VW A1 GTI shock/spring question

J

Joe Craven

New member
I'm thinking about converting my NASA GTI Cup to ITB specs and racing it as my primary car. I want to make this car much faster with as little money as possible. It's currently a mid pack ITB car, about 2 seconds off the pace at Sears Point and Laguna, and 4 seconds at Thunderhill due to the effect of lack of HP. I think the suspension is the weakest component of the car right now. The GTI Cup requires open diff, spec springs and shocks among a few things. I've taken apart one of my spare struts and the front springs seem about 1/3 as stiff as 300lb/in springs. They might be 100 to 150 lb/in.

The strut cartriges are Bilstein yellow sports. Fronts are P0032 and Rears are B0657

How stiff of a spring can I safely go with these off the shelf shocks. 300lb front and 200lb rear? Can I get these shocks revalved so I can run higher rate springs like most other VW racers?

I would also like to eliminate the open front diff traction problem. I'm ok with squirley and difficult to handle cars. I'm thinking that welding up the front diff might be the cheapest/fastest way to improve corner traction under acceleration.

Thoughts?

#37 ITB Capri and GTI.
 
I've tried 300/200 and it seemed pretty soft but car drove great. Front and rear Neuspeed sway bars installed. As Tim mentioned, this would make a good rain setup. I was able to turn 2:03s at Sears on these springs with Toyo tires.

This Sunday, I ran the GTI with 500/350 with and w/o the front sway bar.
Front camber, 3 deg and 0 toe.
Rear camber , 1.5 deg and 1/16 toe out.
I raised the fronts to get the A-Arms close to horizontal.

I put on Goodyear GSCS on the front and kept Toyos on the rear. The car was stiffer but I still wasn't any faster. This perhaps makes a good point that stiffer isn't necessarily faster. Anyways, I'd like to get the car to oversteer more so I know many of you are running two rear bars. What bar would you suggest in addition to the Neuspeed bar? Or should I just keep one? Here is the link to my bar.
http://www.neuspeed.com/products/product_d...s_euro&p_id=248

Thanks- #37 VW GTI Joe Craven
 
Joe, from the ol' Team T/A Pocket Guide, to decrease understeer:

Lower front tire pressure
Raise rear tire pressure
Larger front tire section
Smaller rear tire section
More front neg camber
Less rear neg camber
More front toe out
More rear toe in
More front caster
Softer front springs
Stiffer rear springs
Smaller front sway bar
Larger rear sway bar
more rear weight distribution

Since you've already tried the springs, and you can't really adjust caster, I'd go for taking out the negative camber in the rear, work with the pressures, add some front toe out, and take out the toe in the rear.

It also looks like you changed too many things for this outing. No front sway bar, springs, and GoodYears instead of Toyo's. Wasn't it also much warmer this weekend @ Sears than when you ran the car on the softer springs and Toyo's?

The key to troubleshooting is to only change 1 thing at a time, and test it out. If it didn't work, change it back, and try the next thing. Changing too many things, and you can't tell which change worked or didn't.

P.S. Let me know when your testing next, and I'll bring the doorless Wabbit out to compare against.


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Tim Linerud
San Francisco Region SCCA
#95 GP Wabbit (Bent)
http://linerud.myvnc.com/racing/index.html
 
Hey Tim, the temp difference is a good point although temps were much lower on Sunday.

In general, I've been able to balance my GTIs handling by decreasing the traction in the rear by using rear toe out nad either using full tread Toyo tires or pumping up the rear tire pressure to 60psi.

I made two different test runs.

1) Toyos on front and rear 500lb front, 350 rear, front and rear sway bar installed.

-Car handled as before although stiffer with less body roll. Car understeered with rear tires at 40psi

2) fixed excessive rear toe, removed front bar and installed Goodyears on the front. Car drove a little different but seemed about the same as above. I was able to go about as fast as before but I was hoping that the rear would rotate better, i.e. more oversteer w/o having to reduce rear traction.

My goal in car setup is to optimize front and rear and get both ends to stick as best as possible. If I can us rear roll stiffness to improve balance, that would be my preference.

#37 ITB VW GTI
 
Tim, my next session will be at the next regional SFR event at Infineon (AKA Sears Point) Raceway July 12 and 13th.

Since I will only get 1 practice session before the qualify, I think I will only change the front tires for fresh Goodyears, rears with the old Goodyears and basically keep everything else constant. I might install some additional rear roll stiffness if I can find some box tubing like Bildon suggested. Where can I find some 4x4 tubing - Home Depot?
 
Joe,

I don't think the stock-valved Sports can handle the 500# springs up front. The car may feel stiffer, but I imagine that it might be a bit skatey.

I would add another rear bar. My old car had a Shine-style bar, and a BSI-style bar.

You mentioned getting the front A-arms level, but you don't talk about your rear ride height. I used to run my car 1/2" to 3/4" lower in the rear than in the front. You might also want to try 1/8" toe out in the rear.

------------------
MARRS #25 ITB Rabbit GTI (sold)
SCCA 279608
 
Bill, I was wondering about the shock issue but I haven't noticed anything obvious like worn out shocks. I was running on a front set of used Goodyears so maybe they just weren't any good. However, I did run the practice session on good Toyos but the rears had 1" toe out which I later reduced to 1/16". It was definitely skatey with the 1" rear toe out but once the car took a set in the corner, it seemed fine and understeered a tiny bit like usual. Inside rear wheel was off the ground as normal.

Since I have more time at home (rather than at track adjustments), I'll try increasing the rear toe to 1/8". What do you think, another 1/64" shim on each side? The rear was set lower than the fronts and I can lower it another 1/2" which I'll do and corner weight too.

Funny thing is that even though I disconnected the rear bar, the car seems to have the same amount of front wheel spin in the corners. I have an open diff which I plan to probably weld up after I sort out these suspension changes (As Tim suggests, I'm already changing too much at once).

People following me are reporting that the inside rear wheel isn't lifting as far as before and car is leaning less. My tire temps are still about the same although the Goodyears have me a bit perplexed. I'm getting slightly higher readings in the center (pressures mid 30s) but I read that others run them in the 40s.

Bill, question on the bars. Since my VW is already lifting an inside rear wheel in the corners, does adding a second rear bar help much? As I think about it, perhaps it does by reducing rear wheel suspension travel and reduces the weight transfer to the outside front wheel.

#37 ITB VW
 
Joe,Let's try again.I run springs at 500 front/600 rear, shocks are revalved Bilsteins to match,no front bar,a Shine and a Chevy Caprice rear bars,front 1/8 toe out, 2.5 deg camber and rear at 1/8 toe in and stock camber. Car still pushes a little.
Warren

[This message has been edited by Dead Skunk (edited August 18, 2003).]
 
I have stock Bilstein sports, with GC camber plates, 500 lbs up front, and 300's in the rear. Running a 1" bar up front with a Neuspeed rear bar. 1 degree neg camber front and back, with 0 toe front and back. Locked front diff with 3.94 r/p.

20x8x13 slicks up front and 20x7x13 slicks in the rear. I don't have a push problem with this setup.

When the front tires go away, then it starts to push, but that was when I corded my fronts during qualifying @ Rose Cup. Didn't really have a chance to race with new (used)Hoosiers up front.



------------------
Tim Linerud
San Francisco Region SCCA
#95 GP Wabbit (Bent)
http://linerud.myvnc.com/racing/index.html
 
>> 500 lbs up front and a 1" bar up front

eek.gif
So your front wheel rates are thru the roof.
Have you unhooked your front bar and really felt that the car was worse?

Sounds like you should put the 300# on the front and move the 500# to the rear to hold the nose down instead of using the big front bar.

Unless you are an ex-linebacker for the 49'ers and have a lot of front weight bias...then the bar would make sense.

What's you F/R and LR/RF corner weight % like?

I'm curious as I haven't known may to make your setup work. But I know you've been racing a long time and I imagine it is working.

- Bill
 
What's you F/R and LR/RF corner weight % like?

LF 682 RF 637
LR 403 RR 375

Total was 2,097 lbs

Front Weight 1,319 @ 63% of Total
Rear Weight 778 @ 37% of Total

LF to RR Cross Weight 1,047 lbs @ 49.93%
RF to LR Cross Weight 1,050 lbs @ 50.07%




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Tim Linerud
San Francisco Region SCCA
#95 GP Wabbit (Bent)
http://linerud.myvnc.com/racing/index.html
 
I've watched Tim race his Rabbit at Laguna Seca and it appeared to be well balanced in the corners.

I'll be racing my VW this weekend with the following.

Front springs 500
rear springs 350

no front bar, 0 toe
Neuspeed rear bar modified with additional angle iron welded to it. 1/8 toe out.

I only had a few laps last event to test this out and I almost crashed the car when I spun out on the warmup lap. VW seemed to handle ok once the tires reached temp.

Luckily, we have 2 practice sessions in group 5 this weekend. I will probably need them and more.

#36 ITB VW
 
The following has worked very well for me in a Scirocco:

650s front, 425s rear, revalved Bilsteins, no front bar, big hollow Shine (SRS) rear bar. I used to run 400s in the rear plus a second or third rear bar of varying sizes, but decided to save a little unsprung weight by upping the rear springs and nixing the second/third rear bars. Lost some adjustability but handles better, even on ice
wink.gif
 
Thanks guys, car handled great although there are a few other deficiencies.

open diff - I was getting lots of inner front wheel wheelspin in 3 of the slower corners. I could see my competition pull away in those corners.

horsepower - I finally got the car running correctly (settled on 35 deg timing as suggested by Tim) but I'm way down on power as compared to the ITB class front runners. I need 10 to 15 horsepower!, not sure where I can legally get it.

I was a little over 2 seconds/lap slower compared to the fast BMWs.

I think I'm going to try a welded locker and see what I need to do after that.

#37 ITB VW - at least it made the weekend in one piece and still running.
 
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