Check this website out, it has some good write up on the effects of changing tyre sizes and rim sizes.Car BibleNow, can anyone confirm to me what is the Stock Standard Tyre/Rim size for a 96 e36 318i? I am currently using 225/40/18 tyres on my ride, and if compared to a 15 inch rim, that will throw all my speed meters and distance calculations by almost 8%.