Poppy's Vette

Who can tell me what the diameter for the 18x8.5 fronts wearing the 245/40 run flats and the 19x10 rears wearing the 285/35 run flats is?

The way I work it out the OEM fronts are 25.7 and the rears are 26.56. That would make the rears taller by .86"

I'm working on a set of track wheels and tires and am interested in how close these will be since I'm going to run 18" wheels on all 4 corners. The track combo I'm working on will have a diameter of 25.1 front and 25.5 rear. That makes the rears of this setup taller by only .40"

That seems close enough to me (less than 1/2 inch) but I don't know how close the tolerences built in to the system are.

Any thoughts?

TIA - Paul

AU N EGL

The rear only needs to be slightly larger then the front. That 1/2" is fine

Poppy's Vette

I actually used the wrong size to figure the stock rear diameter. It's actually 26.9. So now it's a 1.2" difference instead of only .4".

I wish I could find something written up on this. Heck, I can't even find what the results of mismatched wheels & tires would be?

AU N EGL

.4 is fine, as long as the rear wheels are larger then the font.

There are severl guys who run the same size wheels front and back. turn AH & TC off and they have no issues.

The 18 -19 " stagared wheels size is just for costmetic, not performance.

The compter only needs to know the rear is larger, rotating slower then the front.

gkmccready

Tom, I thinks it's safe to assume that folks asking this question are only concerned because they want to run with AH/TC or Comp Mode or run dual-purpose street track (and not have to remember to turn everything off all the time).

pcervone, this topic is almost as much fun to dig up C6 details on as tire pressure sensors. :-)

Poppy's Vette

I hear ya. I think I've read most everything I could find but it never really gets to an answer I want to hear. I have no issue with buying a set of TPSs and calibration tool for the new wheels. That's a no-brainer as far as I'm concerned.

And, I don't intend to run with AH/TC on. I was assuming I might run in Comp Mode but not necessarily. Are you saying these concerns are moot if I run with everything shut off?

UberR32

OD_tire = 2*((profile/100) * width) + OD_wheel

e.g., the rear OD is:
2*(35/100)*285+19

Try to keep the ratio of the front/back diameters as close as possible to stock, and the computers will be fine.

rudyarias

I went to running 295/35R18 front & rear since upgrading to bigger brakes/14" rotors and have had no issues with and without A/H on the track or street.

gkmccready

On a C6?