| [ Total Views: 167963 | Total Replies: 173 | Thread Id: 23861 ] |
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 Brad
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| posted on July 7th, 2004 at 10:43 PM |
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"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 
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Flintstones
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| posted on July 8th, 2004 at 09:47 PM |
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Wes, great spreadsheet you generated, after i got over being bombarded with all the numbers.
Cheers
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Baja Wes
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| posted on July 9th, 2004 at 08:16 AM |
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| Quote: | Originally
posted by Flintstones
Wes, great spreadsheet you generated, after i got over being bombarded with all the numbers.
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 , 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.
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MikeM
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| posted on July 9th, 2004 at 11:03 AM |
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| Quote: | Originally
posted by Baja Wes
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.
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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.
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nbturbo
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| posted on July 9th, 2004 at 03:52 PM |
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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??????
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MikeM
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| posted on July 9th, 2004 at 04:05 PM |
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| Quote: | Originally
posted by nbturbo
Some one has probably come up with this already- what a
<snip>
Should eliminate the bump steer??????
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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.
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Baja Wes
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| posted on July 9th, 2004 at 04:59 PM |
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| Quote: | Originally
posted by nbturbo
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??????
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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.
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nbturbo
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| posted on July 10th, 2004 at 02:01 PM |
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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.
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VWCOOL
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| posted on July 10th, 2004 at 05:31 PM |
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I think its a Passat rack...
Pay your debts, CxxT
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Flintstones
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| posted on July 10th, 2004 at 11:25 PM |
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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
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Baja Wes
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| posted on July 11th, 2004 at 11:01 AM |
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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.
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Baja Wes
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| posted on July 11th, 2004 at 08:16 PM |
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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]
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MikeM
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| posted on July 12th, 2004 at 12:30 AM |
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Measuring balljoints
Guessing ball middle to ball middle because the balls aren't spherical.
best guess 167mm
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MikeM
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| posted on July 12th, 2004 at 12:32 AM |
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Measuring balljoints
Ball bottom to ball top. Balls have a flat spot on the top which makes this difficult.
best guess 167mm
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Baja Wes
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| posted on July 12th, 2004 at 08:18 AM |
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| Quote: | Originally
posted by MikeM
Measuring balljoints
best guess 167mm
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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
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Baja Wes
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| posted on July 13th, 2004 at 12:53 PM |
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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]
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Baja Wes
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| posted on July 15th, 2004 at 01:37 PM |
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I received an email that has some questions that other people may find relevant....
| Quote: | 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
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Hi,
A lot of this stuff has been covered on the http://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
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Jenny
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| posted on October 21st, 2004 at 12:25 PM |
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This stuff is way over my head, but I'm curious to know how this all panned out.
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DoNkEy
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| posted on October 21st, 2004 at 03:30 PM |
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here here...
i am intersted...does that mean the 75 pan i got sitting round..nicley restored will make a nice buggy????
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Brad
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| posted on October 21st, 2004 at 07:01 PM |
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It is moving just fine .... :party
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Baja Wes
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| posted on March 4th, 2005 at 10:13 PM |
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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 ]
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Brad
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| posted on March 5th, 2005 at 10:49 AM |
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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
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pete wood
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| posted on May 26th, 2005 at 03:00 PM |
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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.
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tassupervee
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| posted on May 26th, 2005 at 08:49 PM |
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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
Im not a complete idiot, quite a few parts are missing....
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Baja Wes
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| posted on July 4th, 2006 at 08:50 PM |
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posting the spreadsheet again cos the last one has corrupted for some strange reason
[ Edited on 4-7-2006 by Baja Wes ]
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Kimbo
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| posted on July 25th, 2006 at 03:10 PM |
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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
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Baja Wes
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| posted on July 27th, 2006 at 09:32 AM |
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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.
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FakeDino
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| posted on July 29th, 2006 at 10:44 AM |
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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 |
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FakeDino
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| posted on August 15th, 2006 at 12:41 AM |
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Ackerman problem
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. |
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Baja Wes
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| posted on August 15th, 2006 at 08:55 AM |
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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).
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