C43 autocross set-up

I am thinking of getting a 2nd set of wheels/ tires for autocross. I'm going to go with Kymho's but haven't decided on wheel size yet. I'd like to get 17 X 8's and mount 245/45R17's tires but don't think they'll fit up front. I could stay with the stock staggered set-up, but then loose the ability to rotate. I'm not looking to roll the fenders. Any thoughts would be appreciated


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Noah
1999 C43
4Noah.homepage.com

[Lee Scheeler]

Noah,
First off, the 245/45/17's are too tall a rolling radius so that would cause major ABS/ASR/ESP problems. If anything, you would want to put the same size on the front as is on the rear, but I don't think it will fit. The stock setup is fronts running 225/45/17's on 7.5x17's with 245/40/17's on 8.5x17's in back.

Oh, the fenders should already be rolled from AMG. (stock fender roll is 50 degrees, I believe AMG rolls the fenders to 100 degrees. Before you go looking for gonzo wideness in tires, remember your car is already a "tuned" car. AMG has pushed many things pretty close to their limits already.

Kumho's are pretty popular, the BFG R1's had a cult follwing but you may not be able to find any as they have been replace by a non-asymetric version. Be sure to get the car re-aligned for autocrossing. Lots of negative camber up front will help.

Let us know how it goes...Lee

[TommyMB]

Keys to fast time in tight courses: Adjust the front toe setting to toe out 1/16" (or more, but it will be skitish on the road) to reduce initial turn-in understeer. Increase front tires pressure and possibly reduce rear tires pressure to reduce understeer. A good compromise camber setting for a street car are - 1.5 degrees on the front and - 2.0 degrees on the rear. Go for more negative settings if tire life is not an issue but remember big negative cambers will decrease traction in braking and acceleration.

A set of Koni sport setting shocks will do wonder on turn-in also.

[mbdoc]

Have the alignment set for the most -(neg) camber, the most +(pos) caster, & the toe-in as close to 0deg. As the toe goes down the car isn't as fun on the highway, so have it set at .1 or .2 deg. If you plan on running stock class then have the spring pads removed before alignment. The AMG shocks, springs, & anti-sway bars should get the job done. Solo 2 is a lot of fun so enjoy!! Driving skill wins most of the time.

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MERCEDES BENZ MASTER GUILD TECHNICIAN
ASE MASTER TECHNICIAN
27 YEARS DEALER M.B. TECH
190E 2.3 ITS RACECAR

Thank you guys for the guidance. Here are the things i'm considering. The car has to stay streetable. I use it EVERYDAY. I don't have any problem with a harsh ride or nervous steering - but the car has to be usable.

QUESTIONS:

1. will removing the spring pads have any down side? I was told my my dealer that they are 9mm pads.

2. What are the best compromise settings in terms of negative camber, toe, etc... For both autocross and daily driving?

3. When comparing the Kumho 700's with my OEM conti's i found the following. My front tires, 225/45/17 have an actual foot print of 7.75 inches wide. The rear tires 245/40/17 have an actual foot print of 8.5 inches wide. The Kumho's have and actual foot print of 8.66 inches!!! Given this fact, and that i don't want to create ESP/ASR/ABS error, Should i go with 4 tires that kumho calls 225/45/17 but have a true footprint larger than my street 245/40/17's? The specified rim size from kumho is 7.5 wide - which is the size of my AMG RIM up front. If i got 4 AMG wheels, This would keep my rim size, off-set, and quality all up to AMG specs!
What do you guys think?



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Noah
1999 C43
4Noah.homepage.com

[Lee Scheeler]

Noah,
Tire footprint is not what the wheel speed sensors see. What they see is the rolling radius of the tire. (height of the rim plus two sidewalls) As long as the rolling radius is the same on all four corners then things should work fine. The Kumho's probably have a larger "footprint" due the square nature of the shoulder vs the more compromising/rounded nature of the conti's.

Were I setting a car up to race AND street, I know of noone better to have helping with the setup than MB DOC.

You can get a second set of AMG rims that will certainly meet all the quality and appearance issues. A lightweight rim like BBS would also be something to consider provided it meets stock specs.

Hope this helps...Lee