Power meters, Rabbit Holes and Leg Imbalance

Hello all,

I wish I was one of those folks that could make a decision and then go with it instead of spiralling around for a while. :grimacing:

I’ve been reading threads and followed a couple of rabbit holes on why dual sided power meters are no good on Shimano cranks [thanks to GPLama and others on that one]. I’m pretty sure I have a leg discrepancy caused by various knee opps and a trapped nerve and some muscle wastage on the calf on one side (resolved by a back op) so getting a left only [stages gen 3] seems like a waste when there’s good dual options around like the Power2Max crank. As I have two bikes with 105 anything I got wouldn’t be wasted and I only ride SPD pedals so the Vectors and Assioma’s based on what I’ve read are ruled out as to get working SPDs you have to but another set of pedals, possibly trim off your shoe tread etc. - interesting but an amount of fannying about to get there, more expensive along and possibly more problematic when unclipping.

So since it seems to me that the Power2max NGEco Granfondo or Rotor Edition with my own chainrings would give the total power but not a genuine L/R balance - as above I’m pretty sure I’ll have discrepancies but would like to know total power for outdoor workouts and riding.

Any other suggestions as to what I could fit to or replace my Shimano cranks/rings with that would give me this either with more accuracy or true L/R for the money?

The Power2Max seem to get good reviews from what I’ve read and can’t seem to find anything as good for the cash at £537.

Are there any downsides?

There’s a good discussion on P2M here. Most feedback is really good.

I’ve the older generation Type S - pretty much identical to the Eco but lacking Bluetooth. It was an excellent buy. I’ve had it for 5 years now and it just works. The only thing I would say is there is a lack of flexibility with getting a crank spider PM. I got the 130 BCD so I could run a 53/39 on my TT bike. I prefer a 52/36 on my road bike but that would be a 110 BCD, so would need to buy another PM to run that.

I’m shopping around for another PM - though I can’t really justify it at the moment :sweat_smile:. It’ll be another P2M or Assioma Duos. If I get the Assiomas I’ll use their cleats and set aside a dedicated set of shoes just to use with them for them. Save faffing about with altering cleats etc.

I have P2M on all of my bikes and they’re great power meters. Classic, S series and NGeco. Have a little bit of everything. Just went and looked at a workout and my current L/R balance from the meter is 55/45 but I really pay it no attention. I’m not going to try and actively change my peddle technique to try and chase a 50/50 number. I do the workouts and try to do the peddling drills. Smooth and efficient is my goal and I really don’t care about the balance.

No downside with P2M but mentally maybe a downside if you see an imbalance and you think something is wrong with you. If the imbalance is a big delta like 35/65 or something like that, then maybe worth addressing with a Physio but for myself, even if I saw 40/60 on a workout I wouldn’t be concerned.


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Short answer… get a good set of pedals like the Assioma Duos.

Long answer…

I bought a left side only 4iiii power meter this spring, I was debating all winter about dual sided or not and came to the conclusion that I would go left side only as I have Ultegra cranks and the dual sided power meters from any company are wildly inaccurate with these cranks as GPLama’s research shows. Unfortunately for me I discovered that I have LR imbalance where my left leg is much weaker. I’ve never used a dual sided PM yet, so I don’t know the true percentages, but it’s somewhere in the neighborhood of 40/60 to 45/55 depending on power output at the time.

So I started dual recording my rides with my Garmin and the 4iii power meter and the .fit file from TR. I compared them on my computer and I found that at low power my left leg is barely working and is like 15% lower, but then as my power increases into Vo2 max range and above, it evens out with my right leg to an almost 50/50 split.

So I took that information and I adjusted my 4iii power meter to read like 7.5% higher so that my average power over a ride was bang on and thus my calories burned and everything were good. I ran with this setup outside all summer and I did my TR workouts outside. Well as fall approached I compared the power meters again and I found my legs had balanced out by a percent or three and my power meter was now showing me outputting more power than I actually was. What this resulted in was me actually not hitting my marks on my outside workouts in the sweet spot and below range. I ended up re-testing my FTP and it dropped like 10 watts even though I had fully completed my workouts perfectly.

If you knew 100% that your one leg was exactly 5% lower than the other all the way through your power curve then you could absolutely get a left side only and love it. However, if you’re anything like me, it changes drastically and thus making doing actual outside workouts possibly, but not productive. Now that winter is almost here, I’ll be inside on the trainer so I’ll run with it until next spring to which I’ll be looking to get a dual sided meter. If Shimano doesnt have a new crank by then I may look into switching groupsets or getting the Assioma pedals.

I know you said you exclusively use SPD pedals, but if you truly want to have accurate power and don’t want to waste your money on a 105 crank based PM that’s not gonna be accurate anyways, then I think you can totally get the Assioma’s and get used to the Look-Keo style of pedal. It’s actually really nice once you get used to it.

Sorry for the long read, hopefully it helps you make a decision.

For the majority of us, I just can’t understand the need for dual sided PM. I fell for the hype and bought a dual sided system thinking I had an imbalance due to what I read on the internet to replace a perfectly functioning L sided pedal PM. Only discovered I had 51/49 difference.

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Thanks for this but the Power2max replaces the cranks and spindle - the only parts I’d be using would be the chain rings so it should be accurate total power.

I got the Quarq DUB with DA rings. Looks good and is hassle free. I’ve used PW2max and was super happy with that too.

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