What is the cheapest thing on the market to tell the computer that my car now has 18 inch wheels instead of 16?



Thanks

 

The computer does not care how high your wheel is, it uses the overall tire height to calibrate the speedo. As long as your overall tire hight is 26 inches or around that don't give it much thought, otherwise madwolf or pcmforless are your better options.

 

I know the cheapest way on my Mustangs is changing the vss gear. Can you do that on a Camaro?

But sss is right. If you compensate for the extra wheel by getting a shorter sidewall, you don't have to change anything. You may be 1 or 2 off if that is acceptable to you.

 

If you just want to know how fast you are going, simply get on the highway and drive for at least 10 miles while paying attention to the mile markers and noting your odometer readings. Lets say your odometer says you went 11 miles when the mile markers say you went 10. Then you know your odometer is 10% slow, meaning your speedometer is 10% slow as well.

 

My thing is i'm selling the car soon, if i was keeping it I would not worry one bit. I'm not sure how significant the difference from the 16 to the 18 is. If by some chance its changed a few mph, then mileage will be off quite a bit after a while too. I haven't drove the car much with the 18s on soo that difference is minimal

 

What size tires did your car have from the factory. There was a 235/55-16 "base" tire (26.18" diameter) on the Formula, and an optional 245/50-16 with the Z-rated tire option (25.65" diameter).

What size tires do you have on your 18" wheel?

Its very likely that there is no more than a 2 to 4% error on the speedo/odometer, and possible that there is no error as all. But no one can tell you the correct answer until you provide your original factory tire size and the tire size you have now.