Performance Converter: Translate watts into Crr and CwA/CdA coefficients

Manufacturers and test reports often state losses in watts at 40 km/h or 45 km/h. To make those numbers usable for your own race simulations, they need to be converted into speed-independent values.

Watts without the corresponding speed are meaningless. Our converters isolate the physical constants — the rolling resistance coefficient Crr and the aero drag term CwA (CdA). This makes equipment comparisons objective and transferable to any pace.

With those values, you can calculate the resulting speed (or the required watts) in the Bike Calculator: Open Bike Calculator

Aero converter (CwA)

Converts aero watts from wind-tunnel tests or field tests into a $C_dA$ value. Because aerodynamic power scales with the cube of speed ($v^3$), this calculator is essential for determining what the savings are worth at your real race pace (e.g., 35 km/h instead of the 45 km/h test speed).

Rolling resistance converter (Crr)

Tire manufacturers often publish watt losses at a standard load. This converter derives the rolling resistance coefficient ($C_{rr}$) from that data, so you can calculate how much a tire change really saves at your actual system weight and speed.

Physical modeling & data transfer

Reducing complex measurement data to the base coefficients CwA and Crr is the foundation for a valid performance prediction. While plain watt figures are only a snapshot under specific test conditions, these coefficients describe the speed-independent physical “DNA” of your setup.

Only this mathematical separation makes your setup transferable to any course and environmental conditions. That’s how you create a precise digital twin of your real-world performance.

FAQ for the coefficient calculator

Power claims in watts (e.g., “saves 10 watts”) always depend on speed. To use those numbers for your personal race simulation, you need to convert them into speed-independent coefficients like aerodynamic drag (CdA) or rolling resistance (Crr). Only then can you quantify what the savings are truly worth at your specific race pace.

If you compare two setups (e.g., an aero helmet vs. a standard helmet) and you know the watt difference at a constant speed, this calculator gives you the change in your CdA value. You can then plug that value straight into our pacing simulator to estimate the time savings on your target course.

Aerodynamic drag increases with the square of speed, which is why the required power increases cubically. Rolling resistance, on the other hand, causes a power loss that grows linearly with speed. The calculator accounts for these physical differences so the conversion stays accurate at any speed.

You’ll need the power (in watts), the speed at which that value was measured, your system weight, and ideally air density (temperature/altitude). The more accurate these inputs are, the more precise the resulting CdA or Crr value will be.