I’m new and have searched the forums. I see a lot of discussion about calibrating power meters. I have a Tacx Neo. I’m just beginning training and did an FTP test that gave me 170 watts. I’ve since added a Stages PM and when I compare wattage between the the Stages is consistently 20ish watts lower than the Neo.
I’ve calibrated the Stages, but the Tacx Utility app won’t seem to prompt mt to calibrate the Neo. It connects and reports power but won’t prompt me to calibrate it. I’ve read you can’t calibrate the Neo, though Tacx has a blog entry about doing so on direct drive units. That may not apply to Tacx. I don’t know.
So, which should I trust? When doing my workouts it currently picks up the Stages, and it’s not very challenging.
It’s a NEO v1 and a left sided Stages. The variance seems to be pretty constant. One thing I noticed when running the app with the Stages PM is that on a couple of occasions the power output seemed to spike and it was difficult to bring the power into a reasonable range.
This morning I did a workout that included intervals that were supposed to be about 144 watts. It asked me to get out of the saddle and spin for a while at 60is RPM. I basically couldn’t do it without spinning out. It seemed like the stages was just really high and so even when I was supposed to be working hard it was easy. I’d love for that to be the case but I don’t believe it.
Poking around I suspect it’s a variety of issues popping up. Natural accuracy differences plus drive train losses.
Since I’m doing some training outdoors, maybe the thing to do is another FTP test on the trainer to get a new baseline. My guess is it would be 190watts. which would get me much closer to where I want to be.
Certainly possible. Part of the reason I’ve gotten on the bike is that I’ve developed a bad case of Patellar tendonitis on the right and I can’t really run these days. So it’s certainly possible I’m left biased.
I think I’ll just re-baseline with the Stages and call it good.
Depending on the gear you’re using when you’re on the trainer you should expect 8W to 12W loss from a stages left crank power meter to a rear wheel power measurement. If you’re chain isn’t clean and/or you need to replace your jockey wheels it could be worse than that, I guess.
I once helped a guy set up his three-wheeled bike on a trainer. The difference in power read from an orthogonal array of strain gauges on the crank vs the power read on an optical torque sensor at the rear hub was consistently 24W to 26W. So it can happen.
Test the Neo against a SRM or a third PM if you can and hopefully two of three will agree (unless it’s a SRM which is the gold standard). My money is on the Stages reading high. My Stages was about 20w off compared to my Pioneer dual and the Pioneer was indicting 46/54 split. The same split is also reported by my Assioma Duo. I never tested my Stages (sold it) against my trainer, Elite Drivo, but my Pioneer and Assioma tracked very closely it.
@Erik_Wahlstrom here are the drive train losses attributable to a system with new chainset, new cassette, cleaned chain lubed with additive free mineral oil. Just for your reference. If you’re stages power meter is NOT a little bit higher than your trainer power reading then you should be suspicious.
Sorry I don’t quite understand. How would I know if I’m running in Erg? It is quite noisy with a low grinding sort of sound. How would I pop up a shot?
@Erik_Wahlstrom
What length crank arm do you have?
There should be an option in the Stages app to change the crank arm length. In my case, adjusting the crank length to a shorter setting has allowed me to get the StagesL G3 on my MTB pretty close to my Neo2. I’ve done much the same thing with my 4iiii on the road bike using the scale factor setting.
To test the results I made dual recordings of the ramp test with sprints thrown in during the cool down. The power doesn’t align perfectly of course, but it’s allowed me to get things pretty close from 150 -800w which is good enough for me. YMMV.
It’s been great since I did this as I can jump on any bike and not have to worry about making adjustments on the fly depending on the power source. Having numbers that line up between different sources is the goal in my case.
Before you try and analyse the problem any further, you need to do a dual recording. Do a free ride session (ie not in ERG mode), recording the Neo and Stages simultaneously to separated sources - ie Neo to trainerroad, Stages to your Garmin. Upload both and see what the difference shows. You can use the analysis tool on Zwiftpower for this, or the DCR analysis tool.
Then lets see how the power compares. If I was to place a bet, I’d suspect your Neo is going to giveyou a truer value than the stages.
Do you get a different result when out if the saddle? If the big discrepancy goes away when you are standing on the pedals then that might point point to L/R imbalance being the issue.
Thanks all. I’ve decided to just uses the stages meter. After more reading and riding I think I can chalk up the differences to
Drivetrain losses. When I did the test I’d not cleaned my chain in . . . . Well ever. Degreasing and lube loosened it up.
Leg imbalance. My right is problematic due to injury
Bad testing. I was winging it on the neo.
Since I plan to ride outdoors a lot with power I’ll just stick to the stages ftp meter. I did the Reinstein ride outside with the 216 FTP and it felt suitably hard but not insane.
I encountered the same issue. The Neo 2T gives in average a 20w lower power reading than the stages ( left only). I also have an Assomia duo which gives same reading as the stages. Furthermore when I do a theoretical calculation ( Wolfgang-Menn.de, recommended by GCN) using data from various steep climbs I did on my road-bike the calculated power is very close to my readings on stages/assomia. As those calculations are based on basic physics my conclusion is that the Neo 2t ( at least mine) under estimates power output. If you want to get to the same number you can just play with your weight. In any case the absolute numbers are not that important the importance is the consistency of the measurement so you shouldn’t get too obsessed by the number. Once you know one measures always 20w less you just adapt your settings to that so on my road bike my ftp is 260 and on the Tacx it’s 240
I may have a post way way up there, but exactly the same on my Neo-original flavor. Same deviation 20W or so, deviating higher with higher power outputs and it is not cadence dependent.
Interesting, the 20w difference is quite stable in my case when looking at the average of a training at different watt levels but max power during a session is very similar
The numbers don’t matter as long as they are consistent. Just use which ever power meter you plan to rely on for training. If the Stages is going to be used indoor and outdoor then just use that number.
Fully agree, no rocket science but I split my time between 2 countries, one where I have a bike with assomia pm and another with a bike with stages pm and a Neo 2T and because I happen to like, apart from cycling, to understand data I try to figure out how they compare. I got the Neo 2T only recently and got the impression that indoor training felt so much harder than being on the road. I wondered if it was really harder or if the power measurement was just different. My conclusion so far I that indoor is mentally a lot harder but also that power reading of the Neo is lower. I don’t care about the absolute number but try to compare something that is like for like
