New Bike, Now TR Power 2-5% Lower Than PM

I got a new bike on Friday and have noticed that TrainerRoad power is 2-5% lower than my power meter. However, when doing a free ride in Zwift, its power matches my PM nearly identically.

Old bike had a Shimano drive train. New bike is Sram AXS. I moved my Assioma DUOs from my old bike to my new bike and “set” them by doing a bunch of sprints. I have a Kickr Core 2018 and changed the free hub and installed the Sram cassette without issues. I have performed numerous spin downs on the Kickr and manual calibrations on the Assiomas.

When performing structured workouts I load Zwift on a Mac Book Pro and connect it to the Kickr via Bluetooth. I do not let Zwift control the trainer. I then load TR on the same laptop and connect it to the Kickr via an Ant+ dongle. Separately I record power from the Assiomas on a Garmin Edge 830. (Yes, I know I can use Power Match but I separately record power from the different sources this way to detect these exact issues. I may use Power Match as a last resort if we can’t figure this out but I want to troubleshoot first.)

Here is this morning’s attempt at some VO2 intervals. Purple is TR/Zwift, blue is the Assiomas. The Assiomas were consistently 2-4% higher than TR. (Again, I know this is within the +/- 1-2% error per device).

However, and here’s the kicker (no pun intended), when I bailed on the structured workout and free rode in Zwift (closed TR), the power from the Kickr and Assiomas agreed within 0.3%, which is what I was used to seeing on the previous bike.

Other than the different drive trains and cassettes, the old bike had 170mm cranks and new bike has 172.5mm. Neither of these should make a difference, though, since TR gets is power data directly from the trainer (or Assiomas if setup that way). I will email with this but would like to know any thoughts from the community. Thanks!

Check in the Assioma app that it’s using the Unified left channel to broadcast rather than broadcasting from each pedal individually.

If I’m remembering correctly the Assiomas behave differently depending on connection type and the difference you are seeing might be down to l/r leg imbalance.

1 Like

Also switch off the Kickr’s Erg Mode Power Smoothing

@guyc the Kickr’s power smoothing is off.

@JulianM I will double check but the RPE matched the power reported by the Assiomas, not the Kickr/TR. Plus the Assiomas match the Kickr when only Zwift is involved, not TR.

1 Like

You’re getting the right advice here, but feel free to reach out to the team in the future as more questions about devices and discrepancies arise. Troubleshooting can also very much depend upon the make and models of your devices, device software versions, any firmware updates that are needed, etc. Support will have the best recommendation based upon what you’re working with!

From the ‘Welcome to the TrainerRoad Forum’ Page:
Have a question about the app, your training plan, or device? Reach out to instead of posting here. Our support team has the best visibility and insight into your devices, workouts and adaptations, and will help get you the most efficient and effective answer to your question.

If I understand you correctly, when you do these power comparisons, you are always recording the Assiomas using the Garming 830, right? I assume that you changed the crank length setting for the Assiomas in the Garmin when you changed bikes.
You’ll want to make sure that whatever device is connecting to the Assiomas has the correct crank length configured. As I understand it, the value set in the Assioma app is only used as a default if the device connecting to the pedals doesn’t set a crank length.

1 Like

Yes, I did update the crank length in the Edge as well as the Assioma app. Thanks.

I’m really at a loss as to why the Assiomas and Kickr agree when Zwift is the only app involved, but TR is 2-4% lower, which translates to 2-4% harder at the pedals, which is noticeable.

TR Support recommended swapping the Bluetooth and Ant+ connections to see if the discrepancy follows the network protocol. I’ll do that as soon as I get a chance, and try just TR by itself. More later this week. Keep the ideas coming, please!

Are you using ERG mode when TR is controlling the trainer? I think Zwift will be using slope mode (at least not ERG) when just riding. I would hope that power reporting accuracy would be the same for the kickr in both modes, but this is a difference. I don’t think this part has changed from your before/after tests, and if not this wouldn’t explain your discrepancies.
I could see how the kicker ERG mode power smoothing could cause a difference here, but from what you have described nothing has changed from your before/after tests other than the bike. I don’t have an explanation of why power smoothing would affect 1 bike and not the other, but you certainly want it off if you are comparing power. (I guess gearing could have an effect, but I would expect large gearing changes to be required to have a significant effect.)

I agree that swapping protocols is worth a try, and I think with TR alone trying both ERG and slope mode as well, this would help tell if the trainer resistance mode is a factor or not.

1 Like