§ How it works

Manufacturers quote power at the flywheel. A chassis dyno measures it at the tires. In between sit the clutch or torque converter, gearbox, propshaft, differential, CV joints and the tires themselves, and each takes a small cut.

P_{\text{wheel}} = P_{\text{crank}} \times (1 - L) \qquad\qquad P_{\text{crank}} = \frac{P_{\text{wheel}}}{1 - L}

where $L$ is the fractional loss (0.15 for 15 %). Note the second form divides: 180 kW at the wheels with 15 % loss is $180 / 0.85 = 212$ kW at the crank, not $180 \times 1.15 = 207$ .

Typical values

Front-wheel drive, manual: 10 to 13 %. Short path, no propshaft, no hypoid gears.
Rear-wheel drive, manual: 13 to 17 %. The hypoid ring and pinion slide as well as roll.
All-wheel drive: 18 to 25 %. Two or three differentials plus a transfer case.
Torque-converter automatics add a few points over a manual; dual-clutch boxes are close to manuals.

§ How it works

P_{\text{wheel}} = P_{\text{crank}} \times (1 - L) \qquad\qquad P_{\text{crank}} = \frac{P_{\text{wheel}}}{1 - L}

where $L$ is the fractional loss (0.15 for 15 %). Note the second form divides: 180 kW at the wheels with 15 % loss is $180 / 0.85 = 212$ kW at the crank, not $180 \times 1.15 = 207$ .

Typical values

Front-wheel drive, manual: 10 to 13 %. Short path, no propshaft, no hypoid gears.
Rear-wheel drive, manual: 13 to 17 %. The hypoid ring and pinion slide as well as roll.
All-wheel drive: 18 to 25 %. Two or three differentials plus a transfer case.
Torque-converter automatics add a few points over a manual; dual-clutch boxes are close to manuals.

Crank vs Wheel Power

Inputsdrag · tap · type

Fig. 10Power flow, flywheel to tarmac

§ How it works

Typical values

Crank vs Wheel Power

Inputsdrag · tap · type

Fig. 10Power flow, flywheel to tarmac

§ How it works

Typical values