Vehicle Speed at RPM Calculator
Calculate vehicle speed at any engine RPM from tire diameter, gear ratio and axle ratio. Results in mph and km/h for every gear.
Estimate speed from RPM and gearing.
Vehicle Speed at RPM Calculator: Tire Size Inputs
Compare two tire sizes here. Use the formulas and reference tables below for this tool's specific calculation.
How Vehicle Speed at RPM Calculator Works?
The Vehicle Speed at RPM Calculator works by dividing engine RPM by the total drive ratio to get wheel RPM and multiplying by tire circumference. The tool uses 4 steps.
Enter the tire
Type a size or diameter, for example 25 in (635 mm).
Enter the gear and axle ratios
Type the gear ratio (1.43 for 3rd gear) and axle ratio (4.10).
Enter the RPM
Type the engine speed, for example 6,000 RPM at redline.
Read the speed
The calculator returns about 76 mph (122 km/h) for that gear at that RPM.
Vehicle Speed at RPM Calculator Formula
The Vehicle Speed at RPM Calculator formula is MPH = (RPM × Tire diameter in) ÷ (Gear × Axle × 336.13).
MPH = RPM × D_in ÷ (G × A × 336.13)km/h = RPM × D_mm ÷ (G × A × 5,305.2)RPM_wheel = RPM ÷ (G × A)- RPM
- Engine speed
- D_in, D_mm
- Tire diameter
- G × A
- Total drive ratio
Worked example
A car with 25 in tires, a 4.10 axle and a 2.07 second gear reaches 6,000 RPM at 6,000 × 25 ÷ (2.07 × 4.10 × 336.13) = 52.6 mph (84.6 km/h).
Vehicle Speed at RPM Calculator Conversion Table
The Vehicle Speed at RPM Calculator conversion table lists speed at 7 engine speeds in 4 gears for a 25-inch (635 mm) tire and a 4.10 axle.
| Engine RPM | 1st (3.36) | 2nd (2.07) | 3rd (1.43) | 4th (1.00) |
|---|---|---|---|---|
| 1,500 | 8.1 mph (13 km/h) | 13.1 mph (21 km/h) | 19.0 mph (31 km/h) | 27.2 mph (44 km/h) |
| 2,000 | 10.8 mph (17 km/h) | 17.5 mph (28 km/h) | 25.4 mph (41 km/h) | 36.3 mph (58 km/h) |
| 2,500 | 13.5 mph (22 km/h) | 21.9 mph (35 km/h) | 31.7 mph (51 km/h) | 45.4 mph (73 km/h) |
| 3,000 | 16.2 mph (26 km/h) | 26.3 mph (42 km/h) | 38.1 mph (61 km/h) | 54.4 mph (88 km/h) |
| 4,000 | 21.6 mph (35 km/h) | 35.1 mph (56 km/h) | 50.7 mph (82 km/h) | 72.6 mph (117 km/h) |
| 5,000 | 27.0 mph (43 km/h) | 43.8 mph (71 km/h) | 63.4 mph (102 km/h) | 90.7 mph (146 km/h) |
| 6,000 | 32.4 mph (52 km/h) | 52.6 mph (85 km/h) | 76.1 mph (122 km/h) | 108.8 mph (175 km/h) |
What is Vehicle Speed at RPM Calculator?
A Vehicle Speed at RPM Calculator is a tool that predicts road speed at a given engine speed for a chosen gear, axle ratio and tire size. The tool is the inverse of the Engine RPM at Speed Calculator.
Racers use the tool to find top speed in each gear at redline. Truck owners use the tool to find the speed at the engine's peak torque.
The result is theoretical. Clutch slip, torque converter slip and tire growth at high speed shift the real number by 1% to 3%.
What are the uses of Vehicle Speed at RPM Calculator?
There are 4 main uses of the Vehicle Speed at RPM Calculator, including top speed per gear and drag strip gearing.
Top speed per gear
Find the speed at redline in each gear.
Drag strip gearing
Check whether the car crosses the finish line before the last shift.
Peak torque speed
Find the road speed at peak torque for towing.
Speed limiter planning
Check whether gearing allows the limiter speed in top gear.
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