Problems with torque on Powertap... Help please!

I was planning on doing a 2x20' 100% FTP workout today on the trainer, so I got on, zeroed the torque at the start (did it a couple times in a span of 1 minute - pedal 5 seconds, get off and zero torque, pedal again, get off, etc.) and then proceeded with warmup and workout.

Did both 1st and 2nd 20' intervals 3-4W over FTP and was feeling great (aka not a struggle but still deeper, slightly faster breathing). So I decided to do a 3rd 20' interval. At the end, I was feeling strong so I shifted two gears higher for the last 2-3 minutes and brought the average power of the interval to 8W over FTP.

Did a 10 minute cool down, got off the bike and then decided to check torque...and lo and behold holding down to display torque, I see a "4" while off the bike. So I zeroed it.

Then I got back on and did some spinning and then back to same cadence/gearing of intervals and I was getting wattage numbers about 10W lower than FTP.

So I got off, zeroed torque again, and then got back on, and now at same cadence/gearing, I was getting normal wattage numbers (~FTP)...like the workout. I got off the bike again, and then the torque display showed "4". So I zeroed it again.

Then I got on again, did the same cadence/gearing and was producing workout FTP numbers. I then got back off and zeroed torque (which was displaying 0) and did this a couple more times and each time, I was zeroing a torque reading that already read 0...but each time, the power numbers were back to normal like the workout power numbers...

Is there something wrong with my Powertap??? I looked at my file afterwards and when I "coasted" on the trainer (the few seconds the wattage read before the wheel came to a stop), every time my watts were 0, I had 0 hub torque and crank torque as well...huh? Can someone help me? Thanks.

 

This from the PowerTap manual on suspected torque issues....


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The wheel needs to be moving when zero-ing torque ie you need to be coasting but no pressure on the pedals.

 

Are you sure about that I've always zeroed my PT before each ride before I move off (not moving), but with the transmisssion icon showing

 

Pretty sure that's how the manual says to do it.
It also makes the most sense - on the very rare occasions my torque was off, it would show 0w at rest but some low number when coasting.
I got in the habit of doing it the same way every ride - ride for a few minutes until temp is stable, then coast and zero torque. Do the same with my SRM offset (although the SRM is more sensitive to temp variation.)

 

Except apparently the Saris phone reps have been contradicting the manual lately. I'll see if I can find the recent post, but I think it was not to zero while coasting; but rather to do it while not on the bike with the wheel turning (why this would matter I don't know). Also they said to hold the button down for 10 seconds, not just until it goes to zero.

I have also found it helpful to ride a bit first before zeroing.

TF

 

In my case, when I'm coasting the watts will read 0 like they should but when I get off and hold down "select" to get to the torque display, it displayed "4" or sometimes some other number...what gives?

 

Does the torque also read 4 while coasting? - TF

 

I'm not sure because I did this while my bike was on the trainer...there is hardly time for the wheel to "coast" since the flywheel brings the wheel to a halt pretty soon after you stop pedaling. I didn't look at the torque while it was "coasting" down...I only looked at the torque, which displayed "4" after the wheel had come to a halt...