3 replies [Last post]
Anonymous's picture

Recently purchased Computrainer. Have been using Power-tap for quite a while. Does anyone have both and have used them simultaneously? Tried doing this and readings are a little skewed. Any Comments?

Anonymous's picture
John Z (not verified)
Some Ideas


1) Did you first check the PowerTap zero torque?

2) How much is the CT off? From the following as expected there is a small variation between an SRM, PT and Velodyne (Velodynes are precise). I don't have a CT, but I do have the CycleOps Electronic Plus trainer and it does read lower than a PT.

3) A quick search on the wattage forum will uncover many postings on this usbject. It does appear there is some variation in CT readings to a PM. Some is due to tire slippage and rolling resistance loss.

4) You can always check the PT against a climb."

Anonymous's picture
Steve Baccarini (not verified)
did all the warmups and zeroing etc...

Good link thanks.
Correct me If I am wrong but all erg's basically keep wattage constant to satisfy F x D = K. So if you slow down they increase the FORCE and vice -versa to keep wattage at a constant. So wouldn't it be redundant to shift gears? Shouldn't the CT compensate ( given a certain lag time) for this shift?
Ex: CT set on 300W pedaling along in 53/15 50-60 rpm to simulate climb PT reads 275... ok fine 10% difference N.P. There is probably some loss somewhere. Now shift to 39/23 actual gear(and lowest) that I would use on long climb 5% or >. PT now reads 145 watts at same RPM.Shouldn't CT increase force to keep wattage proportional?
Also download of PT info revealed
Vmax = 81 mph!
Pmax =4700 watt ( as much as a garden tractor)
Any ideas where they came from?

Anonymous's picture
John Z (not verified)

Your analysis makes sense but I don't have a CT and cannot provide much insight. I suggest data mining the wattage forum, or better yet join the list and post a question.

cycling trips