VW Beetles
One of the more usefull calculations when working on beetle modifications is the gear ratio calculation.
GEAR RATIO FORMULAE
MPH= (RPM x Tyre Diameter (in inches)) / (Drive Ratio x 336)
where Drive Ratio = (Ring & Pinion ratio) x (Gear Ratio)
For example, with a tyre diameter of 24ins, a final drive ratio of 3.88 and a top gear of 0.82, the road speed at 4,OOOrpm would be:
MPH = (5000 x 25) / (0.89 x 4.125 x 336)
= 125.000 / 1233.54 = 89.8mph
RPM (Using the data from the previous example, at 70mph:) = (MPH x Drive Ratio x 336 ) / Tyre Diameter (in inches)
RPM = (70 x 0.82 x 3.88 x 336) / 24 = 86.3478 / 24= 3117.9rpm