Torque Loss Calculator takes advertised crank torque, dyno wheel torque, RPM, and gearing to return drivetrain loss percentage, power lost, and the resulting ground-force penalty.
Estimate Drivetrain Loss Between Crank and Wheel Torque with the Torque Loss Calculator
Dyno operators and tuners use the Torque Loss Calculator to see how much torque a drivetrain consumes between the crankshaft and the wheels. It compares advertised crank torque against a dyno wheel-torque reading at the same RPM, then converts that gap into a loss percentage, a horsepower figure, and a ground-force penalty.
Entering Crank Torque, Dyno Wheel Torque, and Gearing
Choose Imperial (lb-ft, HP) or Metric (Nm, kW), then enter advertised crank torque and dyno wheel torque measured at the same RPM.
Add that RPM, total gear reduction (transmission ratio times final drive), and driven tire diameter — gear reduction and tire size only affect the ground-force card, not the loss percentage itself.
Horsepower uses the standard $HP = Torque \times RPM / 5252$ relationship in Imperial mode, or the metric equivalent near $kW = Torque \times RPM / 9548.8$
How the Torque Loss Calculator Compares Crank and Wheel Torque
The core relationship: $$Loss (\%) = \frac{Crank\ Torque – Wheel\ Torque}{Crank\ Torque} \times 100$$
This is the same input-versus-delivered framing used in general mechanical torque-loss calculations for motors and machinery, applied here to a crank-versus-wheel dyno comparison.
One live mistake: pulling wheel torque from a different point on the curve than the crank figure. Torque curves aren’t flat, so comparing two different RPM points mixes curve shape into what should be a pure drivetrain-loss number.
The tool’s built-in benchmark percentages — roughly 10% for a FWD manual, 15% for a RWD manual, 18% for an automatic, 20%+ for AWD — are a widely repeated dyno-tuning rule of thumb, not a measured standard.
Real dyno reports disagree substantially: build-forum threads document FWD and RWD losses anywhere from about 7% up past 30% for nominally similar layouts, depending on tire pressure, differential condition, and dyno type, so treat these figures as a rough starting point rather than a fixed spec.
Worth knowing: drivetrain loss doesn’t necessarily scale as a fixed percentage when power goes up. Forum-documented comparisons on the same engine at different output levels suggest parasitic loss behaves more like a semi-fixed absolute amount than a strict percentage, so applying a stock car’s loss percentage to a heavily modified version of the same car tends to overstate the loss.
Crank torque must be at least 10, wheel torque at least 5 and strictly less than crank torque, RPM at least 500, gear reduction at least 1, and tire diameter above the selected unit’s minimum. Wheel torque can never validly equal or exceed crank torque — a drivetrain doesn’t add torque, so the calculator halts rather than return a negative loss.
Common Torque Loss Calculator Input Mistakes
Comparing a manufacturer’s advertised (often rounded or conservative) crank torque figure against a wheel reading from an unrelated dyno calibrated differently.
Reading the wheel-torque RPM off the rollers rather than referencing it back to the same engine RPM point used for the crank figure.
Leaving tire diameter or gear reduction at old values after a gearing or wheel/tire change — it won’t affect the loss percentage, but it will skew the ground-force thrust card.
Torque Loss Calculator Questions From Dyno Tuners
Why does my dyno number come in lower than the factory spec sheet?
Manufacturers quote power and torque at the crankshaft; a dyno measures what actually survives at the wheels after drivetrain loss, so a lower wheel figure than the sticker is expected, not a sign anything is wrong.
What’s a normal drivetrain loss percentage?
There’s no single agreed number — cited figures for similar drivetrains range from roughly 7% to over 30% depending on the source, dyno type, and the specific car’s condition.
Does the loss percentage stay the same as I add more power?
Not necessarily. Real-world comparisons suggest the absolute torque or power lost to the drivetrain stays closer to constant than the percentage does, so a modified engine’s loss percentage often comes in lower than a stock baseline would suggest.
Can wheel torque ever be higher than crank torque?
No — that would mean the drivetrain added torque, which isn’t physically possible. A result like that usually points to an underrated factory crank figure or outdated baseline data entered into the comparison.