I got a bullshit ticket today for doing 62km in a 50 km zone - I'm damn sure I was only doing about 55 - 58 and the cop did only give me a 58 ticket. I have aftermarket 15" rims and am wondering if that effects the speedo reading as stock on my 87 n/a is 14". I know that taxis have to have their meters adjusted depending on the wheel and tire size - could the 1" wheel size difference with stock tires give a 10 % difference in the speedo reading?

 

Wheel diameter is not important, the right tire diameter for your wheels is. What size are they?

 

It all depends on how large the stock tire diameter is. If you have rims that are 1" larger than stock then u need tires that have 1/2" less of a sidewall to be equal.

 

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