This Flywheel Torque Calculator converts wheel torque to estimated flywheel torque or flywheel torque to wheel torque. Formula: flywheel torque = wheel torque ÷ drivetrain efficiency.
When Your Dyno Sheet and Your Spec Sheet Don’t Agree
A hub dyno reads wheel torque. The window sticker, the manufacturer’s spec sheet, and most tuning forums talk in flywheel (crank) torque. Those two numbers are never the same, and the gap between them is exactly what gets lost between the engine and the pavement — through the gearbox, the differential, and every bearing and shaft in between.
Two Directions, One Calculation
This calculator runs in one of two directions depending on what you already know:
- Wheel Torque to Flywheel Torque — you measured torque at the wheels (dyno run) and want to back-calculate what the engine produced at the crank.
- Flywheel Torque to Wheel Torque — you have the engine’s rated or claimed torque figure and want to know what should actually reach the wheels after drivetrain losses.
Switching modes resets the torque field to a sensible starting value for that direction (350 lb-ft / 475 Nm for wheel-side, 410 lb-ft / 560 Nm for flywheel-side), since the two numbers describe different points in the drivetrain and shouldn’t share a default.
What Drivetrain Layout and Transmission Actually Change
The calculator doesn’t measure your specific drivetrain — it applies a fixed efficiency assumption based on layout and transmission type:
- Front-wheel drive: 10% base loss
- Rear-wheel drive: 15% base loss
- All-wheel drive: 20% base loss
- Torque converter automatic adds a further 5% loss; manual or dual-clutch adds none
An AWD car with a torque converter automatic is therefore assumed to lose 25% of engine torque before it reaches the wheels, while a manual FWD car loses only 10%. That’s a wide spread, and it’s the single biggest factor driving the result — not the torque number itself.
Calculator Used Formula
Total Loss Percentage: Loss % = Drivetrain Base Loss % + Transmission Loss %
Drivetrain Efficiency: Eff = 1 − Loss %
Flywheel Torque (from Wheel Torque): Engine Torque = Wheel Torque ÷ Eff
Wheel Torque (from Flywheel Torque): Wheel Torque = Engine Torque × Eff
Torque Lost to Drivetrain: Loss Torque = Engine Torque − Wheel Torque
Loss Multiplier: Loss Multiplier = 1 ÷ Eff
Horsepower: HP = (Torque in lb-ft × RPM) ÷ 5252
Metric Horsepower: PS = HP × 1.013869
lb-ft to Nm: Nm = lb-ft × 1.355818
Nm to lb-ft: lb-ft = Nm × 0.737562
Reading the Output
The headline figure is the converted torque value — flywheel torque if you entered wheel torque, or wheel torque if you entered flywheel torque. Below it, the calculator breaks the same result down four ways: the raw torque absorbed by the drivetrain, the equivalent horsepower at both the wheel and the crank (calculated at the RPM you entered, since horsepower depends on RPM while the torque conversion itself does not), the same torque figures converted to the opposite unit system, and what the required engine torque — or resulting wheel torque — would look like if the car used a different drivetrain layout instead.
That last comparison is useful when you’re cross-shopping platforms: the same wheel torque target demands noticeably more crank torque from an AWD setup than from a FWD one, purely because more of it gets absorbed before reaching the ground.
Worked Example
350 lb-ft measured at the wheels, 4,500 RPM, rear-wheel drive, manual transmission:
- Loss % = 15% + 0% = 15%, so Eff = 0.85
- Engine Torque = 350 ÷ 0.85 = 411.76 lb-ft
- Loss Torque = 411.76 − 350 = 61.76 lb-ft (Loss Multiplier = 1.18x)
- Wheel HP = (350 × 4,500) ÷ 5,252 = 299.89 WHP; Engine HP = 352.81 BHP (357.70 PS)
- In Nm: 558.28 Nm engine, 474.54 Nm wheel, 83.74 Nm lost
- Same wheel torque on FWD would only need 388.89 lb-ft at the crank; on AWD it would need 437.50 lb-ft
Where the Estimate Stops Being Exact
The loss percentages used here are flat industry-style estimates, not a measurement of your specific car. In reality, drivetrain loss isn’t a single fixed number — it’s a curve made up of constant mechanical friction plus RPM-dependent fluid and gear resistance, which is why two cars with the same on-paper layout can dyno differently. Treat the flywheel or wheel torque result as a reasonable estimate for comparison, not a substitute for an actual chassis dyno pull.
Common Questions
Why did the torque value change when I switched modes?
The default resets because wheel-side and flywheel-side torque are different physical quantities — carrying over the same number across modes would imply zero drivetrain loss, which isn’t realistic.
Does changing the RPM change the torque conversion?
No. RPM only feeds the horsepower calculation. The torque conversion between wheel and flywheel depends solely on the drivetrain layout and transmission loss percentages.
Why does AWD require more engine torque than FWD for the same wheel number?
AWD carries a higher assumed base loss (20% vs. 10% for FWD) to account for the extra transfer case and second differential, so more crank torque is needed to deliver the same torque at the wheels.