The following chart shows engine rpm at 60 mph for various combinations of final drive ratio and tire diameter. If you want to determine rpm at a speed other than 60, or for a combination of ratio and tire size not indicated here, the formula is:
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MPH x Drive Ratio x 336 = RPM
Tire Diameter
If you’d like to know your speed at a given rpm, the formula is:
RPM x Tire Diameter x 336 = MPH
Drive Ratio x 336
In both cases, “336” is simply a constant to convert the tire diameter to the linear distance the tire travels.
To determine your vehicle’s engine rpm with its present tires, simply measure the diameter with a tape. If the tires have a convex tread surface, be sure to allow for it when you measure them.
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| Engine RPM at 65 mph
Gear Ratio |
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