rear toe

[pfc]

now that I've crash tested my alignment, it's timely to ask for help! What suggestions based on experience can anyone give me about rear toe-out on A2 cars?
I'm pretty clear about how much is too much.
Phil


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[racer_tim]

Phil, I've always been told to aim for zero toe, with about 1 degree negative camber. That's for an A1 car. How much toe were you running to consider that too much?

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Tim Linerud
San Francisco Region SCCA
#95 GP Wabbit (Bent)
http://linerud.myvnc.com/racing/index.html

[This message has been edited by racer_tim (edited October 20, 2003).]

[Bildon]

There is no 1 right answer here.
For long fast tracks, 0 toe.
For enduros, 0 toe.
For short tracks with tight turns, 1/8-3/16" out....season to driver's taste.

Driver's style, ltd slip, thrust angle of your bent bunny, type of tire, all factor in.



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Bill Sulouff - Bildon Motorsport (http://www.bildon.com)
Volkswagen Racing Equipment
## 2002 ITB NYSRRC Champs ##

[evanwebb]

I don't want to hijack this but I'd like to ask a related question: I am running about 3/16" of toe out on my A1 scirocco to get the rear to rotate a little better, but I know I have a pretty small rear bar on the car. If I go to a larger rear bar can I run less toe-out and still get good rotation? Is there less drag on the tires with zero toe compared to 3/16" out and if so how much difference do you think that would make? Thanks!

[Joe Craven]

I run 1/8" toe out with 1.5 deg neg camber in the rear of my A1 GTI.

500 fronts - no front bar, -3deg camber
350 rears - stiff rear bar -1 camber

Front tires - Goodyear GSCS - 38psi
Rear tires - Toyo RA1s with - 55psi

The car with the above configuration has proven to be very fast at Thunderhill raceway, within .3seconds/lap of the fastest ITB car last event. It's difficult to drive at speed though, very twitchy at the limit and the tail hangs out in the corners. I spun in qualify and nearly lost it in the 1st lap of the race. I find that this is fast though and I do not have to lift off the gas to get the car to turn in. The inside rear wheel is still lifting off the pavement so I'm not sure if more rear bar will help.

#37

Good luck.

[racer_tim]

Like what Bill said, depending upon what kind of tires your running, any toe out and/or in is causing additional friction.

I would start out with a little, and then keep on adding until you've gone too far.

Also depends upon your driving style. You can also adjust for rotation by spring rates, sway bars, weight, etc.




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Tim Linerud
San Francisco Region SCCA
#95 GP Wabbit (Bent)
http://linerud.myvnc.com/racing/index.html

[pfc]

sorry to lag in responding-setup is 600# frt, 400# rear, no frt bar, GTI axle beam, 19mm R bar, and 10" of rear beam boxed.
without changing rear toe, this was a pretty neutral setup; prev I had 345# rear springs and car would get pushy.
when I measure toe, I measure from sidewall apexes which is a 19" base.
unmodified, car had .400" (whew!) rear toein, evenly split. I set it at .070" (total) out. I figured this was fairly conservative. This netted a nearly undriveable car when turning/braking.
I was amazed at how profound this change was and have many questions. I only got one session in before crash, but was suprised to see that frt tire temps were 40* higher than rear despite wicked oversteer. What happens if I soften rear? did I just have too much toe-out? some say they run much more toe out.
Regarding question about friction losses-I've experimented with frt toe in coast down tests and found that anything more than +/- .080" toe clearly slows the car down faster.
Bill-what is a tight twisty track to you?
Phil


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[Joe Craven]

Phil, my car had a lot of toe in too which I adjusted out. The 10" of box section (isn't this illegal?) in addition to the rear bar has probably made the rear roll stiffness too high. The previous toe-in with the roll stiffness probably made the car about right for your tastes.

Now that you've corrected the rear toe-in condition, you might have to reduce roll stiffness. You might try removing the 19mm rear bar and try it again at slow but increasing speeds in a test session. I'd leave your toe out where it is (reconfirm it though) or reduce it back to zero. I've raced my GTI with over 1/4" rear toe out (bent beam) which is absolutely hairy.

#37 ITB

[pfcs]

Joe-again, how are you measuring toe? so we compare apples to apples.
thanks for response-I'm just a little confused about this stuff. If the car was fairly neutral and generated sensible temps, how can it work to lower rear stiffness/couple? My intuition says I've got too much rear toe-out. Or is it just that FWD is so different in setup than what I'm used to-that maybe you can't ever fully use the capabilities of the rear tires w/FWD-that you resort to counterintuitive solutions to band-aid/coverup the problem that with FWD, the front tires are ALWAYS the limiting factor! Please enlighten me.
Regarding the flat stock across the beam, I consider it to meet the definition of an anti-roll bar per GCR glossary. Comparison with a stock 240 volvo rear bar in the context of the definition is helpful. And, it sure didn't cost much! The old Bilstein Rabbits used to put a section of 2"(?) square tubing in the middle of the beam with 2 large "U" bolts which could be adjusted laterally to change the effective rate. I was going to do that but the GTI swaybar in the channel of A2 beam interferes.



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phil hunt

[Joe Craven]

I measure the rear toe the same way I measure front toe. I put two plates across the side of the tires and I measure the distance in front and the rear of the tires. The difference is toe out or in.

I don't think it is legal to modify the beam to change it's properties. You can probably weld sway bar mounts and I think there isn't much more than you can do. The Bilstein Rabbit example you gave would be legal because it is a bolted on sway bar.

You described that your car was neutral handling with a lot of toe in. If that is the case, it will turn faster even with zero toe in the rear.

In regards to FWD, I think the early A1 Rabbit at least seems to be limited by the front tires. I've been unable to make my car neutral so I put better tires on the front and purposely reduce traction in the rear. My car went as fast as any ITB car last weekend in all of the corners so I can't say that I have a handicap. I just need more power!

#37 ITB