Wheel HP ↔ Crank HP Calculator
Convert wheel horsepower to crank (and back) for your drivetrain.
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How it works
A chassis dyno measures power at the wheels (WHP), after the gearbox, driveshafts and tyres have taken their cut. “Crank” or “flywheel” HP is what the engine makes before those losses — the number manufacturers quote. This calculator converts between them using a typical drivetrain loss for your layout.
Rough losses: front- and rear-wheel-drive manuals lose ~15%, all-wheel-drive ~20–25% (more moving parts). These are estimates — real loss varies with the specific transmission, tyres and even dyno type, which is why comparing dyno numbers between different dynos is unreliable.
What matters isn’t the crank estimate — it’s a real before/after on the same dyno. That’s how we prove every DMS gain: same rollers, same day, same car.
These figures are engineering guidelines to help you plan. The reliable number always comes off the dyno — that's how every DMS build is proven.
FAQ
Is drivetrain loss really 15%?
It’s a common approximation for manual FWD/RWD. It’s not a fixed percentage — it varies with the transmission, tyres, temperature and dyno. Treat the crank figure as an estimate, not gospel.
Why do AWD cars lose more?
More components between engine and road — transfer case, extra diffs and driveshafts — each absorbing power. 20–25% is typical for AWD.
Should I trust crank figures from ads?
Be sceptical of “crank hp” claims with no dyno sheet. A real, same-dyno before/after at the wheels is far more meaningful than a calculated crank number.