sffish

I've got a '98 Coupe and want to get larger fronts to help reduce the understeer in the car. I'm running the Kumho MX's in the stock sizes right now. I want to get either the 255-40-17's or 255-45-17's (as opposed to the current stock 245-45-17's on the car) to help get more grip in the front. Which aspect ratio should I get, 40 series or 45 series?
Doing the math the the stock sidewall is 110.25mm while a 255-40-17 has a sidewall of 102mm and a 255-45-17 has a sidewall of 114.75mm. Should I get the 45 series and raise my front ride height or get the 40 series and reduce the front ride height. I've got the car lowered using the stock adjusters both front and rear. Thanks.

VetteDrmr

I'd go with the 40 series tire.

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Go with the 275/40/R17 tire. That'll get rid of your understeer and put you into a slight oversteer condition (at least it did for me). You'll also get better braking.

Yes, you can run that size tire on stock wheels: I've done it for over 2 years. No, there's no tire wear problem. In fact, I think that, for autocrossing purposes the tire wear is just about optimum.

Yes, you'll have people yelling at you that your "contact patch is compromised." Ok, maybe so. You're still getting more grip than from a 255 series tire.

HTH, and have a good one,
Mike

TedDBere

I'd go with the 40 series. You'll increase your tire width and drop the front CG, both of with will reduce understeer.

StArrow68

I run Z06 wheels on a coupe and have the 275/17 mentioned above with the 295/18 in the rear and it is superior all around. I don't see anywhere near as much understeer and with only coupe power I really don't have much to worry about with oversteer. At the track it seems pretty bullet proof.
BTW, did I mention that I get to use all the contact patch all around!
randy

VetteDrmr

Yeah, I was thinking about recommending the 285 width tires for the rears (assuming you want to stay with stock width wheels), but I figured on getting the understeer problem fixed first and see how he liked that setup.

Have a good one,
Mike

Cobra-R

Is this autoX or high speed open tracking? You could always try moving your apex's later and/or trailbrake(depending on whether the understeer is at turn in or track out). I used to have huge problems with understeer in my Cobra, some of it was setup, most of it was driver.

I have limited tracktime in my vette, but compared to my Cobra, it doesn't understeer bad at all.

Brian

sffish

Car will be used for a little bit of auto cross, but mainly daily driver and open tracking. I just want the car to be more neutral while keeping the stock wheels. I had a 944S2 before and it was about perfect mid corner. Just a little understeer, but capable to inducing lift throttle oversteer in a medium speed turn. I can't do that with my coupe.

Cobra-R

Have you played with your lines, that will make a huge difference. Try and get a more experienced vette driver to ride with you, maybe a little line tuning is all you need?

If you need new tires, I certainly would buy the wider, just trying to throw some idea's at ya.

Brian

yellow01

I run 275/40 in front and 295/35 in back and love it.

silverz06vette

I don't have to much understeer with 275s up front and 335 on the rears.

710s.