axes are. The program will model the link and king pins are pin restraints quite well.

Wes will this help

That rack in the ealier picture is also similar of some SAAB racs, though being a GM subsidary I would expect it.

Bloody hell Wes, I think you've got too much time on your hands!!! Awesome job though, as usual! :thumb

Desert Moose wrote:Wes will this help

no, but it does look cool 😀

I AGREE WITH MOST OF WHATS BEEN SAID!!!!

Except the bit after.....

Quote:Buggy Brad
"Rack and Pinion Steering

Seems to me if thsi works then I have wasted many hours of my life .... "

After that you lost me.

It will work... Wes isn't paid to fail ... :kiss

just to let people know, I am still at it...

the ackerman angle is showing the desired effect, and the stock front is showing bumpsteer. I still think I need more accurate measurements though...

Oh, and most parts are simply diagramatic with the correct workpoints though.

for those following the story...

assuming the front arms were equal length, and always at the same angle, then putting the rack at the same offset as the tie rod to top ball joint center would be perfect and give no bump steer.

Unfortunately reality is more complicated. Even if the arms are the same length (not 100% sure yet, but seem the same), the problem is that the spacing of the top and bottom ball joint is bigger than the spacing of the torsion tubes. So what it means is the top and bottom arm are on different angles.

This is a problem because as the arms swing through their travel, they change the forward to back tilt of the wheel spindle. So the effective back and up distance of the tie rod end to the top ball joint actually changes the whole way through the travel. So it is impossible to design a rack with no bump steer. the stock set-up will also suffer from this.

So basically there is an avoidable amount of bump steer (unless you cut the beam and space the torsion tubes another 20mm apart to match the ball joints).

The question then becomes, how do we reduce the bump steer so that it is less then stock. Well I guess we are back to a center mount rack like on the camira. 🙂

Moose, when you setting your racks up, can you ever completely eliminate the bump steer, or do you always have a little bit?

Hmmmm. Interesting. Nice work.

As the suspension travels from total down to total up the outer tie rod end travels through an arc. If this arc was constant it would form a circle and the center of that circle is where the inner tie rod end should be (if we are thinking front to rear and up and down).

I'm guessing the issue is that the arc travelled by the outer tie rod, if continued, would form an oval. This give us no point that is a constant distance from the outer tie rod at all positions of travel (the center of a circle).

Therefore there is no perfect spot for the inner tie rod end, it must be a compromise.

My gut feeling then is to aim for a point at the mid-point of suspension travel and set the tie rod end at that point. I'm thinking this can be found easiest with our earlier theory of 60 up 110 back, but scaled. In an exaggerated example lets assume a few things. The Torsion bars are 50mm apart and the ball joints are 100mm apart. That would mean the scale from ball joints to torsion bars is 50/100. If the outer tie rod is 60mm above the upper ball joint the inner tie rod should be 0.5 * 60 or 30mm above the upper torsion bar. The back distance (110mm) stays the same.

This is just a theory in my head but it seems sound. You'd have to model it to be sure. :duh

Mike,

We think alike. Yes I thought maybe it moved in a new arc, but yes I also thought it'd probably actually move in an ellipse and therefore not actually have a fixed center.

But instead of attempting calc's I decided to draw it. It's very complicated this steering business, especially considering traditional steering theory doesn't apply to the VW torsion bar front end. I like to thoroughly calculate everything before I comment, but this post is an exception where I am saying what I am thinking while calculating so that forum members can make sure my thoughts are on the right track. Anyway, back to the R&P.

So I drew a simple 2D drawing of the side on view. I then rotated the lower arm in 20 degree increments. I then relinked and rotated the spindle, top arm and tie rod end point for each 20 degree rotation. So what we end up with is 5 different colours, showing the front end in 5 different positions through the travel. Hopefully the drawing makes sense. The two circles are the torsion tubes, a line for top and bottom arms, a line for the spindle axis, a line for the spindle to tie rod end attachment point.

From looking at it something else becomes obvious. The castor angle changes through the suspension travel. Good positive castor when the suspension is raised, and bad negative castor when the suspension is lowered.

This is interested because we all know that when you lower a beetle it loses castor and you need to fit castor shims to correct the problem. But the explanation I always saw was that tilting the whole pan by lowering the front tilted the beam and this caused the problem. Which I though was silly cos you normally lower the front and the back. From the drawing, we actually see we need castor shims because of the arm geometry. Because of the different spacing of the torsion bars and the upper & lower ball joints. Why did VW do that anyway....

Baja Wes wrote:for those following the story...

assuming the front arms were equal length, and always at the same angle, then putting the rack at the same offset as the tie rod to top ball joint center would be perfect and give no bump steer.

Unfortunately reality is more complicated. Even if the arms are the same length (not 100% sure yet, but seem the same), the problem is that the spacing of the top and bottom ball joint is bigger than the spacing of the torsion tubes. So what it means is the top and bottom arm are on different angles.

This is a problem because as the arms swing through their travel, they change the forward to back tilt of the wheel spindle. So the effective back and up distance of the tie rod end to the top ball joint actually changes the whole way through the travel. So it is impossible to design a rack with no bump steer. the stock set-up will also suffer from this.

So basically there is an avoidable amount of bump steer (unless you cut the beam and space the torsion tubes another 20mm apart to match the ball joints).

The question then becomes, how do we reduce the bump steer so that it is less then stock. Well I guess we are back to a center mount rack like on the camira. 🙂

Moose, when you setting your racks up, can you ever completely eliminate the bump steer, or do you always have a little bit?

Well, firstly let me say what a wonderful job you have done on this.
I have never set up a ball joint front, all the cars I do are link pin type and there is little if any difference between the link pins and the beam. The other thing is the beams are much longer (1275mm) and set at 14deg. As for bump yes and no, from ride height about 3” up and down I get +/-1mm at the most. But max travel (bump stop) it always + about 2mm but full extension (in the air) it would be –1mm at the most. Please remember that there is nothing on the front end of these cars that’s VW and there run from 15” to 18” of travel.
So the long and short of it NO I don’t get bump steer (I don’t think -/+ 3 over 15” is a problem but it is still bump steer.
:duh

but back to the rack and pinion again 😀

So the question is.... does the tie rod point swing an circular arc or an elliptical arc?

well...


the answer is....


a circular arc!

How convenient. So maybe we won't need a Camira rack. The back and up point is completely different. It's a smaller back distance than the tie-rod to BJ back distance at any point. I know what it is and will stick it in my 3D model tonight, reanimate the suspension and see if it cures the bump steer. It should of course, unless I am missing something, again... :P

Desert Moose wrote:The other thing is the beams are much longer (1275mm) and set at 14deg.

14 degrees, wow, that's some serious castor!

Thanks Moose. The rack model was getting more bump steer than that, like about 11mm per wheel! Looks like I figured out why in the above posts. 😀

But I still have to set each car up different as no to are the same. I will post some photo's of mounts I have made plus I'm about to do one soon and I'll make sure I take pic's for you.:thumb

Baja Wes wrote:So the question is.... does the tie rod point swing an circular arc or an elliptical arc?

well...

the answer is....

a circular arc!

Cool!

:bounce :bounce :thumb

That should make it easier.

[Edited on 6-7-2004 by MikeM]

Baja Wes wrote:14 degrees, wow, that's some serious castor!

😀

Yeh, lol. looks like a grader on lock :P

But it will center on a dirt road at 200kmh

[Edited on 6-7-2004 by Desert Moose]

Baja Wes wrote:... Because of the different spacing of the torsion bars and the upper & lower ball joints. Why did VW do that anyway....

I just thought of another side effect caused by that and the spindle changing angle. The ackerman angle will change through-out the suspension travel too!

Either VW did something really weird for no reason, or we're all really missing something...

in one manual i have, factory was toe in, and as you come through changes the steering to toe out to allow fo the different arcs each wheel has to follow

alos are you taking in to account that the torsion tubes arent dirrectly above and below each other... bottom one is slightly forward

(this is according to volkswagen technical manual by henry elfrink)

dak dak ute wrote:alos are you taking in to account that the torsion tubes arent dirrectly above and below each other... bottom one is slightly forward

(this is according to volkswagen technical manual by henry elfrink)

I think he is Dak Dak U thats what Castor of the beam is :thumb

okay cool just checking

I'm not taking account of the tilt of the beam, mainly because it has no effect on where the beam has bump steer or not. If the beam is on an angle of 0 or 5 degrees tilt it won't matter as the steering box or rack is mounted to the beam. does that make sense?

modelling it vertical is a little easier.

So anyway, I re-ran the model and I have found a position for the rack which give no bump steer at all, and the length of the tie-rods or whether the rack is center-mount or not has absolutely no effect. I will post a pretty pic in a minute...

here's a pretty pic, looks similar to before but with the rack in a slightly different spot.

The measurements still aren't 100% accurate, but I am convinced that any changes in measurements will simply mean a slight relocation of the rack, and importantly still no bump steer.

Now of course the racer boy's already know this, but I can prove it so I can get it legal. 😀

So let me explain what I've done for those who are interested.

I model the front suspension in a fancy 3D motion program. First I draw the suspension in 3D of course. Once drawn I still local co-ordinates onto the parts (the little red bits). I then join the various parts at those local co-ordinates using various constraints.

Constraints range from spherical constraints (ball joints etc), and pin constraints (the arms in the beam), and sliding constraints (like the steering rack moving rack), etc.

Then I can put controls on various constraints as well. So I have put slider controls on both upper arms, which lets me move the arms by moving the slider. There are 3 sliders in the screenshot. The last one is the rack position, so I can turn the wheels too.

The program uses interation to calculate movements, forces, velocites, accelerations, etc. Very computer intensive.

So I can also graph practically anything. I have graphed the rotation of the left and right wheels (in a steering sense of rotation). I ran the model, moved one arm through it's travel, then the other through it's travel, and the graph recorded the bump steer. It recorded a max bumpsteer of 0.07 degrees, which ends end less than 0.5mm at the edge of the wheel. So within the tolerance of what I've drawn and the accuracy setting I have the program at.

so as a comparison, here is the stock front end, charted the same.

The rough curve is because I wasn't very steady moving the slider with my mouse 🙂

You can see the short tie rod gets about 1.7degrees of bump steer (about 10mm at the front of the wheel!), but the long tie-rod is much less effected. These bump steer figures may also be because I haven't measured the exactly location of the pitman arm exact enough. But it's clear at least one tie rod on the stock set-up will always have bump steer due to the unsymmetric pitman arm.

here's a quick avi

www.offroadvw.net/rack.avi

I think you'll need the DivX codec from somewhere...

Actually ignore the avi above, I made a much better one. Only 768kB

http://www.offroadvw.net/rack2.avi

I'll find a link to the DivX codec

Go here...
http://public.planetmirror.com/pub/divx/windows/

and download the DivX505Bundle.exe file.

Install DivX

Open the movies above in the DivX player.

There are DivX codex for windows media player out there, but I can't find it right now.

Wes, can you make the tie rods longer as in 100mm apart in the centre, :thumb

I can, but it won't do anything any different than what the short tie-rod rack design is doing. Although it didn't look like it at first, any rack can be set-up for theoretically 0 bump steer.

Long tie-rod versions will just be less sensitive to how accurately it is initially set-up than short tie-rod versions. But they will both be equal is they are both set-up perfectly.

Baja Wes wrote:Although it didn't look like it at first, any rack can be set-up for theoretically 0 bump steer.

True, but there are other things to consider. The centre tie rod rack (Camira) has an advantage in that the angle changes in the up and down plane are less as the suspension travels. I have done a diagram. It's not as cool as Wes's diagrams, but I don't have the cool tools he has.

In the diagram you can see the Two black lines are the torsion bars viewed from the front (or rear) the red objects are the spindles and the blue lines are tie rods. Points A are the inner mounts of the tie rods on a long rack, points B are the inner tie rods on a Camira style rack, and points C are the outer tie rod mounts.

You can the the difference in angle in the tie rods for both scenarios. The center pivot rack has much less angle, especially on the right side where the suspension is dropped further.

Less angle is a good thing as it puts less upward or downward pressure on the tie rod ends, and is less likely to bend tie rods. It will also mean the tie rods ends have more serviceable life as they are not moving as much.

I think the Ackerman angle is effected by the angle to the inner tie rod (front to rear) when viewed from the top. But I don't see this as a huge concern.

[Edited on 7-7-2004 by MikeM]

yes longer tie-rods will not swivel as great an angle.

However longer tie-rods need to be made stronger to resist buckling, which isn't such a prob with shorter tie-rods. It's easy to fix by just making beefier tie-rods though.

I'm going to try to update my spreadsheet that I started. I want it to calculate everything the 3D model does. That way you can easily move the rack around in excel and see what the effect is. At the moment the rack at the start of this post is looking pretty damn bad, and I would like to calc it just out of interest.

Calculating all the angles in Excel is a very intense process :O

Just to relate the angle that the bottom arm is compared to the top arm is complicated and looks something like this "=90-(DEGREES(ATAN(D30/(150+C30)))+DEGREES(ACOS((L_armlower^2+((C30+150)^2+D30^2)-H_balls^2)/(2*SQRT((C30+150)^2+D30^2)*L_armlower))))"

I knew trigonometry would come in handy one day 😀

I finished work and decided to run some quick numbers on the rack set-up shown in Brad's very first post.

I reckon the rack position looks like it is dead in between the tie rod ends, and maybe an inch above the centerline of the beam. Running the calc's on that set-up is giving me about 50mm per wheel of toe change! (25mm at best)

I didn't realise it was that bad. It would certainly suck to drive. 😀

[Edited on 7-7-2004 by Baja Wes]

50mm :duh nasty ....

Baja Wes wrote:yes longer tie-rods will not swivel as great an angle.

However longer tie-rods need to be made stronger to resist buckling, which isn't such a prob with shorter tie-rods. It's easy to fix by just making beefier tie-rods though.

😀

Wes,For tie rods I use heim's with adapters and C/molly tube, or 3/4" alloy bar, gun drilled to 5/8". Much stronger than standard and I'm not sure but you could take the material spec sheet to the governing body when you take everything else.

I know this started as brad's thread but I think the world is looking in on what you are doing Wes........lol (I have had 8 u2u's about it, god know how many your gettin').
I really like the way you are putting in such an effort to make this work.


This photo I have put on as a URL so I don’t take up much room on the thread but I have had a lot of people ask about it so here is a pic.
http://img78.photobucket.com/albums/v252/Moose906/7.jpg

So I modelled the center rack, at the rear (same as first pic).

I played with the Excel sheet to get it in the back spot, but still near the firewall like the pic shows. The Excel sheet was giving around 29mm of toe change per wheel.

Then once modelled the model gave 5 degree change per wheel, which ends up equalling about 29mm toe change per wheel. So that's a nice check of both methods, it's good they agree.

and a prettier pic...

I decided to run a sensitivity analysis on the rack position, for a normal rack and a camira center mount rack.

So basically what I done is calculated the bump steer with the rack in the perfect spot (or close enough to get less than 1mm of bump steer). I then moved the rack up 5mm and recorded the bump steer, down 5mm and done the same, then back 5mm and forward 5mm. I put it in the table below.

I did it twice, only with a normal rack, about 600mm wide, and once with the camira rack, with what I guessed was about 100mm between tie rod connections.

You can clearly see the longer tie rods are less sensitive to rack positioning errors which is a good thing, but not a factor if you set it up right.

More importantly you see the rack is sensitive to up and down height position, but not so much so to the forward and back position. This is good, because the camber adjusters change the forward and back position of the tie rod ends. Also good because the vertical height position is easier to get in the right spot than the forward and back position.

I have attached my draft bump steer calculating spreadsheet to this post.

I have set it up so the drivers side is showing the correct rack position, and the passengers side is showing the rack 5mm too low and the effect on toe change. Thought you guys might have fun playing with it.

*File deleted - there is a new version further along this post*

[Edited on 13-7-2004 by Baja Wes]

"Wes,For tie rods I use heim's with adapters and C/molly tube, or 3/4" alloy bar, gun drilled to 5/8". Much stronger than standard and I'm not sure but you could take the material spec sheet to the governing body when you take everything else"

Nice idea but not an option with the rules the way that they are.

The aim of this exercise, besides letting Wes play with his cool computer is to design / develope and make availible a FULLY LEGAL Rack and Pinion Steering setup for VW's in particular Beach Buggies.

After talking to Wes and begining to build the design he has settles upon I am pretty confident it will work and work very well.

Onya Wes 😎

Wes, great spreadsheet you generated, after i got over being bombarded with all the numbers.

Cheers

Flintstones wrote:Wes, great spreadsheet you generated, after i got over being bombarded with all the numbers.

😀 , try writing the equations in the first place 😀

I will make it more user friendly, and I'll get Excel to draw a top, side and front view of the beam as a chart. Should be able to animate it too. 🙂

Baja Wes wrote:I will make it more user friendly, and I'll get Excel to draw a top, side and front view of the beam as a chart. Should be able to animate it too. 🙂

Cool. Very cool.

I've looked at the XL equations to try and figure out what's going on...... intense...... got to hard, I'll have to look into them a bit more when I have time.

Some one has probably come up with this already- what about getting a steering box from a LHD Beetle,remove the input shaft and welch plug the holes-mount it up on the LH side of the beam,then fit a short track rod from the RH side to the left and cut and shut the normal LH one for the centre bit.This would use the LH steering box as a normal idler arm. Could still use the damper-just relocate the fixed end mount.Should eliminate the bump steer??????

nbturbo wrote:Some one has probably come up with this already- what a
<snip>

Should eliminate the bump steer??????

When Wes first revealed that the short tie rod side had less bump steer than the long tie rod side I thought about doing this. I even started to track down gear. All you would need is a dead steering box to gut for the passenger side and a US (LHD) pitman arm which can be bought easily from the American after market. You then use the LHD pitman arm on the left idler box and you will reduce bump steer and not have a long tie rod to bend.

This got put on simmer until we had a definite answer about whether the Rack would work.

To be sure this would work we'd need to get Wes to remodel the stock setup and confirm there is minimal bump steer on the short tie rod side.

nbturbo wrote:Some one has probably come up with this already- what about getting a steering box from a LHD Beetle,remove the input shaft and welch plug the holes-mount it up on the LH side of the beam,then fit a short track rod from the RH side to the left and cut and shut the normal LH one for the centre bit.This would use the LH steering box as a normal idler arm. Could still use the damper-just relocate the fixed end mount.Should eliminate the bump steer??????

You could, but I think it would be easier and cheaper to install rack and pinion which has heaps more benefits than just the elimination of bump steer.

If you spent alot of time you could probably adjust the original set-up for minimal bump steer. The problem that I see if that it's very difficult to get the original parts in exactly the right spot in order to get minimal bump steer. Things that can stuff up the stock steering geometry and give bump steer (with idler or not);

1 - Stock steering box rotation on the beam. This is not 100% accurately located. The underside claim is kinda doweled to the beam, but then long bolts attach the steering box. So if you tighten one bolt more than the other, the steering box can essentially end up in a range of different angles. The steering box should be dowelled, not the lower clamp.

2 - stock camber adjusters. These effectively change where the tie rod connection is relate to the top ball joint. The steering box cannot compensate for this, so the stock steering box location can only be exactly for one specific camber adjuster position.

There are other factors I will explain later.

The rack will be prone to the same probs, but can be factory set in a kit form to suit the camber adjusters at a specified orientation. The rack can also easily be shimmed and moved to eliminate bump steer if the owner wants to fine tune it that much.

Once you could locate a LHD steering box and pitman arm it would be a simple fit up-just measure and weld some new locating lugs.I am not quite sure what the reference to camber adjusting has to do with this because as you said that its a given no matter what steering you use-is even relevant to any new motor car if you alter from the factory specs.Small camber alteration from stock would have minimal effect on geometry and would be at its worst on full lock where a specific toe out on turns is required.Setting up the 2 steering boxes should be simple enough with straight edges and tape measures.From memory setting the correct steering box/Pitman arm inclination is as simple as making sure the steering shaft is located centrally in the outer tube.Years ago when we used to lower our Bugs by cutting the tubes and turning the locater, B4 we knew about castor shims,we found the way to moderately fix bump steer was to adjust the steering box on the torsion tube and have the steering shaft as high up in the outer tube just enough without rubbing. Just put a bit of strain on the rubber coupling but seemed to work OK. From my limited understanding of steering geometry it would appear that to fit a rack and pinion set up you would just need the steering rod fulcrums/pivots on the rack(in the centre/straight ahead position) to end up in exactly the same postion on the car as the original RH inner tie rod end that is attached to the Pitman arm and the LH inner that would be on the Pitman arm of the conversion with a LHD box as I have described,both in the straight ahead position. Volkswagen designed the the length of the Pitman arm in relation to the steering arms to be a set distance back from a centre line thru the torsion bar tubes or a centre line thru the King Pin/ Ball Joint pivots.Hope this makes some sense.

I think its a Passat rack...

Wes, Just wanted to find out if ride height made any difference to the positioning of the rack. Say I wanted to lower the car 2-3" would that programe of yours be able to calculate if there was any change?

VWCOOL, passat's have the racks in front of the spindle, where as beetles have the steering behind. If you fitted a passat rack on a beam front end, when you turn the steering right, the car would go left.....

cheers

The problem with the 2 steering box idea is that you would have to get the design completed by the engineer and then approved. What I am saying is if your going to that much bother then why not just go to a rack and pinion design and get rid of the troublesome steering boxes that love to wear out and get flat spots in the center.

The comment on the camber adjusters is that moving them moves the best position for the inner tie rod ends forward and back. With a rack design, you can shim the rack forward and back to suit. With a steering box you can't do anything. Rotating the steering box around the beam mainly moves the inner tie rod ends up and down, which is not where the problem is.

The Excel sheet has a row (26) that calculated the length of the tie rods to have 0 toe at a given ride height. To change the ride height it's set at, simply change cell A26. set it to like -4 degrees for the upper torsion arm angle, or whatever angle you want. With a good rack design with no bump steer it won't matter where the normal ride height of the car is. But you can see with a set-up which is wrong it simply moves the bump steer curve around, and you still have the same amount of bump steer.

The Excel sheet can be used to look at the two steering box idea, or the stock setup, or a rack set-up. Simply change the coordinates of where the inner tie rod ends are.

From what I have measured so far, the stock set-up isn't right anyway, even for the short tie rod. I need to do some more accurate measurements though.

Here's a 2nd draft of the Excel spreadsheet for calculating the bump steer.

You only really need to change the rack mounting position and see the effect. I also added a side on and top view of the front end, drawn as Excel charts. It does the job.

There is a little "+" and "-" button for rotating the beam and watching it move. I am going to put an animate button on there but my computer keeps crashing when I try to write the macro (I'm on my old crappy computer at the moment). Anyway, have fun playing. 🙂

PS - it's a zip file this time to keep it under 50kB.

*File deleted - there is a new version further along this post*

[Edited on 13-7-2004 by Baja Wes]

Measuring balljoints

Guessing ball middle to ball middle because the balls aren't spherical.

best guess 167mm

Measuring balljoints

Ball bottom to ball top. Balls have a flat spot on the top which makes this difficult.

best guess 167mm

MikeM wrote:Measuring balljoints

best guess 167mm

Thanks for measuring that for me. You can see in the excel sheet above your post I had it as 167mm too. So it's good that we agree, a nice check measurement 🙂

I'm actually suprised since I measured a fully assembled beam laying it flat on the shed floor and then using set squares and rulers and guessing where the center of the ball looked like it was 😀

here's another revision to the Excel sheet.

The last one had a small error when drawing the drivers wide wheel, it made it rotate the opposite way to the toe in, a + and a - sign in the wrong place. The bump steer calculation was still ok, but when it drew it as a stick diagram it wasn't quite right. fixed now.

I also put an animate button on the diagram page. I can't seem to make Excel animate it any faster, so it's a little slow.

[Edited on 19-7-2004 by Baja Wes]

I received an email that has some questions that other people may find relevant....

Hi Wes,

I've been playing with your rack and pinion spreadsheet but have a few questions.
1) I updated the info with my specifics - 205/50-16 tire size, plus inner tie-rod joint width of the Flaming river R&P unit (603.7mm). Niether of these is very far off of your original dimensions.

It looks like placement of the rack - both up and down and forward and back is extremely sensitive! Even slight movement really skews the bump-steer characteristics. Your original settings for rack position look to be about the best overall - I'm just wondering how one would implement them in a real-world installation. Seems like once your main attachment points are fabricated and installed - both front-back and up-down shimming/adjustments would be necessary to really get it dialed in, in small increments of movement. Especially when you're talking about dimensions of less than 0.1mm making a fairly large change!

On the lower section it states: "Table below calculates tie rod lengths, enter angle car normally sits at"
Where is this angle entered? Is this the overall chassis angle of attack or trailing arm angle?
Referring to trailing arm angle, I know you're working this up for an off-road application but I'm dealing with on-road, with most likely much less suspension travel - probably only around 130mm travel total. How can I plug this value into the spreadsheet, probably with a minimal top torsion arm angle (maybe about 4 degrees down?) as the normal static attitude of the upper arm? How does this affect the angle of the lower arm (or is this automatically compensating?)

Very neat work on the spreadsheet though - fun to play with!

Cheers,
Jeff

Hi,

A lot of this stuff has been covered on the www.aussieveedubbers.com forum. I have attached the latest version of the spreadsheet so you can play with it.

Yes it is very sensitive to position of the rack. In order to address this you need to be able to shim it up and down. So yes you would trial fit it, then measure the bump steer. Using the excel sheet and comparing to the bump steer pattern you measured you should be able to accurately shim the rack to the correct position (by figuring out how far out, and in what direction it's out).

A center mount rack would be less prone to the problem. You would get half the error because your tie-rods would be twice as long (roughly speaking)

The funny thing is the stock steering box set-up suffers the same sensitivity to set-up accuracy. The stock short tierod will be very similar to a rack design. From my measurements so far, the stock tie rod end centers on the steering box appear to be located at;
drivers - 255, 36, 119
passengers - 215, 41, 104

You can plug those figures into the rack location in the excel sheet and see what the stock set-up is like. The problem the stock set-up has is that it is not adjustable or shimmable. Whereever it ends up is where is stays.

The angle the steering is set-up at is referring to the angle of the top trailing arm. -4degrees would be slightly up, +4 would be slightly down (lowering relatively speaking). You can see this just moves the bump steer curve left or right essentially.

If you don't want to use the full suspension travel then just ignore the upper and lower measurements. The big calculation table that is now grey in colour shows the upper trailing arm angle, and for each angle you can read across and read the "y" value which is essentially the suspension height in mm above or below a top arm angle or "0 degrees" (horizontal). And yes it calculates what the lower arm angle is for any upper arm angle.

Wes

This stuff is way over my head, but I'm curious to know how this all panned out.

here here...

i am intersted...does that mean the 75 pan i got sitting round..nicley restored will make a nice buggy????

It is moving just fine .... :party

just thought I'd reattach the rack spreadsheet for compulsive tinkerers. You will probably need Excel 2000 or later.

[ Edited on 5-7-2006 by Baja Wes ]

it is still going ... finding the time to play with stuff is the hardest thing right now .... to many damn subaru engines to play with ... hehehe

Anyone end up putting rack and pinion on something?

ANd if so, what rack did you use and do you have a pic?

I heard something about a charade rack on a buggy in VIC some time ago.

I ended up fitting a CB Performance steering rack to my race car
Tiny rack at a tiny price.

Simple to fit in a Vee.

Altho the bump steer characteristics are pretty ordinary when mounted directly inline with the stub axle pickup points, with the amount of travel I am using, and the positioning of the rack in relation to the balljoint heights, the amount of bump is pretty much academic.

L8tr
E

posting the spreadsheet again cos the last one has corrupted for some strange reason

[ Edited on 4-7-2006 by Baja Wes ]

An absolutely terrific job Wes - and the timing couldn't have been more perfect as I'm in the process of replacing the cactus rack on the buggy with a new one which is centre load instead of end load and the front beams have been widened as well, so it's all highly relevent. However, I do have a couple of quick (and probably dumb) questions Wes:

1) "Spacing of the upper and lower torsion tubes" on the general measurements tab, I'm assuming that's the distance between the theoretical centre line of each tube ie where the arms pivot, as opposed to the actual gap between the tubes ?

2) If applying this to a K&L front end you'd presumably substitute the relative ball-joint "positions" for link pin positions - however, is there anything else in the depths of your calculations that need to be changed to handle K&L ?

Thanks ... Kimbo

yes, spacing of the tubes is to the tube centerlines. Off the top of my head I think it's 120mm K&L and 150 BJ?

Don't worry about getting the beam spacing right, it doesn't make a difference to the calculation.

I haven't measure the K&L front end, but I assume all the work points will be in the same place, as the K&L and BJ fronts use the same steering box, therefore must be the same geometry.

The only thing that will catch you out is using longer front arms.

I was looking for a tool like this. I'm building a Kelmark from scratch using a Ford Contour 2.5 V6 and 5 speed in a mid-engine position. The front end is a modified Karmann Ghia disc BJ beam. I cut it, widened it by 4 inches, and welded in 4 adjusters.... I also shortened the torsion bars by 15 percent to make the suspension stiffer for the lighter body, and sports car handling. I will probably use a power steering rack (quicker ratio than manual racks) and just loop the pressure side port to the return port. You've done a great job on modeling the beam, while allowing adjustment parameters where I need them. I'll be able to fab a mount with the correct scale of shim available for nearly no bump. Thanks very much.

Gar

I used the spreadsheet formula to locate the rack for minimum bump steer, but find that in doing so, I have an Ackerman problem. This is a result of the sharp angle that the tie rod makes between the end of the rack, and the tie rod end. If you look at the graphic you'll see this angle in the overhead view. The original Ackerman uses both the long pitman arm length, and the dual inner tie rod end slightly offset (dog bone) in combination with the angle of the steering arms on the spindles to properly control the inner wheel turning more sharply than the outer wheel. Following the design information for rack placement, you'll create anti-ackerman. Your wheels will toe in, rather than toe out as they should in a corner. Using a rack and pinion in place of the original design will mean accepting a compromise, either bump steer or Ackerman. I will be moving my rack further away from the torsion tube and will accept more bump steer. I'll post and let you know how the bump compares to the original with the Ackerman where it needs to be for low steed steering.

I never got around to calculating the Ackerman for the VW. It's more complicated than it first looks.

Basically we decided (being interested in offroaders) that the bump steer was more important than the ackerman. You feel the bump steer when trying to travel straight. This is a problem when trying to go fast on a bumpy road.

If the ackerman is out then it just changes the oversteer / understeer tendancies a little. This has a much more managable impact. And when you corner all the weight is on the outside turning wheel so what the inner wheel does doesn't matter that much.

Drive a manx buggy and you will see having completely stuffed up ackerman (because the wheelbase got shortened 14.5") doesn't have that bad of an impact. It is a lot less noticeable then when the bump steer is bad.

The rack set-up prototype that we came up with has centre mounted tie rod ends on the rack. This prevents the really tight angle you get with the end mounted tie rods (on the rack).

The VW ackerman appears to converge just in front of the rear axle. Either shortening the wheelbase, or widening the front would appear to compensate, BUT, it's not really off in the first case. The arms on the spindles are positioned to compensate for the fact that the VW doesn't use a drag link connecting them. Instead, the angle that the tie rods leave the pitman, and the subtle offset on the pitman for the two sides makes the ackerman correct. If you use a drag link you will have excess ackerman. The steering arms on the spindles would need to be bent, and I don't want to go that route. Using the longer tie rods in a center loaded rack, and including some tie rod angle (close, but not exactly like the original pitman set-up) should be the closest compromise. I grew up on shortened buggies and know that feeling of flying just above the ground on the edge of control.
I was considering a drag link, but for now I'm fabricating a second rack location. I can't go back to pitman because my beam mounts to the frame in such a way that the pitman is limited in movement before hitting the frame. Before I buy anything, I'll toy with some 'tween rack locations. If I buy, it will be a center loaded rack. The aftermarket ones all seem to have the pinion dead in the middle, and over complicate the steering wheel linkage. I'm a spreadsheet guy too, and I'm busy with the work already done, modifying and adding little details like body height to the graph. Since my project is a sports car, my suspension travel is small. I widened my beam, and while doing so, shortened the tosion bars. This reduces the bump steer where I hope I can move the rack rearward without getting too much bump. Bad thing is.... the bump will ramp up steeply at the worst time... in a nose dive braking situation, or severe body roll corner. Thanks for the great foundation to help describe the front end, I'll let you know how I end up.
Gar

Wes,
this is a fantastic thread and the work you have done is very comprehensive to say the least. :thumb

But lets get to the nitty gritty!!!

It's been over a year since the last post! Where have you ended up on this mission --- "to get R&P legal in Qld" ???

Cheers
Matt :thumb:thumb:thumb:thumb

🙂

We got to the stage of fabricating a jig to hold the rack in the correct place for installation, and had a rack all ready to go, but none of the interested parties could be bothered during the final fabrication and going through with it 🙁

I don't see a need to pull my car to bits to install it, and the other people interested ended up selling their buggy projects. The parts are still around and may end up in something. The approval engineer didn't have any issues with it as we were using a combination of standard steering parts, and we could prove the bumpsteer would be fine.

Mate that sounds very interesting.. I am starting a baja project as we speak!!!
Rack sounds real good. How do we get started?

Matt👍👍🙂

My Iguana Buggy has Rack and pinion going into it, it is in there now for mock up.

brad ive sent you a few (lots) of email's could you send me an email
exxhippy@hotmail.com

I'll check it out Brad, next time I'm in, assuming COR.

Matt.

newoldmanx wrote:brad ive sent you a few (lots) of email's could you send me an email
exxhippy@hotmail.com

Done

matberry wrote:I'll check it out Brad, next time I'm in, assuming COR.

Matt.

Nope it is in our other shed

hi there guys ..... now i have a question that i thought kinda in a way is ok for this thread

a lil while back i was looking over to sandrail type looking buggies ( race i guess as they had numbers and stickers on them .. lol ) and what i found was a ver ununusual steering setup ,, couldnt find an owner to ask about it either .. soo here is what i found


instead of runnign rack and pinion or a standard steerin box set up both of these buggies used twin vw steering boxes,,, however only one of the steering boxes was linked to the steering colum..

it looked somthing like this ( sorry about the bad paint but you get the idea.. i hope )

now the only thoughts i had on this was to ... A ) instead of having one long arm there is now 2 short arms ,, and B) maybe add a lil bit more resistance in the drive line ..

does anybody know anythign about this set up and if it actually has a purpose ?? and if so what ??

cheers guys

hmm my paint picture didnt show up but basically there is to steering boxes side by side ( abotu 800 - 1000 apart) connected by a draglink style of bar connected to 2 rose joints at eother end that link to the tie rods .... and ony one box is connected to the steering colum

not sure if that made sense :P

i find it picture for you rack in buggy gold coast

im think it is named volksmod?

The twin steering box has already been discussed on this thread. 1970's technology.

matberry wrote:The twin steering box has already been discussed on this thread. 1970's technology.

...so, about 40 years smarter than the rest of the design! :P

helmut wrote:im think it is named volksmod?

Yes, that is Kurt and Gunter, we know those guys. When they first installed that R&P in their buggy they put it in the wrong spot and it had huge bump steer problems. I told them about all the info in this thread to help correct the issue.

Baja Wes wrote:

helmut wrote:im think it is named volksmod?

Yes, that is Kurt and Gunter, we know those guys. When they first installed that R&P in their buggy they put it in the wrong spot and it had huge bump steer problems. I told them about all the info in this thread to help correct the issue.

It has now been moved an is much better and in the correct position.

Baja Wes wrote:

helmut wrote:im think it is named volksmod?

Yes, that is Kurt and Gunter, we know those guys. When they first installed that R&P in their buggy they put it in the wrong spot and it had huge bump steer problems. I told them about all the info in this thread to help correct the issue.

is volksmod doing instalation for customer. buggy is best i did seen in australia. do you know the swinging open hood i never see on manx buggy

That is their buggy, but they do also build them for customers. I think the bonnet is a custom mod.

why it is difficult for the rack steering in the vw
:duhdid you see it
http://www2.cip1.com/PhotoGallery.asp?ProductCode=C26%2D425%2D170&PhotoNumber=2#largerphoto
🙅 and
http://www2.cip1.com/ProductDetails.asp?ProductCode=C26%2D425%2D165
😎
also many company selling beam with rack mount
the rack and pinion steering into vw it is very easy


[ Edited on 12-10-2007 by helmut ]

mods are easy. Doing them practically and legally is where it gets tricky.

MikeM wrote:mods are easy. Doing them practically and legally is where it gets tricky.

:duh this is the page 8 of "how to", "akerman", "where to put it rack is most important" etc
you are make it not easy if want🙅
here is it you buy for $260us is about $290au bolt out bolt in
then what??
is not a-arm

The Key to what MikeM said though is Legal. Bolt out Bolt in does not mean it is legal for the roads in Aus. I guess even with those new beams you gotta go through all the crap. But I have no experience with this sorta thing.

But I see your point there are stacks of products where perhaps allot of the hard work is already done in the US that can be suitable. Oh yeah and some real nice gear 🙄

helmut wrote:the rack and pinion steering into vw it is very easy

So I guess you have already got a blue plated and registered car on Australian roads with a rack and pinion in it and no bump steer?

The rack and pinion setups they use in the offroad race cars in the US are not legal for street use in AUS. If it was that easy we wouldn't have even started this thread.

MikeM wrote:

helmut wrote:the rack and pinion steering into vw it is very easy

So I guess you have already got a blue plated and registered car on Australian roads with a rack and pinion in it and no bump steer?

The rack and pinion setups they use in the offroad race cars in the US are not legal for street use in AUS. If it was that easy we wouldn't have even started this thread.

you guess is wrong im not having car in Australia

also did you see it this car:thumb
is registered in Australia on the road yes?

:duh is same position for rack:duh

did you see it you have it also off the road race car in aust for very long with rack

[ Edited on 13-10-2007 by helmut ]

[ Edited on 13-10-2007 by helmut ]

MikeM wrote:

helmut wrote:the rack and pinion steering into vw it is very easy

The rack and pinion setups they use in the offroad race cars in the US are not legal for street use in AUS.

for off the road racing in Australia it is here http://www.offroadracing.com.au/ many racers have been using the rack for very long in Australia too not just the U.S.A

1. A photograph of a car with something fitted to it does not mean it's legal.
2. The R&P boxes fitted to "race cars" are not legal for use on registered vehicles in Australia. They are easy to fit etc...but NOT legal. An "Offroad race car" is NOT a registered vehicle. Isn't this discussion dead in the water yet or are people just going to go around in circles repeating themselves??👎

MickH wrote:1. A photograph of a car with something fitted to it does not mean it's legal.
2. The R&P boxes fitted to "race cars" are not legal for use on registered vehicles in Australia. They are easy to fit etc...but NOT legal. An "Offroad race car" is NOT a registered vehicle. Isn't this discussion dead in the water yet or are people just going to go around in circlesrepeating themselves??👎

1. " A photograph of a car with something fitted to it does not mean it's legal."

is also not mean is not legal too !!!!! car has it number plate and sticker tags !! are you say this car is not legal???

2. i am think it is more position akerman angle bump steer...was being talked in this section talk

3. i am not knowing you have car registerd for offroad in Australia you laws are very bad is this mean motor limit for registered offroad vw is same as on the road

Buggy Brad wrote:My Iguana Buggy has Rack and pinion going into it, it is in there now for mock up.

is car register for on road or off road

if is on road did you know what r&p it is legal to use it in Australia

helmut wrote:

Buggy Brad wrote:My Iguana Buggy has Rack and pinion going into it, it is in there now for mock up.

is car register for on road or off road

if is on road did you know what r&p it is legal to use it in Australia

Whatever unit is fitted would require engineer approval to enable it to be legally registered,which Brad's will be . A "registered"car can be used both on and off road so when you see Brads Iguana it is registered as a road vehicle but is very capable as an "offroad" car...
"Offroad race cars" are a different kettle of fish...you also can't drive them down the street....legally🤖 as they are not registered......gets confusing doesn't it....😂😘

helmut wrote:

MickH wrote:1. A photograph of a car with something fitted to it does not mean it's legal.

1. " A photograph of a car with something fitted to it does not mean it's legal."

is also not mean is not legal too !!!!! car has it number plate and sticker tags !! are you say this car is not legal???

NO...I'm in NO WAY suggesting that this car is not legal...but you should not assume that as 1 person has done something that it is OK for everyone to just go and do it to their cars. NOTHING like this is a simple bolt on,especially with this applcation of using R&P steering,as even if you are using "bolt on" stuff from the US of A there is a very high chance that it would not pass engineering for Australian standards. All this stuff requires the approval of an engineer who specializes in motor vehicle modifactions and who is authorzed to permit these types of modifications...to REGISTERED vehicles..❗

is it owner/builder on this forum im like this car

MickH, if we ignore it, it might go away.

Baja Wes wrote:So I modelled the center rack, at the rear (same as first pic).

I played with the Excel sheet to get it in the back spot, but still near the firewall like the pic shows. The Excel sheet was giving around 29mm of toe change per wheel.

Then once modelled the model gave 5 degree change per wheel, which ends up equalling about 29mm toe change per wheel. So that's a nice check of both methods, it's good they agree.

my point is being is good but not need is very waste of time for 7 pages of angle and geometry 😊

you liked it to talk like you know steering geometry and im know it baja wes is understand but not everyone else here im offer solutions for you ppl easy solution but im also know you did not try it the wheel is already invent from an engineer im know that if is safe maybe xray the weld check it bump steer ackermans rack integrity must pass if brad is doing you can do too in usa we have it people talk and people do it is sad in Aust it look worse



did you try it bolt on front end from states at engineer in Australia what did it say???

MikeM wrote:

helmut wrote:the rack and pinion steering into vw it is very easy

So I guess you have already got a blue plated and registered car on Australian roads with a rack and pinion in it and no bump steer?

The rack and pinion setups they use in the offroad race cars in the US are not legal for street use in AUS. If it was that easy we wouldn't have even started this thread.

"MickH, if we ignore it, it might go away."

problem problem problem problem problem problem problem problem

🤓

=give up tell every people is hopeless this is not help anybody
❗❗

what is YOUR SOLUTION??

Helmut, the problem is the LAW in Oz does NOT allow these aftermarket parts to be fitted to your car!!
So the offroad race rack is not legal
Need to find one that is strong, fits and RHD.
The a arm link posted a week or so ago used Golf rack.

matberry wrote:Helmut, the problem is the LAW in Oz does NOT allow these aftermarket parts to be fitted to your car!!
So the offroad race rack is not legal
Need to find one that is strong, fits and RHD.
The a arm link posted a week or so ago used Golf rack.

i am hear you but...

did YOU try it

what is reason they tell YOU for not approve

i an know you can take it to 10 engineer and get 7 answeres🤓

ok more solution
use it stock torsion house copy position of rack from race house fit approved centermount rack😵‍💫

i know this thread is pretty old , but reading it last night i remembered seeing this on a car in melb (at day of?) a few years ago now , maybe 2004 ?






i realise its been considered "1970's technology. "
thought i would post it anyway 🙂

mm interesting thread ...... if only everyone could learn to read.

In short

The WRight Racks, Trik Racks, CORC Racks, etc etc ARE NOT NOW AND NEVER WILL BE ROAD LEGAL IN AUSTRALIA (without considerable $$$ being spent)... is that clear enough for you all to understand ??

Have I tried it ?? YES I HAVE,

The rack in my buggy is ADR Compliant, ie it is already approved as it is from an existing production vehicle. The fitment is design is approved (with considerable effort from Wes) and once complete the installation approval can be given.

Rack and pinion is an engineered solution not a bolt in yank solution with bump steer .. yes that is correct those centre mount race racks have bumps steer and allways will have. We make them here in Australia and I know they have it. BUT in a offroad race car it is less of an issue and the front ends are usually wider so it is less than a stock width beam. Most also bank on having 9 degrees added into the frame head.

In the USA you can register a sand rail for crying out loud ........

avwboy wrote:i know this thread is pretty old , but reading it last night i remembered seeing this on a car in melb (at day of?) a few years ago now , maybe 2004 ?

[IMG]
i realise its been considered "1970's technology. "
thought i would post it anyway 🙂

Nice pics, Boy, it is something that will no doubt 'even up' the toe change from side to side, with a possible/probable benfit to handling, especially under hard braking...

I gutted a steering box a decade ago to achieve a similar result, but never got around to installing it in my car... I am re-inspired (is that a word?!) to do it now

The advantage of the idler arm set-up in those pics is you eliminate the weak long tie rod (which you can get around by just making it stiffer anyway), and you don't need to clearance the tunnel for the long tie rod if you have a lot of down travel. So although interesting, I'm not sure of the point of it. Old holden has that set-up, but that was to eliminate the need for a big tie rod swing area through the lower suspension / engine area.

wow 🤪 its been awhile since ive ventured over to avd but seeing as im buying the bolt on a-arm convertion for one of my buggies i thought id have a squiz over here not much has changed eh 🙁 but ......... i think my buggy and possibly kurts might have been some of the only manx builds that got a rack n pinion steering way back in 82 when it was built so i have no need for any blue tags are there any others that are around???

Ok well my Iguana now has Rack and Pinion steering in it which is ADR Compliant and has passed engineering inspection # 1 ..

Big thanks must goto Wes for designing it, Dave (Custom Vee Dub) for building it and me for buying lunch and sweeping up afterwards.

After a few hours of dicking around we got it to 1.5mm bump steer over 195mm of travel. Although it ain't the zero I was after it is a very fidly thing ...

Anyway it is in, Iguana Steers well and I was very happy putting it on the trailer for the first time with steering.

The rack is 4/1/2 Turns lock to lock ..

Yippy ...

This shows the jigs I had laser cut. Wes designed them to allow Dave to rotate the Rack around the correct axis to maintain minimal bump steer but still position it to suit the application

I will be doing a tech article for thr Next Manx Mania next year on it and will also do a write up on my Buggy Build thread on the Manx Club Forum (www.manxclub.org)

ah, the proof is in the pudding 🙂

Baja Wes wrote:ah, the proof is in the pudding 🙂

Yes it is and just to show it all actually exists and stuff .. here is a pic with the heavy duty custom tie rods and rack all fited up just before I put it back on the trailer.

Whats the pipes coming out of the tunnel with the rubber hoses on them ??

For the wet stuff I'd reckon.

LIFE IN THE LOW LANE wrote:Whats the pipes coming out of the tunnel with the rubber hoses on them ??

Man they are my oil cooler lines, you can never have enough oil in those air cooled engines.

so another vw problem solved, when is the bolt on version ready for sale?😁

sign me up for one!

anyone done racket peanut steering on type 3?

Bit of a long shot, any of the original posters still on here? I'm trying to fit a rack in my buggy, I came up with similar mounting position to Wes' - but I now have serious anti-ackerman and I'm not sure why, or what I can do about it. My rack is 400mm long, mounted at 91mm back 29mm high, so bump steer is 'not too bad' but will be fine when moved to match wes' but is there anything at all I can do about ackerman as this will be a daily driver too...