powertap virtual cadence problems

[iliveonnitro]

I was stopped at a red light with one foot on the ground, and the other clipped in with a little force on the pedal. I scrolled to the cadence section on the PT CPU and it was reading 20-40. hmmm...

I also sometimes notice that my cadence will be high while riding. I've been riding for awhile and know what each cadence zone is, but it really doesn't seem like I'm doing 105 cadence while riding at 15mph at 150 watts. Sometimes it will be 110 when it should be closer to 95-100.

This is only occasionally, but it will happen during every ride. Should I be worried about this? Will it have an effect on its accuracy?

 

[Alex Simmons]

the cadence numbers might be a little screwy but it won't affect the power readings

 

[iliveonnitro]

the cadence numbers might be a little screwy but it won't affect the power readings

Good to know, thanks. How does the PT figure out revolutions by the hub? Eg, power = force * revolution, but how does it figure out the revolution part of it?

 

[RChung]

How does the PT figure out revolutions by the hub? Eg, power = force * revolution, but how does it figure out the revolution part of it?

It measures both torque (with strain gages) and angular velocity (with a small embedded magnet) at the rear hub. It doesn't need crank torque or pedal cadence at all in order to calculate power.

 

[iliveonnitro]

It measures ... angular velocity (with a small embedded magnet)

That's what I was looking for. Thanks.