Stages L sided PM vs KickrCore vs Powertap Hub

Dear all,

I’m having an issue with the outdoor crank to measure power. I’ve read lots on here but don’t seem to have found a solution so I’m hoping for a miracle as opposed to wasting £300 on worthless power readings from Stages. Basically it seems to calibrate fine with acceptable number 917. Garmin picks up same. Then I go out cycling and push something like 240 watts at threshold for 25 mins For a whereas on the Kickr and Powertap hub in the past that would be closer to 300. Is it just the reality of the accuracy issues inherent in these things? It’s ultegra 8000 gen 3. If it is I’ll flog it online. I’m hoping someone has some methods to try and fix the problem. Thanks in advance.

Are you actually comparing power data with 2 meters active at the same time (via 2 recording devices live or after the fact via analysis tools), or just going by feel and perceived exertion?

Haven’t tried two at the same time as they are on separate bikes. But RPE is the same for much lower readings and analysis tools Eg TR show that to be true. Love TrainerRoad by the way. Thanks for improving my cycling.

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I’ve found the Powertap hubs tend to drift over time due to the torque tube failing and you need to keep an eye on the calibration number. I know they operate in a particular range, but I can’t remember what that is.
If possible, I would run both on the same bike, recording to two different head units to see how you get on.

Thanks for the reply. I’m thinking I’m going to have to have the stages run at the same time as the Kickr Core and compare on two different units - the Garmin edge 500 and trainer road? Hopefully that will show up the problem once and for all. It’s frustrating to see such FTP improvements only to go outside last Saturday PB a 10mile TT 24mins on a road bike and record average 239 watts at threshold and 9/10 RPE. Seems way off.

I am very interested in this as I have had a similar experience with my stages reading consistently lower than my powertap.

Yes. You have to do an actual recording on both in order to properly compare. However, eyeballing can give you a feel for how close, I would guess within 10watts. But the recording and file analysis will be best.

I’ll give it a go and report back.

sounds good. there are various tools to compare .fit files as well. I believe zwiftpower has a free one, golden cheetah, and dcrainmaker has one for a fee.

I replied with this below in a different tread but I thought its also relevant here. The stages L and my Kickr Core is quite off ( ~10% on avg). See the comparisons below.

Andrews + 1

Part of Holt Hill + 1

Part of Juneau - 1

I’m still using the Kickr Core power reading to keep consistency until my next ramp test where I’ll be using stages L instead with powermatch. Yes, I’ve done spindowns and zero offsets on both devices.

I think part of this might be due to the fact that I’m right leg dominant. If i’m really focusing on keeping a steady cadence and even power, the core and the stages seems to line up within 3% when I use the core in standard or resistance mode.

It could also be your right leg is a lot stronger than the left.

I know a lot depends on the course, how slippery you are and general conditions, but unless you had a tailwind for 10 miles, I would be surprised if you could average only 239 watts for a 24 min time, bearing in mind you’re on a road bike.

Thanks for the info. I am going to record a Zwift TTT tonight using both devices, the stages and Kickr. Hope it works and I find the problem with the stages crank. If it’s a left leg problem that’ll be great as hopefully lead to a new set of possible improvements.

Taking the previous post into account 10% would be around 264 watts. Does that seem more plausible?

60 watts is a big difference! I could see ~7 watts drivetrain efficieny lost from the crank to the rear hub (although that could be a lot more if there are absurd things like bad bearings or rusty chains). What’s the biggest L/R balance somebody might have? 5%? Still, that would be 15W. So maybe ~20W between the crank and the rear hub could be justified.

Not 60W, though. That’s a lot.

It’s possible but it’s hard to say for sure. I think your Zwift session will answer a lot and I’m looking forward to hearing the results. I’m sure you will, but just make sure everything is calibrated before hand. Also note, that the Zwift fit file won’t include your warm up in the start pen, so it might be worth hitting the lap button on the Garmin when the race starts.

Results are in for the test tonight. The TTT averaged 205 watts on the stages crank. Using the Kickr was 243 watts. That’s too much of a difference to be useable for me. Any ideas going forward? I did a quick TR workout afterwards and again it was lower - it gets worse the higher the power increases but it seems to overestimate when accelerate and then drops significantly below the ERG target coming from the Kickr driven by TR.

Is it still under warranty? If so, then it might be worth giving Stages a shout.

I’ve raised a support ticket so we will see what they do.Screen Shot 2020-05-21 at 21.44.29 Screen Shot 2020-05-21 at 21.43.18

What is more likely to be accurate - a Stages or a Kickr?

It seems like the Kickr is the preferred power meter here because it has the higher number. :slight_smile:

FWIW, I just got a Stages and couldn’t reproduce the same power outside. One thing I’ve found is that the Stages works better calibrated ten minutes into my ride after it has equalized with the outdoor temperature.

I did tests on Stages vs. my Tacx Vortex and they came up pretty close after warming up both for 10-15 minutes and then calibrating.

Yeah it could be that the Kickr has just been over-estimating power. Unfortunately I don’t have a way to compare the stages to the powertap because its ultegra 11 vs campag 10. That would be the next line of inquiry. Its just so frustrating to have such a large difference but I’ve just read up on the power match feature so I may try that tomorrow as well. On Strava I am hitting KOMs at 200 watts with threshold heartrate. That’s definitely not right as there are some quality riders who have ridden the segments.