As they say, YMMV N=1 etc, but here's a reply I made to another thread that is relevant to your question.

https://forum.slowtwitch.com/...ost=6888688#p6888688

thanks. that's helpful. that seems like a big imbalance. I don't feel like I have a big imbalance but obviously I don't know. I am certainly interested in what my actual power output is vs just doubling what my left leg is doing which could be way off or I could have a 51-49 imbalance which wouldn't be much of course. So a powertap hub would be fine but that's more expensive and not as easily swappable between bikes

I have used both single-sided and dual-sided power meters over the years. Right now, I own two dual-sided and one single-sided. The readings I receive from the three power meters do not differ in a meaningful way from each other. As far as I can tell, my numbers come out within the 1% margin for error. Two are trouble-free latest generation Stages meters and one is a Garmin Vector 2 dual-sided.

My dual-sided meters tell me about my leg power imbalance and about the differences in where my power is produced between my two legs. The first time I saw these things, it was interesting. It told me that my leg with a surgically repaired knee is almost always 2% to 3% stronger than my "good" dominant leg. It also told me that, while I make more peak power with the right leg every rotation, I make power around more of the arc with the left leg. But . . . I have yet to find any way (or really any reason) to resolve the imbalance or make my right leg produce more power around more of the arc without adversely impacting my power production. In other words, dual-sided meters give me more information, but I really haven't found the information useful in any practical way. Both single- and dual-sided meters give me accurate power numbers.

Do you NEED a dual-sided PM? No.

I switched from a 4iii to favero assioma pedals and have been very happy. What is really nice is having consistent power readings between indoors and outdoors and on whatever bike I happen to be riding. I do interval workouts and races on multiple bikes, so it's nice to have consistent power values. I had a powertap in addition to the 4iii. I was able to figure out that I was slightly stronger on my right side, so I calibrated the 4iii higher, but that resulted in the 4iii having overinflated values on anything under 4 minutes. Also, some rides I'm 49/51 but some rides I'm 50/50. With the 4iii, sometimes the power was completely accurate, sometimes not.

If you're just using a power meter to track TSS, then single sided is fine. Your zones on single sided will be probably fine as well. But I've been glad I went with the dual sided assioma. Have had zero issues in thousands and thousands of miles.

Lots of people think that if the people they know have insignificant pedaling asymmetry they will too. Many of them are right.

well I'm hopeful that my stages PMs on two different bikes are pretty comparable in terms of accuracy as well as my 4iii left crank PM on another bike. I think they are based on feel as over time one gets a better sense of what a certain power output feels like over x amount of time. I leave my TSS tracking to my coach. ;) and I know my coach runs stages PMs and is not really concerned about it. I think power during a race for me is definitely more important for the half and full distance triathlons making sure I'm not overcooking the bike. sprint and olympic is more all out so not as important. I'm probably okay with single sided but the price point of $650 for the assimo's is tempting.

I used to have a Quarq until I sold the bike. From that I learned my balance was within 1-2% of 50/50 almost all the time, and that I wasn't going to do anything to try to nail it at 50/50. With that, I ended up getting the Assiomas on my new bike (the UNO single side). I know that if I feel the need to have dual side that I can buy the other Assioma pedal and make it that way (the DUO). To date I haven't felt the need, the pedals have worked flawlessly, and for me they have been a good path. I think it comes down to how much you really value/want that dual sided accuracy...but I can at least vouch for that PM to be a great value and quality so far.

I have never had a single-sided PM, but I can offer some perspective on both Assioma and the dual power thing. First, the real question is total power versus single-sided power. (The dual sided thing is just gravy.) Crank PMs, and hubs, for example accurately capture total power.

The issue is that a single-sided PM will be wrong by the total percentage difference (or 2x the difference from 50%) of your imbalance. So, say that you have a 52%/48% power balance. Your single-sided PM will be wrong by 4%. Further, your power balance will change depending on load, so at the end of the day, a single-sided power meter with a stated 2% accuracy may really be an 6% to 8% accuracy PM compared to a total power PM.

Next, I just upgraded from PowerTap P1 pedals to the Assioma Duo pedals. I freakin' love the Assiomas. And, the price was amazing. I almost bought a second set for my road bike, just because they were so cheap and good. But that would have been stupid, so I didn't.

they seem to have good reviews and dcrainmaker seems impressed with the how focused the company is on improving the product.

yes. I probably should have said total power. I honestly don't care much if I have an imbalance unless it was significantly out of whack indicating I have some other issues to address. the pricepoint of the assimos and the good reviews has definitely got my thinking more about getting them.

I have a 48/52 imbalance. But during hard efforts, it can swing to 45/55. I have P2 dual sided pedals. It made a difference when I zwifted using blue-tooth, because blue tooth would only pick up one pedal, and double the power. If I picked the left pedal, during hard efforts I was getting 90% of my total power, if I picked the right I would get 110% of total power. The error may seem insignificant, but for me, at FTP, it's a +/- 25W; and makes a difference for races.

Interestingly, the P2s over Ant+ send the total power.

Perhaps you should get your right leg surgically repaired to get back in balance and increase power? ;-)

More expensive than $650? I see the PowerTap G3 hub lists for $400: https://powermetercity.com/...-g3-hub-power-meter/

Kinda random, but you reminded me of this video of Alex Honnold testing his grip strength a few weeks back:

https://www.youtube.com/watch?v=UjFw-CXFby4


Short version, sample set of one, but his non dominant hand was ~12% stronger. COMPLETELY just guessing here, but I wonder if there's something going on with the dominant limb needing less power due to dexterity. Just throwing thoughts out

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JustinDoesTriathlon

Owner, FuelRodz Endurance.

That’s the hub alone. So then add the cost of building a wheel around it whatever that would be. And less swappable in that if I have one bike with rim brakes and one with disc brakes then there’s another issue.

Cop out answer...it depends.

Nobody really knows for sure if they would suffer from inaccuracy of a single sided PM due to an L/R imbalance or a fluctuation in that balance until they get a dual sided PM.

I have a Quarq that does "psuedo" L/R balance measurements. I never look at them while riding, or after a ride because honestly I don't care about L/R balance as long as my PM is capturing total power. But for the sake of this thread, I'll look back. Again...this is "pseudo" balance measurements

3/19 - 50.4/49.6
3/18 - 51.7/48.3
3/17 - 50.5/49.5
3/16 - 50.4/49.6
3/14 - 51.3/48.7
3/13 - 52.1/47.9
3/12 - 51.5/48.5

Doesn't seem too bad I guess. But there is up to a 1.5% difference, which in turn means a 3% possible variation in total power output. 3%, on top of the 1-2% possible just from the PM itself seems like a pretty big variation to me. Would I spend $350 on a PM that has an accuracy plus/minus of 5%? Nope. I rather pay a little more and simply worry about calibration. Then sleep easy that my power numbers are 1-2% accurate.

I don't think I'd be worried about that "imbalance" but yes, total power is more my concern. I think if I was having some discomfort/pain that I could attribute to a leg imbalance maybe I'd be more inclined to get a dual sided PM or at least a PM that measures total power. I do have a cleat shim for my right pedal due to hotspots I was getting after riding over 4 hours but that doesn't mean I have an imbalance. If a holiday sale came along and the assimo's where like $550 I might have a hard time not buying them

It depends on how important the immediate and accuracy of your total power is to you. I've had several Stages, a 4iiii, 3 Powerap G3s, and a Power2Max. I also have access to a Computrainer a couple of times week in the off season. I "felt" like the single leg options were good enough for TT pacing, but I wouldn't want to use them for training at specific watts.

I believe that the single leg options are accurate. That is, they always tell you double what your single leg power is. Over the course of 3 different 2 hour rides, their average was within 3w of the Powertap and the Computrainer. What I noticed was there often was a large difference (>50w) depending on the efforts. Single leg meters tended to read high for low cadence/high power efforts and low for high cadence efforts. This tells me that my left/right imbalance isn't static.

If I were to go with single leg, I'd choose the entire Praxis crank. $575 for the crank and rings, bottom bracket and 4iiii powermeter.

I like Powertap and Pwer2Max better, though.

I went with single-sided power meter solution (for now) - Favero Uno. Purely a short-term cost/benefit decision...

Road bike is disc and tri bike is rim. So a hub-based solution would have been 2x the cost [bzzzzt]. On my tri bike, I recently moved from 170 cranks to 155 (Cobb). Started investigating what it would take to get some type of crank-based solution on those. Became apparent to me pretty quickly that was going to be a nightmare (and I'd still need another one on my road bike) [bzzzzt]

That left pedal-based solutions. Looked at the "big 3"-- and from what I saw, Favero looked like the best overall value of all of them. Decided that, at least for now, a "left leg power x2" number would be good enough given the cost savings (and that an upgrade from Uno -> Duo down the road would be pretty simple - just throw more $$$ at 'em). Used the cost savings to fund my short cranks and a new saddle that I finally feel comfortable on (ISM PN 1.0) - while staying within a budget for now that avoids the added cost of divorce lawyer.

I do recognize that my absolute wattage my be off from "reality" by some meaningful amount; however, over time I would expect that at least the relative power numbers would be consistent and meaningful. Couple years down the rode if I get more precise on my power zones/training, then I'll upgrade. YMMV.

I really like the data I get from my Garmin pedals (vector 3). Particularly since I have recently been doing work on pedaling technique with a focus on activating my glute and driving my heel (saw an immediate and significant power increase from this).

My right leg has a longer power phase by 7-12° depending on the day and all of it is at the beginning (likely due to left ankle stiffness/ROM discovered during my last bike fit) of the phase. However, my left leg consistently has a 4° longer peak power phase to more than make up for it. This means I am typically around 50.5/49.5 L/R balance but that will occasionally swing to 49/51 or 52/48. When this happens, I can either identify one leg as simply being more tired than the other or if that's not the case, I know to focus on activating that leg a little more so that power balance returns to normal.

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-Bryan Journey
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