i just ordered some 17x9.5 black zr1 wheels with 275s. my car came with the 235s, and i was wondering about speedometer accuracy. ive read that if your car had 245s or was it 255s? well either way, ive read that if you had the bigger tires from the factory, the speedometer wont be off by much at all with a 275 tire. will i have any problems with the speedometer? i want it to be correct. would my odometer turn faster without fixing the speedometer?

thanks,
adam

 

275 or 245 that is the width of the tire your main concern should be the profile(height)of the tire.if you are using a 275/40/17 it will be ok but if you are using,hmm,275/50/17 that will be too tall....i have 285/40/18s rear and 245/40/17sfront they are from a 99 c5 vette and work nicely....

 

cool, thanks. mine are the 275/40/17s. i thought it would work out ok.

adam

 

i belive each tires should be abou tteh same height as stock , correct me if im wrong

 

The "base" Z28s and Formulas came with 235/15-16 tires. They are 26.18" diameter. If you ordered the car with the RPO "QLC" Z-rated tires, you got the 245/50-16's. That is a 25.65" tire. So, whether you will see any speedometer error with 275/40-17's will depend on which stock tires the PCM is calibrated for.

A 275/40-17 is identical in diameter to the 245/50-16, so there would be no change to the speedometer. But if you put the 275 on a car with the PCM calibrated for the 235/55-16's the speedo will read approx. 2% higher than actual speed, or it will indicate about 61mph at a true 60mph... not enough to worry about.