inflectionpt

After owning the C32 since 2003 and with only 72k miles, I've decided to turn it loose for a few track events and have some fun. I've read numerous threads regarding handling of the C32 and it's tendency to understeer. I also read that the understeer can be reduced by destaggering the tire/wheel setup. I recently came a cross a set of the c32 rear 17x8.5 rims and purchased them. From all the information I could gather, it appears that 245/40/17 is a good for the destaggered setup. I've read that 245/40/17 on the rear rims will fit in the front. What I want to know is will I need to roll my fenders in order to accomplish this?


Just want to make sure since the track event I am going to is coming up the day after Christmas (Thunderhill) so need to order tires now. I plan on getting the star specs as my track oriented tires.

Thanks.

kent426

There are numerous things that can cause understeer and can fix it without eliminating forward traction. If you destagger, you will end up with a drift car and go slower.

Your springs or tire pressures may be the cause. I run KMac bushings upfront with 1.5 degrees negative camber and have a car that oversteers, I can dial that out with tire pressure but I react better to oversteer than understeer.

inflectionpt

How's the ride with the kmac bushings? I know that will give you a lot more control in terms of suspension setup but my intent is not to setup the car with harsh ride.

splinter

Yup, many here have swapped OE AMG 17x8.5 34 ET wheels up front. Gleaned that understeer-reducing upgrade from this forum years ago.

Verify proper 245/40/17 clearance before getting after it. My current Michelin Pilot Super Sports are quite close to the MacPherson struts.

inflectionpt

I guess I just have to get the tires (thinking star specs) and see if they fit.

reserved

MB's (like many cars nowadays) have HUGE amounts of understeer built into the design, not because of the designers, but because of lawyers!!!!!!!

Going to a square set-up is really step #1 to deal with that, which is why most dedicated track cars (with the exception of the Porsche guys) are set up that way.
It is also very helpful as you can rotate your tires very easily (assuming you are running a clockwise road course, that driver-side front tire really takes a beating!).
Regarding tires, I think the Star Specs are a great choice - very grippy (for a non R-comp tire) and last a long time.

Good luck and have fun

kent426

No negative ride impact noticeable from the bushings, they are great quality and will easily outlast two sets of rubber.

The biggest ride quality degredation I got was going to extreme dry tires but that is something I can live with :-)

kent426

I am sorry but that is the worse advice I have heard in a long time. Mercedes are under-tired from the factory. 245 rears are no where close to what these cars need. 275's are barely adequate. 235's are about perfect for the fronts. The most important factors that dictate handling characteristics if you read any road racing books is: tires choice, optimal contact patch. Not all tires react in the same manner when it comes to cornering. Contact patch is dictated by camber, spring rates, weight distribution, tire pressure and roll stiffness.

To run at the track with street tires, tire pressure needs to be increased significantly to prevent the sidewalls from rolling over. Next to solve balance issues, the rears can be slightly over or under inflated to dial some of that out. These is the no dollar fix.

The next best dollar fix is with dialing in negative camber, marking your tires and observing the wear pattern under hard cornering to determine if you have an optimal contact patch.

Need I say more?

reserved

OP: As you see, there can be differing opinions!
I suggest you research on other forums where people actually use their cars for driving on track. The M3 guys are probably a good source. Example:

http://forum.e46fanatics.com/showthread.php?t=729224

Again, conventional wisdom is that in cars such as MB, BMW etc., a severely staggered set-up (like 235F/275R) will exacerbate the understeer issue. It will make you slow in turns because of "push" and therefore slow on track.
BTW, I am not an expert by any means. I have just tried to learn from others in the 50 plus track weekends I have attended in the past 3 and 1/2 years.
Let us know which direction you take!

kent426

So that is one quote? Cars with low hp/ low end torque don't need a staggered set up. Cars that win races are the ones that are able to put the power to the ground soonest coming out of a corner, not all out corner speed. Read the last edition of Grassroots Motorsports interview with Randy Pobst to understand the difference between a low HP car (a miata) and a high HP car (viper). Tell me if you see any super cars with a destaggered set up too while you are at it.

And in case you think I am just a street punk, you can see my posts

http://youtu.be/x3CQsaTUNsw

I've got plenty more autox posts if you would like too.