I'm sure this has been covered, I tried a search but nothing had any real answers.

What affect on the VDC system does changing the wheel size have? I read that you need to stick with the same overall diameter to not affect the VDC, but I see guys running sizes that are not the same diameter as OEM.

 

Wheel sizes wont affect the VDC. However, having the incorrect tire sizes/wrong outer tire diameters from front to back will cause issues.

 

thats what I mean . I know the wheels themselves wont affect it, but depending on wheel/tire combinations, the overall diameters can be larger or smaller. I know there are guys out there running different that stock diameters, what are they doing about the VDC? Even running with it turned off, it will still detect slip.

 

VDC will only really act up when the front tire circumfrence is larger than the rear. Even with equal circumfrence tires front and rear, I've found that the VDC rarely intrudes.

 

From what I can tell, the VDC detects changes in the wheel rotation. If one wheel slips (in the snow or ice or something) the car will try to compensate and prevent further slippage and, ultimately, a spin-out/lose of control. So, if you change tire sizes, the wheels are rotating at a different rate, the car will keep trying to compensate with the VDC kicking in. I noticed this when I went to my current wheel/tire setup, my overall diameter changed a bit. When I drove the car for the first time, the SLIP light came on and the car freaked out for a few feet. Then it stopped and has been fine ever since. So I guess the car "learned" the rotation rates of the wheels and adjusted for it. That's my understanding and experience. I hope that helps.

 

For the coupe, you just have to maintain a ratio as close to the stock diameter difference from front to rear. The stock 17's have a 1.5% difference, 18's have 2.7%, 19's have 2.4%. I'm not sure about the sedans.

Basically, anything between 1.5% through 2.7%(for the coupe) would be the ideal ratio(the rear always being the bigger diameter). I've seen ratios beyond 1.5%-2.7% but I'm not exactly sure what the limit is until VDC starts to get real sensitive.

 

I want to change my wheels and tires on my '03 6MT coupe to 4 of the same size/offset, in order to be able to actually rotate them. Does this present a VDC problem?

 

Outside tire diameter is the key. Does not matter what the tire is attached to as long as the front/rear diameters are staggered correctly. You can't put the same sized tire front/rear on the car or the VDC will have issues.

VDC issue threads

https://g35driver.com/forums/wheels-...-question.html

http://myg37.com/forums/brakes-suspe...-now-this.html

http://my350z.com/forum/wheels-and-t...lip-light.html

 

As long as the overall diameter of the tires are close (front and back), you will not have any issues. The below link is a good tool for figuring this out.

http://www.miata.net/garage/tirecalc.html

 

ok, now my next question is this, more so clarification...

so it doesnt matter the overall tire diameter, as long as the difference from front and rear are close to the stock differences?

For example, lets say stock is 26.5"/front, and 27"/rear, but the new setup was 28.5"/front and 29"/rear... since the difference from front to rear is the same as stock it should be fine?

I understand the speedo is going to be off with a different overall diameter ,not concerned about that. Just dont want the VDC acting up.

 

Yes exactly, here... use this
http://www.rimsntires.com/specs.jsp

 

ive been doing some research but was wondering if running a 245/35 F and 285/30 R tire combo would throw off the vdc? or should i just stick to a 275/30 in the rear?