My Powertap G3 seems fairly unstable indoors on a KK trainer, but the ZO remains inside of their normal range of 512 ± 12.
It normally starts out 505, 2 minute later it’s 515, another 2 minutes it’s at 508. It just bounces around. It seems like after about 20 minutes it can settle down to a window of about ± 2.
I’ve never noticed this outdoors. Is this indicative of a particular problem, hopefully one that I can remedy (skewer too tight or too loose?), or does it need to go back for service?
My Powertap G3 seems fairly unstable indoors on a KK trainer, but the ZO remains inside of their normal range of 512 ± 12.
It normally starts out 505, 2 minute later it’s 515, another 2 minutes it’s at 508. It just bounces around. It seems like after about 20 minutes it can settle down to a window of about ± 2.
I’ve never noticed this outdoors. Is this indicative of a particular problem, hopefully one that I can remedy (skewer too tight or too loose?), or does it need to go back for service?
Coasting on an indoor trainer with auto-zero is deadly. With that kind of load slowing down the wheel, the zero offset is completely wrong.
Interesting point, thanks. I’ll be sure to disable it in the future. But the numbers I’m getting are from a manual calibration, when stopped, via the Garmin 800.
does that apply to other power meters such as power2max or just powertap because it is hub based
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It seems like after about 20 minutes it can settle down to a window of about ± 2.
This is why it’s best to do a manual re-cal after warmup.
Interesting point, thanks. I’ll be sure to disable it in the future. But the numbers I’m getting are from a manual calibration, when stopped, via the Garmin 800.
But is auto-zero on, and are you coasting?
Auto-zero is off and the behavior doesn’t change, I retested today.
Yes, there’s coasting, I’m not sure how I could do any of this without coasting for at least a few seconds. I have to stop the rear wheel to do a manual zero, it takes a few seconds for spin-down. Sometimes I use my rear brake to speed it up.
Auto-zero is off and the behavior doesn’t change, I retested today.
Yes, there’s coasting, I’m not sure how I could do any of this without coasting for at least a few seconds. I have to stop the rear wheel to do a manual zero, it takes a few seconds for spin-down. Sometimes I use my rear brake to speed it up.
Well, if auto-zero is off, then it’s ok. The effect I described will not kick in.
After warming up, my setup, almost identical to yours is 512 +/- 2. I find that airflow and normalizing the temperature is a big part of it. Also, tension can really screw with this number, both at the skewer (I’d guess) and the KK roller. Make them both as loose as you can without anything slipping. It doesn’t sound like anything is really wrong with your setup.
I thought about temp swings, but I keep this bike indoors, hooked up to the trainer. I plan to play with roller and skewer tension today. I’m also going to do a hanging weight / torque test, with an OIML E2 weight.
the trainer produces heat right near the hub
maybe see if a fan near the hub changes things?
Woah woah woah. I just got my powertap g3 within the last few months, but now trainer season is about to fully kick off in Georgia… So what is the proper set up/process for getting accurate power readings on the trainer? I have a cheapo sunlite mag trainer and a garmin 310 if that helps. Should I turn off auto zero? Help me out fellas!
I haven’t noticed auto zero cause any problems, but I have a big ass flywheel maybe that helps.
Anyway, I just manually zero after a warmup. You could turn off auto zero too I guess if you are worried. Or don’t coast.
Woah woah woah. I just got my powertap g3 within the last few months, but now1 trainer season is about to fully kick off in Georgia… So what is the proper set up/process for getting accurate power readings on the trainer? I have a cheapo sunlite mag trainer and a garmin 310 if that helps. Should I turn off auto zero? Help me out fellas!
I don’t think it’s temp related, even from the resistance unit. I’m getting similar results when I’m just messing with the PM, not riding it.
I’m going to start documenting it better in a spreadsheet, with ZO, hanging weight test, and time.
I just did a 1 hour workout. The fan was on me, the PT, and the Quarq. The temp in the room was stable. I’ll breakout the thermocouple next time and take a hubshell temperature before and after.
I did (3) 12’ intervals. The PMs were warmed up (5’) before the start.
Quarq / Red 22
ZO @ Start -781
ZO @ End -777
Interval #1 AP = 193w
Interval #2 AP = 197w
Interval #3 AP = 195w
PT G3 / Auto Zero = Off
ZO @ Start 513
ZO @ End 505
Interval #1 AP = 192w
Interval #2 AP = 191w
Interval #3 AP = 191w
If my math is right, and I wouldn’t mind a verification of it, a PT ZO change of 8 should yield an 23.3w shift with an average wheel speed of 20 mph (245 rpm). The Quarq ZO change of 4 should be a 1.2w diff for a cadence of 92.
I don’t understand how that can be right. The ZO calibration happened at the end of the ride, pretty close to the 3rd interval’s end. If the PT was off by 23.3w, or -8 ZO points, I’d expect the 3rd interval’s power to be really different. I’m wondering if some of the calibrations operations aren’t working properly, ie. the first one worked right (513) but the last one didn’t (505). But, I did do it more than once to confirm the 505 was repeatable.