Sentence:  These are MPH for Car speed RPM for Engine crankshaft speed R for Rear axle gear ratio W for Tire size Tire size can be <WSD>determined</WSD> in several ways but the one that is the easiest and as accurate as any is by measuring the effective radius of a wheel and tire assembly . 
Meaning of the word marked with <WSD> tags:  establish after a calculation, investigation, experiment, survey, or study