Let:
S: speed (MPH)
D1: primary drive ratio (clutch wheel ÷ motor sprocket, etc.)
D2: secondary drive ratio (rear sprocket ÷ transmission sprocket, etc.)
G: individual transmission ratio (2.50, etc.), direct drive high gear = 1.00
T: tire diameter (inches)
R: engine speed (revolutions per minute)
S = (T × R × .002975) ÷ (D1 × D2 × G)
R = (S × D1 × D2 × G) ÷ (T × .002975)
D1 = (R × T × .002975) ÷ (S × D2 × G)
D2 = (R × T × .002975) ÷ (S × D1 × G)