I have been bugged with this little question for some time now, and no I did not find any related topics. Do you have to recalitbrate your speedometer if you increase the size of your rims?
no, all other things being the same ... it's the tire diameter, not the rim that drives speedo calibration .... if you keep the overall tire diameter the same, you can have a range of rim sizes .... tire diameter is equal to the rim diameter plus 2 times the sidewall "height" (which equals aspect ratio times section width more or less) .... so you can trade tire width, aspect ratio and rim size to get the same (or nearly so) overall tire diameter .... there are many web sources of tire size calculators on the web and quite a few tables of same ... happy surfing ....