Thoughts on multiple bike/PM combos using TR and smart trainer

I am in the market for a new power meter for my cross bike. After much deliberation, I’m going to go with a Power2Max spider based. My road bike currently has Assioma pedals and the pedals are what I’ve been using with TR using power match. Here’s my question and potential workaround. I’ve done all my FTP tests and workouts with the Assioma. So if I throw my cross bike and new P2M on the trainer, the power readings will be off. My thought is that I can put both power meters on my cross bike and do a few rides, then analyze the power readings myself to find a differential, maybe even at a few different power levels if the slope is off by a good but. Once I have a differential, I can adjust the TR workout based on what bike is on the trainer.

For example: If the Assioma is 10W higher at 200W and 15W higher at 350W. That’s about 5% at both. When I mount the cross bike, I just lower the TR intensity to 95%. This way I can switch bikes if I feel like it and get the same TR workout. Maybe this could be a feature in the future for TR. Have multiple bike settings with an FTP for each, and you just select the bike and the workouts will be adjusted automatically. Anyway, I figured if I get a PM for my mtb as well, I can repeat this process with the pedals and mtb PM and get a similar offset.

What do you guys think? Or should I just stick 1 bike on the trainer and do an FTP test and stick with it?

Edit: spelling

Yeah, I think that’s a solid solution if using 2 different bikes on the trainer is worth the hassle

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What I do is this. Perform an FTP test with the alternate bike/meter, but don’t accept the result so that it doesn’t enter the FTP history if you want to keep your FTP history consistent (but make a mental note of the FTP from the test). Then when you use your alternate bike, adjust the workout difficulty to the same ratio of the two FTP values. For example, primary bike FTP is 250, alternate bike FTP tests at 240. 240/250 = 0.96. When training on alternate bike, adjust workouts to 96% difficulty.

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Two drawbacks to this approach:

  1. Your TSS, IF, NP and other FTP based metrics will be off using this approach when using the P2 max.
  2. Your friends might tease you for consistently not matching the prescribed workout :stuck_out_tongue_winking_eye:

Is there a particular reason not to just leave one bike on the trainer, at least for long enough periods of time that you could just go into settings and adjust your FTP based on the power meter used?

Your road and CX positions can’t be that different that it matters which bike is on there. If it were a TT bike I would understand.

I exclusively indoor train on an old bike that I would never ride outside.

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Did not think of this. I forgot TSS is based off FTP (indirectly) and this would mess with things.

Not really. My position on both is pretty close. I’d probably have the cross bike on the trainer most of the summer so I can ride out on the road bike, and vice versa during cross season. Though that creates the TSS problem anyway if the PMs are that different. I think knowing the offset is good. But what I’ll do with it, I don’t know.

I would say it’s worth doing the comparison and then evaluating from there. The difference maybe very small and you may even be able to get the PMs to read identical by using an adjustment factor. You could alter the crank length value for the Assiomas until the power matches and then just make sure you base FTP on that modified power reading.

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One thing I forgot to add, after the workout you can adjust the FTP for that session to the FTP of the alternate bike. Your metrics should all be corrected for the new FTP.

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Here’s a link to Nate’s response when I asked about it previously.

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That makes things easier.

Do this and map out the differences at a variety of different power levels and then plan accordingly. I have a Power2Max and Powertap P1 pedals that happen to line up within 1-2 watts across the entire power curve so I don’t really have to worry about all of the things you’ve considered.

Do your mapping first and then figuring out your best path forward will be easier. Perhaps you won’t have to do anything at all because they are so similar - no sense building out a theoretical plan until you know the actual differences

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So… I got the new power meter (Power2Max) and mounted it on my bike along with the Assioma pedals. I then mounted it on my trainer and did a workout recording on 3 different devices. Using DC Rainmaker’s Analysis tool, I found something interesting things.

I had always assumed my Direto was off high, based on a left sided Pioneer PM I used to have. The Assioma pedals were always around 6-8W lower than the Direto as well. With that said, I was thinking the P2M would be lower, too. But it was spot on with the Direto, to the half W in an hour workout. So the Direto and Power2Max were spot on in sync, while the Assiomas were low by 6-8W. Looking back over some outdoor rides with the Assioma, my L/R balance isn’t 50/50, favoring my right leg a bit, which may explain why the Pioneer was lower.

The shallow person that I am, the first thing I thought of was, oh man, I did my FTP with the Assioma, I’m losing out on free watts. If I use the P2M I’d instantly be 6-8W stronger. I know, I know, that’s not how it works. Really, all that’s going to change is that when I use the P2M, I’m just going to edit the ride with a higher FTP. That should work right? And it’ll only change the FTP for that ride?

You never said what kind of trainer you have - but assume you’re using some direct drive, smart trainer since you talk about power match.

Here’s something radical - just use the trainer power and don’t care about the numbers. That way you always have a baseline to do your workouts properly without care what bike is on the trainer. Turn-off power match too. :wink:

Yeah the numbers are gonna be different on the road - but seems like you’ll already have a mapping on the offset to them to make a calculation if you need to.

Don’t worry about the TSS calf’s and junk. They will be close enough.

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Most (if not all PMs) allow you to manually adjust the calibration. Run them all at once (or two at a time if you can’t record output from all three simultaneously) and compare the readings, then adjust so that they are indexed against whichever PM you prefer. This should allow you have accurate TSS. It is purely arbitrary which one you choose to index against, but consistency is the most important factor.

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Yea it’s a smart trainer, Elite Direto. And maybe now I will take that advice of using the trainer power. But before, it made way more sense to power match with the pedals as they were the only power source. Either way, I have the offset so I can adjust as necessary.

Keep in mind measurements at the wheels are supposed to be lower than at the pedals/crank due to the losses in the drivetrain ( 1~3% typically). The measurement at the wheel is what is actually moving you forward and the measurement at the crank/pedals is what you are actually putting out. Either is appropriate to train with, as long as its consistent

That’s why I found it weird that the pedal power meter was the lowest of the group.