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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:
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 60 mph
tire
size/
31"
tire
32"
tire
33" tire
34" tire
35"
tire
36" tire
ratio
3.08
2000
1950
1875
1825
1775
1725
3.23
2100
2025
1975
1900
1850
1800
3.31
2150
2075
2025
1975
1900
1850
3.42
2200
2150
2100
2025
1950
1900
3.54
2300
2225
2175
2000
2050
1975
3.78
2425
2375
2300
2200
2150
2100
3.90
2550
2450
2375
2300
2250
2175
4.10
2650
2575
2500
2425
2350
2300
4.27
2775
2700
2600
2525
2450
2400
4.56
2950
2875
2775
2700
2625
2550
4.88
3175
3075
2975
2900
2800
2750
5.12
3325
3225
3125
3050
2950
2875
5.38
3500
3400
3300
3200
3100
3025
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