Last updated: June 13, 2009
A common endearing (or irritating, depending on your point of view) feature of the BMW airheads is a very optimistic speedometer. Hopefully the police models (mostly RT's) had more accurate speedos, because if they clocked folks using the stock speedo, they would have written everyone speeding tickets. Joseph Dille has written some excellent instructions on recalibrating them.
What your speedometer should read at RPM in each gear. Similar to graph from "Rider's Manual US Models R65 R80 R80RT", but recreated from first principles:
MPH = (2*pi*tire_radius*RPM)/(1056*Gear_Ratio*Final_Drive_Ratio)
RPMs at 55 and 70 MPH for all Airhead ring-gear ratios can be found here.
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