tristatez28lt1

im gonna put 18 inch wheels with 275/35ZR18 tires on my car (96 Z28 with stock salad shooters). Does my speedometer read wrong when I have them put on. I have a HPP III lying around if it is going to read wrong I can change it with the HPP II right? just a quick question.

Deep Blue

If the overall wheel/tire diameter changes significantly, you will actually be traveling at a different speed than the speedometer reads. If you do a search or go to Discount Tire's website, there are some calculators that can give you an idea.

Zymosis

iTrader: (7)

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

02_Phase2_ZL1

The overall rolling diameter of P235/55R16, P245/50R16, P275/40R17 and P275/35R18 are all the same so you shouldn't have any problem at all. You speedometer and odometer should all be fine.

jayredSS

well my brothers speedometer is off by about 7 we are runnin 17x11. but the hypertech power programmer can fix that. thats if you want to spend 300 dollars to fix it.

TooSlow02

I have 275/35R18 tires, and my speedo calibration is fine.

joblo1978

iTrader: (14)

You can search for a wheel and tire calculator and it will tell you the differences but they're pretty small and not much to worry about with the size you're going. The size your going to is almost identical to stock. If you get tuning in the future I would go ahead and recalibrate anyway though.

Xsta Z 28

iTrader: (2)

Wheel size has absolutely no affect on the speedo . . . its the overall diamater of the tire.

So in the stickys are some tire calculators, to help in your tire choice, but as JD said all those tires are the same OD, so there should be no change