Is my powertap goosed again?

Jay_Pea

It's been back from Paligap around 250km and the calibration seems low to me, does anyone know what the normal range is?

I got it back and it calibrated to 506 which matches the paperwork that came with it but it's been decreasing through today. I've also noticed that the torque readings flicker when the bike is stood still and the cranks are level. Is this normal? How much does it have to drift before Paligap would consider it faulty?

Does anyone know how I stand returning it to the place I bought it from after it's been for a warranty repair? I'm assuming I'd be ok given I have maintained it in accordance with the manufacturers instructions.

Cheers for looking

John

neeb

It's probably fine. I have two G3 powertaps, one calibrates between 511 and 514, the other between 496 and 500, but as far as I can tell they both read the same. The point of the calibration is to compensate for the individual behaviour of the particular unit as well as how this is affected by temperature etc. Also if it's just been serviced the strain gauges might be bedding in so to speak, but the calibration is there to compensate for things like that.

Do the readings seem normal on the road?

dzp1

500-525 is the acceptable range according to Saris

Try doing a weight test as described here: if you get a reasonable torque number, your PT is ok. They are usually between -1% and -2% out in y experience.

http://www.cyclepowermeters.com/powerta ... k-76-c.asp

Just make sure you get the maximum torque by trying several pedal angles.

neeb

dzp1 wrote:

500-525 is the acceptable range according to Saris

Try doing a weight test as described here: if you get a reasonable torque number, your PT is ok. They are usually between -1% and -2% out in y experience.

http://www.cyclepowermeters.com/powerta ... k-76-c.asp

Just make sure you get the maximum torque by trying several pedal angles.

I did this with mine (the one that was calibrating low), and got numbers within spec. I'd previously asked Saris if the calibration numbers were a problem and they said that the acceptable range was 512 +/- 12 "or a little bit lower..". Sounds vague I know, but I can at least confirm that it is possible to have a calibration number consistently slightly under 500 and for the power meter to be OK, so the number doesn't really tell you much by itself unless it is way out of range. I've heard that when the torque tube goes you get silly calibration numbers, like 100 or 700 or whatever.

Jay_Pea

Wow! Thanks for all the responses, didn't expect that!

@Neeb - original didn't work long enough for me to figure out if it ferels right on the road and I haven't dared put this one on the turbo incase I knack it again. Do turbos cause hub failures? It seems consistent and feels right relative to my post winter training FTP.

@dzp1 - Cheers so it looks like I'm still within acceptable parameters, if I find it strays too far outside I'll have to start hanging things off pedals

@neeb (again) - I've never found out exactly what the calibration number actually means, I'm assuming that it's some sort of correction factor the hub applies at calibration but that's just a guess, like you say fairly meaningless on its own. When the tube went last time it was calibrating to 235 and not recording any power data.

Thanks again

neeb

No particular reason why turbos should cause problems - the PT shouldn't really be able to tell the difference from being on the road. I use mine all winter on the turbo.