I got 18x7.5 rims on my car last week. People keep on telling me that my speedometer is probably off 10-12%. I figured that the car was smarter than that, but I'm not the brighest when it comes to cars. Is my speedometer off and if so, how can I fix it?
What size tires did you get? Plug the numbers in here and see the difference compared to your stock tires: http://www.gordon-glasgow.org/tirecalc.html -- Brian
if you plus-sized your tires with the larger wheels then your overall diameter should be close to the same as your stock configuration, just more wheel and less sidewall.
if its off, don't worry about it. your car will show less miles that way just remember you will be going a little faster than what your speedometer is showing.
As it stands, I believe the stock speedo reads 5mph over your actual speed. Its just sorta something you assume and keep on rolling.