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JoElla
08-10-1999, 06:29 PM
<br>1999 Mcoupe came shod from factory with 225/45 ZR 17 light alloy wheel 7.5 J x 17 ahz; 245/40 ZR 17 9.0 J x 17 ahz;<br> [ahz=asymetrical hump] keeps that ole flat tire on the rim so you can really trash it on the way to civilization!<br> On quest to tame the understeer and to find available track tires that last more than two events I was advised by Tire Rack to try Yokohama 032s 235/40 17 F & R "lots of the guys are doing it to tame understeer".<br> Synptoms: Lots of tail wag on braking in straight line farom 90+ down to 40 for a turn on a raod track circuit.<br> Theory: The Mcoupe is set up with brake bias based on wider rear tire and narrower tire in front; NOW we have wider front and narrower rear..therefore, too much brake up front and not enough in rear [Mcoupe has no downforce anyway]. <br> Solution? change pads to PFC 80's on front and 90's on rear to compensate the break bias problem???? what do you guys think?<p> I will return to factory set up on tire size as soon as these yokohamas wear out. In the meantime I'm bound for Kershaw in 2 weeks and need some good advise. Thanks, JoElla<p><p><br>

dp
08-10-1999, 07:02 PM
actually, it seems the brake bias is set up for the 'proper' sizing (based on rim width) of 225/45 front and 255/40 rear (instead of cost-cutting use of 245/40 from M3 on the back). i say this because when i switched to the proper tire size, brake dust now collects at roughly equal rates front and rear on the track, as opposed to heavy front bias on stock tires. i find that the understeer is not a problem with 225/255 setup (i use bfg g-force kd's) as long as you keep tire pressures same or slightly higher upfront. also getting on the power right at turn-in helps. the coupe doesn't like trail-braking, in my experience. this thing is more like a superbike - brake, flick, power. with my setup all the instructors and passengers that have ridden with me at track events have been impressed with how neutral the car is and how well it behaves under threshold braking (i never get into abs, but it's always very close) - so much so as to offer unsolicited praise ;)<p>i did find that i get a lot of wear on the outside of the front tires, so the REAL solution to understeer might be getting some more camber upfront. my guess (and this is only a guess) is that the us versions probably ride 1/2" or so higher in the front than european to meet headlight/bumper height standards (i know this is true of some cars, don't know if it's true of the coupe). that would explain the camber issue. anybody have definitive data on that?<p><br><i>: <br>: 1999 Mcoupe came shod from factory with 225/45 ZR 17 light alloy wheel 7.5 J x 17 ahz; 245/40 ZR 17 9.0 J x 17 ahz;<br>: [ahz=asymetrical hump] keeps that ole flat tire on the rim so you can really trash it on the way to civilization!<br>: On quest to tame the understeer and to find available track tires that last more than two events I was advised by Tire Rack to try Yokohama 032s 235/40 17 F & R "lots of the guys are doing it to tame understeer".<br>: Synptoms: Lots of tail wag on braking in straight line farom 90+ down to 40 for a turn on a raod track circuit.<br>: Theory: The Mcoupe is set up with brake bias based on wider rear tire and narrower tire in front; NOW we have wider front and narrower rear..therefore, too much brake up front and not enough in rear [Mcoupe has no downforce anyway]. <br>: Solution? change pads to PFC 80's on front and 90's on rear to compensate the break bias problem???? what do you guys think?<p>: I will return to factory set up on tire size as soon as these yokohamas wear out. In the meantime I'm bound for Kershaw in 2 weeks and need some good advise. Thanks, JoElla<p><p></i>

M Sipe
08-10-1999, 07:43 PM
Are you sure they understood you had an M coupe and not a Z3 coupe? There's absolutely no way you'll solve your problem without going to a wider rear tire; preferably a 255/40 rear size for an M coupe. Certainly no less than the factory 245/40.<p>I'd call the Tire Slack manager and seriously complain because if they knew you had an M coupe then they screwed up recommending 235/40 rear tires for an M coupe. This is not the way to tame understeer on this car, especially on Yoko A032R's, which aren't more than good street tires IMO.

Bruce
08-10-1999, 10:22 PM
i had a set of A032Rs 235 front 255 rear on my M roadster. I have tracked it 3 or 4 weekends with no complaints. BUT, I drove one session in an M roadster with Kumhos- if I kept the wheels the Yokos would have been history, the Kumhos are awesome and I hear they last almost if not just as long as the yokos.

dp
08-10-1999, 11:33 PM
<i>: Are you sure they understood you had an M coupe and not a Z3 coupe? There's absolutely no way you'll solve your problem without going to a wider rear tire; preferably a 255/40 rear size for an M coupe. Certainly no less than the factory 245/40.<p>: I'd call the Tire Slack manager and seriously complain because if they knew you had an M coupe then they screwed up recommending 235/40 rear tires for an M coupe. This is not the way to tame understeer on this car, especially on Yoko A032R's, which aren't more than good street tires IMO.<p></i>

Koby
08-12-1999, 10:49 AM
I agree with all that has been posted on the topic thus far. From what I understand, and from my experience setting up cars for the track, there are a few fundamental problems with the suggested 235 F/R setup. (1) As fitting a car with same width F&R will tighten the steering curve and response, it is done at the cost of stability if the design of the vehicle is for wider rears. (2) Several other components of the set-up can be adjusted to resolve the understeer problem ONCE THE TIRE SIZES are RETURNED TO FACTORY SIZES. Returning the setup to OEM is the best place to start. As mentioned by another reader, the ride height in the front may have been forced upon the OEM setup to pass US Bumper regulations.... so this would be a good place to start. Furthermore, increasing the stiffness of the front suspension will also have the effect to reduce understeer. Other modifications that can be considered include, but are not exclusive to: Suspension stress components for the F&R, Camber adjustments for the front (reduce)... etc.<p>I hope some of these suggestions are of use!!<br>Koby<br>

Koby
08-12-1999, 10:52 AM
I agree with all that has been posted on the topic thus far. From what I understand, and from my experience setting up cars for the track, there are a few fundamental problems with the suggested 235 F/R setup. (1) As fitting a car with same width F&R will tighten the steering curve and response, it is done at the cost of stability if the design of the vehicle is for wider rears. (2) Several other components of the set-up can be adjusted to resolve the understeer problem ONCE THE TIRE SIZES are RETURNED TO FACTORY SIZES. Returning the setup to OEM is the best place to start. Through the process of elimination, the source of the understeer can be located. As mentioned by another reader, the ride height in the front may have been forced upon the OEM setup to pass US Bumper regulations.... so this would be a good place to start. Furthermore, increasing the stiffness of the front suspension will also have the effect to reduce understeer. Other modifications that can be considered include, but are not exclusive to: Suspension stress components for the F&R, Camber adjustments for the front (reduce)... etc. If all else fails, then try to compensate by increaseing the rear tire size (by doing that first, a whole new can of worms is let out!).<p>I hope some of these suggestions are of use!!<br>Koby<br>

Koby
08-13-1999, 05:07 PM
Correction... Suspension adjustments mentioned in the earlier post should be done ot the REAR suspension and not the FRONT. My mistake.


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