to add to the confusion... if big wheels are fitted increasing the rollilng radius this would probably compensate for the <10% over-reading built into speedos, right?
if the tachometer is accurate (why would it read over?) and you know the ratios would this not give the most accurate measurement of speed???
i do have slightly larger wheels than standard and on my TDI my tacho reads a fraction under 1000rpm per 30mph in top, when i checked the manual it all added up - quotes 29.6mph/1000rpm....
oh and I got 124 on the clock but mine has K&N and modified Injectors so is clearly not 90bhp any longer....
