Bizarre power peaks

SteilRider said:

I wonder if anyone has experienced the same problem ...

Yesterday I was riding on the trainer (Kurt) and all of a sudden, the computer went crazy giving me readings of 800+W. It lasted maybe 5 seconds and then came back down slowly to about 270, which was the correct value. It's the second time that my CPU gives me such readings.

I've never experienced this problem on the road.

Is there a known reason for this? Is there a way to fix it?

Thanks in advance!

What powermeter? - TF

Terry Ferguson said:

What powermeter? - TF

PowerTap SL.

SteilRider said:

PowerTap SL.

Check to make sure the end nuts on the axle are tight. When they're loose, you'll get all sorts of data craziness (speed/power dropouts, spikes, etc.).

To tighten the end nuts (aka, lock nuts) remove the wheel from the bike, take out the skewer then remove the cassette. Now insert a #5 Allen wrench into the non-driveside of the axle then tighten the driveside end nut with a 17mm cone wrench.

Keeping the Allen inserted, now use the same 17mm cone wrench to tighten the non-driveside end nut. Hint: you may have to think about which way to turn the wrenches to tighten. It's not intuitive if you're used to tightening hubs with two lock nuts per side.

The PowerTap SL manual says to tighten both end nuts to 12lbs-ft, but that seemed excessive to me...like I was going to strip the end nuts. So I just used gumption (went by feel).