Tire Size/RPM/Ratio Chart
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 measure. If the tires have a convex tread surface, be sure to allow for it when you measure them.
Engine RPM at 60 MPH
| Ratio | 31" Tire | 32" Tire | 33" Tire | 34" Tire | 35" Tire | 36" Tire |
| 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 | 2050 | 2000 | 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 |