Wheel Torque Change Calculator
Model how gearing and tire radius change torque and force at the wheels. Compare axle torque and ground force for two tire sizes.
Model gearing and tire-radius effects.
Wheel Torque Change Calculator: Tire Size Inputs
Compare two tire sizes here. Use the formulas and reference tables below for this tool's specific calculation.
How Wheel Torque Change Calculator Works?
The Wheel Torque Change Calculator works by multiplying engine torque through the gear, axle and efficiency factors, then dividing by tire radius to get force at the road. The tool uses 4 steps.
Enter engine torque
Type peak torque, for example 400 N·m (295 lb·ft).
Enter ratios and efficiency
Type gear ratio (4.70), axle ratio (3.73) and drivetrain efficiency (85%).
Enter 2 tire sizes
Type the stock and new tire diameters.
Compare results
The calculator returns axle torque, ground force for each tire and the percent change.
Wheel Torque Change Calculator Formula
The Wheel Torque Change Calculator formula is T_axle = T_engine × G × A × η, and ground force is F = T_axle ÷ r.
T_axle = T_eng × G × A × ηF = T_axle ÷ rΔF% = (r₁ ÷ r₂ − 1) × 100- T_eng
- Engine torque (N·m)
- η
- Drivetrain efficiency (0.80–0.90)
- r
- Tire radius (m)
Worked example
400 N·m (295 lb·ft) × 4.70 × 3.73 × 0.85 gives 5,961 N·m (4,397 lb·ft) of axle torque. With a 31.6 in tire (0.401 m radius), ground force is 14,852 N. With a 35 in tire (0.445 m radius), ground force drops to 13,411 N (3,015 lbf), a 9.7% loss.
Wheel Torque Change Calculator Conversion Table
The Wheel Torque Change Calculator conversion table shows ground force for 6 tire diameters with identical engine and gearing inputs.
| Tire diameter | Radius | Axle torque | Ground force | Change vs 31.6 in |
|---|---|---|---|---|
| 28 in (711 mm) | 356 mm | 5,961 N·m | 16,762 N (3,768 lbf) | +12.9% |
| 30 in (762 mm) | 381 mm | 5,961 N·m | 15,644 N (3,517 lbf) | +5.3% |
| 31.6 in (803 mm) | 401 mm | 5,961 N·m | 14,852 N (3,339 lbf) | +0.0% |
| 33 in (838 mm) | 419 mm | 5,961 N·m | 14,222 N (3,197 lbf) | -4.2% |
| 35 in (889 mm) | 444 mm | 5,961 N·m | 13,410 N (3,015 lbf) | -9.7% |
| 37 in (940 mm) | 470 mm | 5,961 N·m | 12,685 N (2,852 lbf) | -14.6% |
What is Wheel Torque Change Calculator?
A Wheel Torque Change Calculator is a tool that models how tire radius and gearing change the force a vehicle puts on the road. Axle torque stays the same when only the tire changes. Ground force falls as the radius grows.
Force at the road drives acceleration, hill climbing and towing ability. A 10% taller tire cuts ground force by about 9%.
The model uses static radius and steady efficiency. The model gives a fair comparison between setups, not an exact dyno figure.
What are the uses of Wheel Torque Change Calculator?
There are 4 main uses of the Wheel Torque Change Calculator, including towing ability checks and regear justification.
Towing ability checks
Measure lost pulling force after an upsize.
Regear justification
Show how much force a new axle ratio restores.
Crawl force
Compare off-road crawl force in low range.
Engine tuning targets
Set a torque goal that offsets a tire change.