What happens if a Stages power meter isn't properly torqued?

[jspaceman]

I recently bought a Stages DA9000 power meter from a LBS. They installed it for me. The next day I went to do a ride and about 10km into it I noticed my pedaling started to feel wobbly. I stopped and looked at the crank. The Stages crank arm was coming loose. It appears as though the bike shop didn't torque the pinch bolts enough and it came loose as I was riding. I tightened the bolts down with a hex key I had in my saddle bag and continued the ride. I didn't torque them too hard, so it's likely they are still under-torqued; but I torqued them enough so that they stayed on for the rest of the ride.

I am going to buy a torque wrench and reinstall the power meter myself later this week.

Last night I did a ride on my Wahoo Kickr with the Stages on the bike. The Trainer Road app on my computer displayed the wattage reported by the Kickr, and the Garmin Edge 500 on my bike displayed the wattage reported by the Stages. I noticed that the Stages was under-reporting my wattage by around 35-40W. Is it normal for the Stages to under-report wattage if it isn't properly torqued to the crank?

[spdntrxi]

Read up on the kickr.. Many think the kickr is the issue reading higher and I tend to agree that it does read higher .. The kickr that is

I do see 20w sometimes.. Most of the time less

[aaric]

My kickr will read high if I calibrate it within the first 15m or so of use. Once I started doing the spindowns at the end of sessions, it has been much more consistent with my SRM numbers.

[TrevorDeRuise]

Just about all power meters vary small amounts in accuracy. I would imagine this is exactly what you're seeing here, rather than an issue with the torque of your crank. The most crucial part of training is not necessarily having the most accurate power numbers, but rather the most consistent.

Wahoo recently made it possible to control the Kickr via an external power meter. Since it seems as though your Stages and Kickr are putting out slightly different readings, by trying this new release with the Kickr you can make sure your power readings are identical while out on the road and inside on the trainer. Check out this thread: http://forum.slowtwitch.com/forum/Slowt ... _P5396505/

-Trevor from TrainerRoad

[droid1973]

I don't believe that torque spec will affect the stages crank

[jspaceman]

I found this at the Stages web site:

We calibrate the Stages Power meter at 12-14 Nm for Shimano cranks; 48-54 Nm for SRAM BB30 and GXP; 40 Nm for Cannondale; 45-55 Nm for FSA MegaExo; and 38-41 Nm for FSA BB30/BB386, thus it is important to install your Stages meter at or near these same torque values for best possible operation. We cannot recommend installing the Stages Power meter without a torque wrench. If this is you’re only option, please visit your local bicycle dealer.

I bought a torque wrench and reinstalled the Stages this evening. Torqued the pinch bolts to 13Nm.

Just as a quick test I hooked the bike up to my Kickr and connected the Kickr to the Wahoo Fitness app on my phone via Bluetooth. I connected the Stages to my Garmin Edge 500 via ANT+. I had the Kickr in erg mode and spun it at 200W. The Wahoo app showed me doing ~200W, the Stages reported anywhere from 185W to 205W. I realise they're not going to be in exact agreement. And I should add that I did a spindown test on the Kickr only after a few minutes riding, so perhaps it hadn't had time to fully warm up. It seems when I spin fast, say above 100rpm, the Kickr and Stages wattages are in closer agreement than when I spin slower.

I should note that I also have a Powertap hub built into a wheel on my other bike. I might put that on the bike with the Stages and go for an outdoor ride sometime to see how closely the two power meters agree.

[mullarted]

I have a Kickr and a Stages power meter.

I'm running a beta version of TrainerRoad that (very simply) uses the power reading from the Stages to drive the resistance on the Kickr. This is to remove the discrepancy that people are seeing betwwn two power meters.

What i've found by doing this is that my power is a lot more 'jumpy'. I suspect the heavy fly wheel on the Kickr has quite a smothing effect on power. I was able to very accutately hit and maintain power numbers just using the Kickr.

When I introduced the Stages in to the mix I think I see what you do. Power moving in a range around, say 200, from 190 to 210.

[showdown]

One thing that helps (a lot with Stages) is setting the power display on your head unit to 3 second or 5 second average. It helps smooth out those little jumps and dips that come with a one-sided measuring device. The kickr is much smoother though and much more pleasant when doing longer steady intervals.