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Author: Subject:  Coilover conversion and spring rate choice
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posted on December 4th, 2007 at 04:17 PM
Coilover conversion and spring rate choice


Hi all,

Some of you may have noticed the chassis I am posting the build for in the drag forum. I want the chassis to perform around corners as well as in a straight line.

For starters though I just want a set of springs that will be suitable for general street use, and the absolutely crap roads of Cairns.

So, time has come to choose my spring rates for my coil-over conversion. I was thinking 130lb front and 180 / inch rears.

Does anyone have any experience in running coil-overs at all 4 corners?

The coilovers I will be using are modified honda crx with adjustable dampeners. I also have a set of 14mm and 16mm whiteline swaybars for the project.

Feel free too jump in with suggestions :D

Cheers,
Ian
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posted on December 4th, 2007 at 05:12 PM



It would probabley help those in the know if you know what the front and rear weights are , + and in the front also trying to take into account fuel at different amounts .
Mabey talk to Big Rudi as isn't his circuit car a coil front ended super bug or mabey even Richard @ V Forse as he would have had to do similar calcs for "Dak to The Future" many moons ago.




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posted on December 4th, 2007 at 05:16 PM



Yeah thats a tough question to answer as so much of the car is un-finished at the moment. I hope the car will weigh in under 850kg total with simular to factory weight bias.

The 930 box plus an alloy engine block will add more weight, as will the extra re-enforcing etc.
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posted on December 4th, 2007 at 05:52 PM



hi ian 180lbs on front is a good place to start for the road ran this set up for a few meetings still plush ride and good handling am now running 300 oneach corner ride is still good and turn in is awsome if you need any more info give us a call 0418442953 rudi
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posted on December 5th, 2007 at 07:44 AM



Most drag cars run 500lbs or more on the rears.
(mine were 550 because a line passing thu the shock contacted the ground at the wheel centre line contact,
Rodneys were 700 to 750 because of where his lower shock mount was, bottom mount further in-board).

You do not want the suspension hitting the stops.

This will vary depending on mounting locations.
The rate I have quoted is a "wheel rate".
Yours may have to be different depending on your rear geometry for mounts.
I am guessing higher due to the effect of the leverage from the wider track
in relation to where the shocky/coil will be.




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posted on December 5th, 2007 at 09:42 AM



when I started my project I was thinking similar thoughts but I cam to the conclusion that I may as well just build a chassis from scratch based on a westfield or similar. In relation to using rear coil overs I have also been informed that the shock tower are not capable of handling the loads so you will need to build a Reub like frame for the rear, however I guess you are planning on this already. There used to be a place in Canada that sold frames to suite beetles that had front and rear A-arm suspension, I vaguely remember seeing an add in an American mag, something like this would break you free of the limitations of the chassis + you could sell the plans to other punters :) I know I'd be interested.



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posted on December 5th, 2007 at 10:33 AM



Hi Ian,

I can see you're capable of executing a complex project and I'm not meaning to be negative but, reconfiguring the suspension adds a lot of hurdles that can hold up a project. Think about Richard Holzls Dak to the Future that's never hit the track and JVL's oval that used to bump-steer in a straight line and then disappeared.

What's wrong with using bigger torsion bars, good shocks and the right size tyres R-spec tyres that will get to 60 degrees plus quickly?

Is it just that you've cut into the torsion spring anchor points to fit the big gearbox

Regards CT




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posted on December 5th, 2007 at 10:52 AM



Quote:
Originally posted by fullnoise
Hi Ian,

I can see you're capable of executing a complex project and I'm not meaning to be negative but, reconfiguring the suspension adds a lot of hurdles that can hold up a project. Think about Richard Holzls Dak to the Future that's never hit the track and JVL's oval that used to bump-steer in a straight line and then disappeared.

What's wrong with using bigger torsion bars, good shocks and the right size tyres R-spec tyres that will get to 60 degrees plus quickly?

Is it just that you've cut into the torsion spring anchor points to fit the big gearbox

Regards CT
.....Agree with that CT!many...$$$$
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posted on December 5th, 2007 at 12:35 PM



Yes granted it is going to be complicated, but I am confident that I can get the 944 A-arm/Mcpherson strut system to work better than the king and link system that was on the previous chassis. Frankly that wont be saying much.

Running rear torsions is still possible I think, I just need to weld in a spline section to each 1/2 of the tube and run swing axel torsion bars. The standard bump stops need to be removed and re-located as where the chassis ride hight will be, is very close to actually sitting on the bump stops. Switching to rear coil-overs will provide better axel-shock clearance as I can re-locate the top shock mount. I can do away with the bump stop all together as the coil-over has a bump stop on the shaft. The re-enforcing of the rear end can be done to accomodate the top mount easily too.

I promise you that I arent just going to jump in with both feet and weld in some crazy suspension and hope for the best. I am doing a lot of research into this project, designing the suspension with CAD, purchased suspension design software to make calculating roll centers, and camber changes through the full range of suspension movement etc. I also have the ear of a suspension guru thats working with a v8 supercar team. A 5 minute conversation with this guy has me doing research for a week so I can understand what he's just said. I am getting there slowly though.
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posted on December 5th, 2007 at 01:15 PM



Can we expect a hole in the rear window through which you can do a roll-centre adjustment?

What does your suspension guy think of the wide rear track? If I remove my 6 inch rims and bolt 7 inch wide rims with an inch extra negative offset to the rear of my car it will snap oversteer mid corner.

With the 6 inch rims the car handles beautifully and inspires confidence without a hint of mid corner oversteer.

I would not believe a change in track can make so much difference if I didn't experience it myself.

CT




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posted on December 5th, 2007 at 01:21 PM



Are you running 7's all round or just 7's on the rear with 6's on the front when you have the oversteer problem?

Roll center adjustment?

From the materials i've been researching (mostly mcpherson strut related but some double A arm related too) roll center is the point in space that the suspension moves in an arc around.

It can be calculated in cad by drawing intersecting lines from the spindle center through the pivot points. I am probably not explaining this too well.. but anway, it directly affects camber through the range of suspension movement, dynamic camber.

Roll center isnt adjustable in the normal sense of things unless you can varry the length of the top A-Arm in double A-Arm suspension to change the rate of camber gain.

Rear camber adjustment will be done using the standard 944 adjusters. I contemplated installing an adjuster at the pivot box as well. This is commonly done on some of the 911's that are update to use later model trailing arms with a wider rear offset. See the pic.

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posted on December 5th, 2007 at 01:54 PM



I found a pic to better explain roll center.

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posted on December 5th, 2007 at 02:38 PM



Hi

A friend is building a bug at the moment with Lexus struts using 944 alloy arms, he will integrate the top shock mounting into the roll cage, I imagine that's what your doing .

CT. Beetles were set-up from the factory with the front track being wider than the back, maybe the 7s on the rear of your car upset this.

Steve
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posted on December 5th, 2007 at 03:13 PM



Hi

I forgot to mention this, I have alloy 944 arms on my new 1303, they gave me 85 mm wider distance at the wheel bolt face over a stock L bug with Type 3 drums. 85 mm sounds like a lot, but when you look at the ET on late Porsche wheels they can accommodate this wider distance at the wheel bolt face without having a huge track increase.

Steve
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posted on December 5th, 2007 at 03:32 PM



Hi Steve,

I wouldnt mind having a look at some pics of your alloy A-arm setup.
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posted on December 5th, 2007 at 03:45 PM



Hi

You mean the 944 alloy arms. I can't believe it, this is the only photo that I have. You can see how far the brake rotors poke out from the body, but Porsche wheels with correct offset will bring them back under the body

Steve

http://www.clubvw.org.au/images/P9070368.jpg
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posted on December 5th, 2007 at 03:51 PM



ah... I thought you meant you had done a front a-arm conversion.. I miss-read...
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posted on December 5th, 2007 at 07:51 PM



Ian, do you have any more pictures of the yellow car above? looks wicked ;)



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posted on December 5th, 2007 at 08:42 PM



Yeah, i pinched the pictures of the 911 from this website. I came accross the rear camber adjustments when looking for a nice aftermarket shifter to suit the 930 gearbox. This car has a fabcar shifter.

http://www.autometricsmotorsports.com/products/911/index.htm 

I am helping out with a 911 build at the moment too. Its being built for hill climbs and sprints. Check out the address below. Next on the list for that car is 996 brakes, bilstein suspension, 18x8 and 18x10 RUF wheels, and a strengthened 915 box with a 3lt turbo 911 engine. The owner is posting the entire build. The car has a bolt in 1/2 cage but will have a full SC style interior when done, with no back seats.

Ive done all the welding, widebody guards and replaced the battery tray and suspension support area at the front which had rusted through, and will be wiring the car as well. Bril did all the panel work.

Not bad for a couple of IT geeks hey!

http://www.allcorp.net.au/911/ 
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posted on December 5th, 2007 at 10:10 PM



is your mate building a yellow bird tribute (RUf car that they hooned round the Nurburgring, amazing video :) ) Looks like it will look the business :tu:



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posted on December 5th, 2007 at 10:16 PM



I dont think its a tribute no though he is a fan or the ring. I think its being built because he wants something diferent thats not a Jap car. Most of the car scene up here is either V8 or Jap. His previous car was a 500rwhp supra. That was a dam fast car, but the porsche will handle where the supra didnt.
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posted on December 5th, 2007 at 11:46 PM



http://video.google.com/videoplay?docid=7007840369175411712 for those of you not familiar with the yellowbird :)



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posted on December 6th, 2007 at 07:21 AM



Hi Ian

When do you sleep, building your car and helping out the Porsche guy, wow. Have you seen this Double A arm post on German Look? http://www.germanlook.com/Forums/showthread.php?t=2070 

Steve
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posted on December 6th, 2007 at 09:12 AM



Quote:
Originally posted by 555bug
http://video.google.com/videoplay?docid=7007840369175411712 for those of you not familiar with the yellowbird :)


Thats the video that got me hooked on the ring, love that place - theres nowhere else like it in the world!
The car ain't too bad either :D

That Cairns 911 is looking the bus' - love tough aircooled 911s:ninja:
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posted on December 6th, 2007 at 06:20 PM



I like the new F VEE 1600 front suspension setup it would be an easy conversion for both K&L or balljoint beam make for a very tunable setup maybe with tube arms aswell! by the way awesome project youve got on the go!



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posted on December 7th, 2007 at 05:18 AM



Quote:
Originally posted by mactaylor
I like the new F VEE 1600 front suspension setup it would be an easy conversion for both K&L or balljoint beam make for a very tunable setup maybe with tube arms aswell! by the way awesome project youve got on the go!


Have you got any pics or specs on the new vee set-ups, Mac?

Cheers.
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posted on December 9th, 2007 at 07:12 AM



sorry cant find any and cant remember where i saw them check fvee.org.au. Basically they remove the torsion bars and use thru bolts on the bottom tube then cut out approx 100mm in th middle of the top tube the fab up some bell cranks to link outer arms with some coilovers that lay flat mounted central. it might seem like a lot of work but the weight savings that could be had and the moving of weight to the centre is allways an advantage!



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posted on January 4th, 2017 at 07:04 PM



In selecting coil-over spring rates for your Beetle there are a few things that you will need to know first.
What is the front and rear axle weights?
Example, my modified 1972 Superbug road car (very heavy car due to extras fitted, ie sound system, sound deadener, turbocharger, water-to-air intercooler, suspension mods, etc) has 970lbs on the front axle(43%) and 1280lbs (57%) on the rear axle. This is with me, a full fuel tank, spare tyre, tool box and spare parts bag (my normal driving weight).
Then you will need to know the ride height or suspension travel that you want to use. Example, a near standard height with 6in of suspension travel, or lowered with 3in of travel.
So then you divide your axle weight by 2 (485lbs for my example) to work out the weight on each wheel. Now you know how much weight the spring has to hold just to stop the car from sitting on the ground. With my Beetle I am using QA1 225-475lb/in variable rate 8in coils. These springs have a consistant 225lb/in rating for the first three inches of compression and then stiffen considerably for the next 2in. So when my front end is lowered to the ground from a jack, the front springs only compress 2.15 inches. Then I have another 2 inches before the bump stops. So those 4 inches will take 1000lbs to compress with my variable springs and vehicle weight.
So if your car front suspension weighed 485lbs (per wheel) like mine, and you only had a total of 4in of suspension travel, and you were using 130lbs/in coils, then the suspension would first settle 3.73 inches. And then you would only have a 1/4in left before the bump stops and those 4 inches would have taken 520lbs to compress.
So with these two comparisons, you can see that my suspension is only twice as stiff (to compress the 4 inches) as the second example but I have nearly 7 1/2 times more travel before the bump stops.
If you want to use the light 130lbs/in springs, then you will need long travel springs and maybe a few inches of pre-load.

Hope this helps people understand why different Beetles can run such different spring rates with success.

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posted on January 5th, 2017 at 02:45 PM



9 and a bit years ago but I am looking at it too!



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