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(Before closing as duplicate, this question is somewhat related but not the same at all: Pedal power meters on off-road / MTB).

Background

I am an avid runner, and am pondering whether I will branch out to biking "earnestly" in the next season. Right now, I have a very nice full-suspension MTB which really feels at home at ascending and descending but rides passable on roads (sure, no speed records, but that is irrelevant to me, for now).

Eventually I see myself getting a proper road/gravel bike, but before I invest heavily into the "N+1", I made a rule for myself that I will buy that only when I have proven to myself that I have fun with bicycle training, and can fit it together with running, time-wise. I will try that on the MTB (on roads/light offroad, not on mountains), simply because I already have it.

Also, I am doing my running training by power with one of those pods that clips to a shoe, and am absolutely delighted about that mode of training. I dislike training by speed or heart rate, and obviously, power-based training is right at home on bicycles. So I'll allow myself to invest into some solution to measure power on the MTB, and if everything turns out well, I'll transfer that on to the eventual "real" bike.

Question

Can I safely assume that there is no inherent problem using one of the common power pedals (something like Favero Assioma) on my MTB and just ride? I found mentions that road-bike power-measurement devices are probably not robust enough for MTB use, but I would not ride the bike anywhere that would be an issue - only on asphalt and very light farm tracks, i.e. only on paths that would be easily within reach of any gravel bike, there will be zero bumps, crashes or jumps. I would switch back to the old pedals if I should go to the mountains in that time.

Is the fact that there is the suspension "stealing" power? I assume that while the power measured by the pedals will not completely arrive at the road, it should be the power my body outputs; measured as accurate as the same device would measure on a road bike. So regarding training (i.e., progressive overload, structured sessions, determining FTP, avoiding over- or undertraining, factoring in inclines and head-winds and so on) it should be perfectly unproblematic, right?

I do not use cleats right now, so there is no constraint there (I would get whatever system is best for the pedals I'd eventually choose).

2 Answers 2

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The most common power meters are

  1. crank mounted
  2. pedals

They both can be single or dual sided, but outside of some niche applications, single sided is enough. I own single sided crank power meters and dual sided Assioma road pedals. I have never looked at left-vs-right data.

Crank-based power meters can be switched between bikes quite easily if the bikes use the same bottom bracket type - and if they clear the chain stays. Road cranks will usually not work on MTBs. Gravel cranks should work on road bikes, but with a slight asymmetry because they are a bit wider than road cranks (I do that sometimes, doesn't bother me at all)

Road pedals are not meant to be walked in, which makes them a poor fit for MTB or gravel rides where you don't always stay on the bike. I wouldn't hesitate to use my Assioma road pedals on the MTB from a durability standpoint ... but I just don't like to use road shoes if I'll have to walk more than a few steps on flat ground.

SPD power meter pedals like the (relatively new) Assioma PRO MX on the other hand would be a perfect fit (I have no affiliation with Assioma, I do not own these, but reviews seem very positive). SPDs (not SPD-SL!) are fine for MTB and gravel riding, and more and more people also switch to them for road cycling. The bigger contact patch on road-specific pedals doesn't really matter once the shoe gets stiff enough. I do all my long distance, multi-day road rides on SPD pedals.

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  • I will use the MTB just like a road/gravel bike for this particular purpose; i.e. on flat or harmless inclinations, good quality roads etc. I had cleats in the far distant past and walking in them is required to me. That said, thanks for all your input! Those Assioma PRO MX-1 did not turn up when I looked at pedals (some months ago, probably before they came out or were reviewed). As long as they have no long-term drawbacks when I transfer them to a gravel/road bikes, they seem like a great solution (and not too costly either).
    – AnoE
    Commented Jul 10 at 13:09
  • On the long-distance road rides I do, I would say the most common pedals are SPDs (mountain/touring type). I use mine for that, plus commuting, gravel, and sometimes MTB
    – Chris H
    Commented Jul 11 at 16:12
  • The bigger contact patch on road-specific pedals doesn't really matter once the shoe gets stiff enough I'm not so sure about that. I certainly feel the difference on my soles between SPD-SL/Speedplay platforms and smaller SPD platforms, even wearing top-of-the-line Lake shoes, especially on longer rides. But I'm also about 100 kg, can still pop 1500W whenever I feel like it, and wear 49s - wide 49s (50s in winter, or whenever I feel like wearing thick socks...). That likely puts me in some "outlier" territory. Commented 2 days ago
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Is the fact that there is the suspension "stealing" power? I assume that while the power measured by the pedals will not completely arrive at the road, it should be the power my body outputs; measured as accurate as the same device would measure on a road bike. So regarding training (i.e., progressive overload, structured sessions, determining FTP, avoiding over- or undertraining, factoring in inclines and head-winds and so on) it should be perfectly unproblematic, right?

The short answer is that yes, you can train with power on an MTB. Your riding position is a bit different from a drop bar bike. If you're acclimated to both styles of bike, chances are your power output will be pretty similar.

The suspension doesn't matter because you are measuring power reported at the pedal or crankset. The suspension should cause power losses riding on the road. Those losses would show up in the bike's speed, not in the power measured at the pedals.

Say you had some tiny Speedplay power meter pedals and you were in street shoes. Imagine that your feet are squirming on the pedals, or you have to exert effort to keep your feet on the pedals. In this case, I would expect there to be losses in the power measurement. That is the sort of scenario that would rob power in a way that shows up at the power meter. That is, for the same metabolic cost, you'd likely deliver less power to the pedals. If you could strap a gas exchange mask to your face and measure VO2 consumption (which is equivalent to power generated by the body) compared to power delivered, I believe you'd see this.

Be aware that the question/answer you linked to is outdated. There are a few more MTB pedals out now, and Favero sells one. Say you convert to a road bike. I tend to prefer road pedals, as there is zero rocking in the cleat system. With MTB pedals, depending on how your shoe tread interacts with the pedal, there can sometimes be a bit of rocking as the cleat wears. However, you might prefer to walk relatively unrestricted when off the bike. This matter is purely down to personal preference; I know several people who go on hard road rides with MTB pedals (usually on gravel bikes).

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    "I believe it's true that on a road ride, the suspension will cause power losses. Those losses would show up in the bike's speed." So would the less aero position of a mountain bike (effort wasted in pushing more air out of the way), and even though you (probably) can and should lock out the suspension, MTB tyres will still sap energy - not just basic rolling resistance but something like suspension bob. They can be swapped. But these all only increase the inefficiency; you can never deliver 100% of your power to the road. And that doesn't matter for training (by power or heart rate)
    – Chris H
    Commented Jul 11 at 16:16
  • All true, but as a reminder, for this question I am not looking at side effects of a MTB (i.e. non-aero position, wider tires and so on and forth) but am just interested if power-based training (using a MTB as a placeholder for a road or gravel bike) makes sense or would be so skewed (for reasons I couldn't think of) that it's nonsensical. Turned out it was a happy coincidence that there are actually pedals out there now which seem to target exactly my use-case. ;)
    – AnoE
    Commented 2 days ago

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