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Part 2

Provided By: Patrick Kelley

This is the actual ratio determined by number of revolutions a tire turns in one mile compared to the engine rpm at 60 mph. The tire diameter is the loaded diameter measured from the ground to the axle center times two. This is usually different than the diameter given by the manufacturer and varies with vehicle weight and tire pressure. In my experience, the loaded dia can be 1 to 2 inches smaller than the unloaded dia.

Obviously, some of these are theoretical gear ratios but should provide some guidance is selecting the proper combination of gears and tires for the desired 60mph engine speed.

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Ratio Factors for a given tire size

RF-1 2250 RPM @ 60 MPH Tire Dia Gear Ratio 22.0 2.45 22.5 2.51 23.0 2.57 23.5 2.62 24.0 2.68 24.5 2.73 25.0 2.79 25.5 2.84 26.0 2.90 26.5 2.96 27.0 3.01 27.5 3.07 28.0 3.12 28.5 3.18
RF-2 2500 RPM @ 60 MPH Tire Dia Gear Ratio 22.0 2.73 22.5 2.79 23.0 2.85 23.5 2.91 24.0 2.98 24.5 3.04 25.0 3.10 25.5 3.16 26.0 3.22 26.5 3.28 27.0 3.35 27.5 3.41 28.0 3.47 28.5 3.53
RF-3 2750 RPM @ 60 MPH Tire Dia Gear Ratio 22.0 3.00 22.5 3.07 23.0 3.14 23.5 3.20 24.0 3.27 24.5 3.34 25.0 3.41 25.5 3.48 26.0 3.55 26.5 3.61 27.0 3.68 27.5 3.75 28.0 3.82 28.5 3.89
RF-4 3000 RPM @ 60 MPH Tire Dia Gear Ratio 22.0 3.27 22.5 3.35 23.0 3.42 23.5 3.50 24.0 3.57 24.5 3.64 25.0 3.72 25.5 3.79 26.0 3.87 26.5 3.94 27.0 4.02 27.5 4.09 28.0 4.17 28.5 4.24
RF-5 3250 RPM @ 60 MPH Tire Dia Gear Ratio 22.0 3.55 22.5 3.63 23.0 3.71 23.5 3.79 24.0 3.87 24.5 3.95 25.0 4.03 25.5 4.11 26.0 4.19 26.5 4.27 27.0 4.35 27.5 4.43 28.0 4.51 28.5 4.59
RF-6 3500 RPM @ 60 MPH Tire Dia Gear Ratio 22.0 3.82 22.5 3.90 23.0 3.99 23.5 4.08 24.0 4.17 24.5 4.25 25.0 4.34 25.5 4.43 26.0 4.51 26.5 4.60 27.0 4.69 27.5 4.77 28.0 4.86 28.5 4.95