: Kind of a specific tire question... i know, boring.



ImEpayne
07-15-13, 09:18 PM
Hello all. '06 CTS-V and well... my rear tires are bald. Heh

Here is the situation. I have changed over to the STS-V staggered set of rims: 18's in front 19's in back. I am running 275/40/19's on the rear. Found a retarded deal on craigslist for a set of (4) Michelin Pilot Primacy's (any feedback?) I am not worried about the rear as I am running no spacers on the wheels and buying the same size tires. So rubbing won't be an issue. My concern comes with the fronts. I don't quite need fronts yet but might as well do them while its on the lift. Currently I am running 255/45/18's on the front. With the STS-V rims I had to put in a 5MM spacer so that the tire(if I'm remembering correctly) wouldn't rub on the upper control arm. But the 45 sidewall just looks gigantic and bubbley...

My questions is: if I drop down to a 255/40/18, do I run the risk of rubbing again?



Thanks everyone
Eric

Andringa
07-16-13, 11:05 AM
What do you mean by " But the 45 sidewall just looks gigantic and bubbley..." ?

I think that you might want a narrower tire, not a shorter tire.

The stability control system in our cars assumes 4 tires with the same outside diameter. (It uses revolutions per second to calculate wheel speed.) Because of the stability system most people on the forum suggest keeping the difference in overall height of front to rear tires less than 3%. I think that going to a 255/40/18 would start to cause you issues since it would be significantly (6.1%) smaller than your rear tires.

A narrower tire would look less "bubbly" and the stock size of 245/45/18 is only 3.4% smaller than your current rear tires.

According to an online calculator:
275/40/19 = 27.7"
255/45/18 = 27.0" -2.6%
255/45/18 = 26.0" -6.1%
245/45/18 = 26.7" -3.4%

This is all assuming that there isn't a way to tell the CTS-V stability control system that you have changed the size of the rear wheels. Obviously the STS-V was setup from the factory to run different overall tire sizes front to rear and has Stability control.