Power meter blues - I have no clue what my actual FTP is

To add to what others have said…

It doesn’t matter what your FTP is. FTP is a tool used to guide your training and set your zones. Nothing else. Not the goal, and not a measure of self worth. The number doesn’t matter in real life.

The goal is improved real world performance, which you seem to be describing. Be happy with the results. Real life performance is based off of every other single point on your PDC… plus bike handling, plus your mental game, etc.

If you want a number, then find a segment on Strava that you can go all out on, and then compare how quickly you can finish this as your training progresses.

I will also point out that there is very poor calibration between commercially available power meters. While most seem to be close to each other by like 10-20w, some are way off.

And that’s ok because you care about the results, not the number. Who cares if your z4 work is called 200w on one, and 280w on the other. Doesn’t matter what number you label it with as long as you train it.


If he numbers are not comparable between units, we should stop labelling the values units as watts. If they are truly measuring watts, then they are comparable. Otherwise it’s just an arbitrary relative measure, not watts.

I think there is some value in investigating why the numbers are different. If its just in the power meters, so be it. But it might be, in part, due to other differences in the environment. Cooling, bike setup, etc. The difference beyond the power meters may be addressable.

I have a pretty similar setup to what you’re describing. I have an older bike on my trainer (Elite Direto) and Rally RS200 pedals on my “outside” bike.

What I did to check how the pedals reported vs the trainer was to put the pedals on the trainer bike and have them paired to my Garmin, while the trainer was paired to TR on my laptop. After doing a few workouts with that set up it was pretty clear that the trainer was reading 10-15 W higher than the pedals. After re-calibrating the trainer, the two were pretty well matched.

I had to adjust my FTP down (womp womp) but it’s nice to know that my inside and outside powers are being measured consistently.

Correct. That’s really the best way to think of FTP anyways. It’s just some number used to guide your training zones.

Then the units should not be watts, but the various devices all claim to be reporting watts within 1% or 2%. If they are way off of that, that would be good to know (I’d avoid buying the ones that are way off).

But like i said before, I think it’s valuable to figure what’s due to the power meters and what’s not. It gives you insight into things you may be able to fix.

I was just reading thread on the new AI FTP detection. Nate P says it takes all workouts as inputs (indoor, outdoor, structured or not, workouts from Zwift, etc). Note AI FTP takes all that in, the power levels do not (at least not yet). If my indoor and outdoor workouts have wildly different power, it’s going to raise hell with AI FTP. It would to nice to at least figure out an offset, though I saw on a video from DC Rainmaker that some power meters have more error under higher loads (it’s not a simple offset). In the fall, I’ll put the pedals on the bike with the trainer, and compare them. At very least I need to figure what’s due the power meters and what’s not.

Well, I am assuming TR has far more behind the scenes than they are specifically showing at times. Notably, it seems this just released info may well be related to the whole “power picture” with respect to multiple devices and/or bikes (that leads to “different FTP” due to rider position issues) and the like.

I welcome that because it seems TR has often hand waved the different devices, data, setup issues without any real background or way to deal with it. Would be nice to actually have at least some level of control within TR.


:rofl: :rofl: :rofl:

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I assume you are asking about my 2 year old post. I abandoned using the Tacx and just take all power readings from my Stages. I use WKO5 and you cannot accurately model your power duration curve with two wildly different power sources.

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Stages was the right choice. The wheel on trainers will be sensitive down to the PSI in your rear tire. Lots of reasons they could have been way different.

My Tacx Vortex was horrible - like 30-75 watts off depending on how warmed up it was and depending on the intensity level. I did a lot of testing to figure it out.

What I’ve never understood is how dual power meter pedals can be accurate for measuring dual sided power. Do the companies especially calibrate pairs of pedals so that they are spot on?

Power meter pedals may be a convenient solution for many but I think the gold standard is probably crank based (quark, power2max, etc).

I agree with you on crank based being gold standard. I believe dual side power meters are two independent power meters and the power measured at each is added as opposed to single sided where it is multiplied by 2. Not sure tho

Piggybacking on this thread as it’s related. For indoors I use a Kickr Core, and my road bike has a dial sided 4iiii power meter. They seem to align fairly well. I can push slightly more power outside for the RPE, but that’s probably related to cooling, bike handling, etc. (this topic has been discussed many times). With my old left-side Stages the difference would be about 10% so the dual sided is better (as can also be derived from looking at the L/R balance).

I’m currently considering a left-sided Stages for my mtb as I am planning on doing more mtb rides for the remainder of the season. So I will basically have three different sources of power. For using the devices during training I’m not so concerned. After all it’s just a number…

But I am concerned how this will affect AI FTP. Let’s say I do most of my late season training/riding on the mtb and it’s 10-15% off from my 4iiii og Core. AI FTP uses that number and the occasional turbo-ride will probably be either too easy or impossible to complete.

It would be good if @Nate_Pearson or @Jonathan could comment on the use of multiple power meters and the effect on AI FTP. If it’s just “don’t sweat it, we’re doing some voodoo magic in the software” that’s fine. I trust you guys!

This post above and a new teaser released just yesterday are some clues but not firm answers.

A power meter simply measures force, using strain gauges. While there are variables that need to be accounted for in manufacturing, such as variations in materials between batches, exact dimensions and strain gauge placement within the manufacturing tolerances, etc, these are all taken care of in production calibration. These are not random number generators that need to be matched in pairs, they are force measurement devices that get calibrated against known forces.

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That’s all well and good but we see a lot of variation in power meter readings. What’s to say that there isn’t a 2% difference between left and right pedals? Or one is 2% high and the other is 2% low thus leaving a 4% left to right gap.

It’s just something I’ve been curious about. People talk about left right balance with dual power meters like it’s gospel or some exact reading. It could be just as off as a left only power meter with a right dominant leg.

I still think that a single crank based power meter that gets readings from both left and right legs might be the most consistent.

If they are spec’d at +/- 2%, yes indeed in theory you could have a +2% and a -2%. If your power is balanced 50/50, that pair would measure… smack on, and if you have a 60/40 balance (pretty extreme) coupled with the high-on-high, you’d be 0.4% off. The worst case isn’t the one you mention.

Assiomas are spec’d at +/- 1%, and I suspect the factory output is much tighter than that. Most of that tolerance isn’t for production variation, it’s for accuracy of the measurement vs a “perfect” force measurement.

My vote is for power pedals.

Same power meter for all indoor and outdoor rides.

This is the best solution, if true power consistency is your target. It doesn’t have to be. You can certainly fudge together different power meters. However, if you really do care, a single accurate power source is the ultimate solution.

From my experience, power meters are not anywhere near as accurate from brand to brand as many believe.

Currently, I believe the Assiomas are the best value for money accurate and consistent power pedals. Obviously, this then involves different cleats etc. I really wish I’d bought a set of these at the beginning of my power meter journey.

Since purchasing them I have had a fantastic structured training experience. Both indoors and outdoors. This includes using them on my MTB on gravel rides. 250w is 250w. Indoors, outdoors, on any bike. Previously, I had many poor experiences with different power meters.

Cue response. “All my power meters are exactly the same”