How does PowerPod determine the wheel size?

[ktula]

I originally posted this question on DCR. Speed sensor actually does not provide ground speed to the head unit. Instead, it sends the wheel RPM. So based on the circumference of the wheel and the current wheel RPM, the head unit calculates the ground speed.

So that makes me wonder how PowerPod determines the wheel size during the initial calibration. Does it assume it is 700×23? If my tire size is 700×33, which probably has a larger circumference than a 700×23 (2096 mm), would that affect the calibration? Wouldn't that also affect accuracy of the power data since PP must be paired with a speed sensor to function?

[Velocomp]

700 x 23 C is the default setting (circumference is 2096mm). You can adjust this in Isaac.

Calibration is not affected by wheel setting.

Power is affected by setting only if your wheel size is significantly different from 700 x 23C (for example, your using your PowerPod on a tricycle).

For most riders, the difference will be small (for example, a wheel with a 2106mm circumference, but using the default 2096 mm setting, would be "low" in watts by 2096 / 2106 = 0.5%

[ktula]

Thanks for the explanation!

[djaustin]

So when I move the PowerPod to my 406 wheeled recumbent trike, I'll have to set up the profile manually before callibration? Also I presume Crr will be higher on account of the extra wheel

[Velocomp]

Yes, you'll set up your recumbent bike on a separate profile, including wheel diameter, bike weight, CdA. Crr probably won't be much higher.