Dual sided or single side power meter

Buying a new road bike this year, 14 years after my Giant TCR Advanced purchase. It’s been a great bike. Will include a power meter for this one. Likely a Tarmac SL8 Sworks frame with Ultrega goup set. Question, does a single sided power meter work just fine, or is it worth the extra cost for dual sided? A side note, we moved to Tuscany four years ago from the States, and riding here is phenomenal. Gotta love the climbing…


I have single-sided on all 3 of my bikes. No regrets whatsoever.


If you like the idea of having a 40/60 imbalance (like I had) then but double sided otherwise go for single sided . .

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It’s looking like single sided will suit me. Thanks!


So it’s looking like single sided is all I need.


Actually I was being sarcastic

Asymmetry in human movement is the exception, not the norm. Furthermore, L/R balance has been shown to vary from day to day, as well as a function of cadence, power, and fatigue. Finally, a 1% difference in L/R balance equates to a 2% difference in reported power.

TL,DR: Friends don’t let friends buy one-sided power meters.


Since you live in Tuscany I’d highly suggest getting a pair of Favero Assioma duos. Reliable as you please, great customer service and I’m a fan of rechargeable so I’m not disposing of batteries semi-constantly. As for single vs dual I’m sorta with The_Cog on this one. It’s hard to say whether years of training with a non-drive PM started this or my abdominal surgery and premature return to the bike exacerbated it but my L/R balance is bad to the point that at times my left leg fatigues before my right and in the 61/39 to 65/35 range. I got my Assiomas during recovery from said surgery (actually ordered the week before) and considering everyone says “you’re probably 50/50 even with a lefty” I assumed it was the pedals and not me. After plying the customer service for months I found out it was me after I put my wife on them and she was bang on 50/50. Considering the Assioma duos are quite reasonably priced and I happen to be a fan of the Look style pedal/cleat I’d say go that direction and get data that maybe you don’t need but would be nice to have just in case. You could also start with their uno and upgrade later to a duo set up.


I got the uno knowing I had the option of upgrading to the duo, but have never felt the need. Actually I just bought a second uno so that I don’t have to be switching them back and forth between my road and gravel bike every other day, as that seemed a more useful use of dollars than upgrading to a duo.

And comparing it to my kickr the uno is very close at anything above 200 watts, so I don’t think there is much of an imbalance I am dealing with.

I could be wrong but other than interesting stats I don’t think a dual sided pm gives you much more perhaps a more stable power reading on a twisty course. Both my pm’s are single sided, and they give me what I want but being a stat junkie if I was made of money I’d get a dual pm. Im sure my non PM leg is 10x stronger how else do you explain the low numbers it gives me :wink:


I started with a single sided PM, but became concerned I wasn’t getting accurate readings after breaking my pelvis and having significant sciatica. So I bought a double sided PM for my next bike.

What did I discover?

My right and left were within 1% of each other on hard efforts, only differing by more than 2-3% on easy sections, and over time, the laterality shifted from side to side.

Crux of the matter was that despite lateralized injury and chronic pain, I was not seeing the differences I expected between legs. So my next two bikes have had single sided PMs. I do still have the double sided Pm on my backup road bike/trainer bike, and can occasionally spot check, but there are minor enough differences between my legs that they could be explained by error.

There is also the question of whether you can train different technique based on laterelized results. In the absence of a strategy to deal with leg differences, what would you do if you did discover, say, a 5-10% difference between legs?


This is good information. Much appreciated. I am also a fan of the Look style pedals/cleat. Until going onto trainer road forum, I had not heard of Favero Assioma PM. Will check them out.

Do you need dual? No
Do you need a PM? No

If you are only running power on one bike, and cash isn’t the limiting factory, just get the dual.

All my bikes are left only and I don’t regret it. I have no plans to ever go dual. And I have no plans on having a trainer with power either. The data between all of my PM’s (Stages, 4iiii, and Vector, the Race Face died) is close enough that I can’t tell a different day to day.


Depends on what you do with the data. Most riders will say “single-sided is fine” because they don’t do anything that requires accuracy (these are the same people who say, “the only thing that matters is consistency, not accuracy”). That’s because training (especially training FTP) is one of the least demanding things you can do with power data (that’s why people have been able to train with just a speedometer or a wristwatch for decades).

A smaller number of riders do actually need accuracy for the things they do and single-sided power meters, while fine for training, don’t typically provide that accuracy.

So if all you’re planning on doing is training FTP, single-sided is probably good enough – since a speedometer and wristwatch are good enough. Accurate power data allow you to do other things that can help make you faster or longer, but not everyone wants that.


My neuroses wouldn’t let me only measure one side of my body. I would definitely think about the power side too much.

Especially since my left quad always hurts quite a bit before my right quad, but it’s not a strength thing. I can press and extend the same weight on each leg independently. It’s something else that I try to ignore. I just don’t know what I’m ignoring. I think it’s due to a weaker left glute from a motorcycle accident, but I digress. It doesn’t show in any strength work but cycling isn’t strength work.

Can you share what those other things are?


Using his method for aero testing is the key one that springs to mind :stuck_out_tongue:


I’ve got a Stages left gen2 because I didn’t have much choice as a Campagnolo rider and didn’t want to switch off Time pedals. Yes, people said Stages sucked back then and a vocal minority will tell you that left only sucks.

I guess it depends on how you use it because I don’t see any problems. I’m usually looking at power meter during sub-threshold intervals, threshold intervals, FTP tests, and VO2 type intervals. Being that my FTP is well tested with the Kolie Moore long form test and then modeled in WKO, I feel that I’ve really honed in on my FTP and that the Stages left provides accurate enough data. If I had a small imbalance that made my FTP show 10 watts low or 10 watts high, I don’t think it matters for how I use my power meter.

That said, I’m building a new bike with an Sram Quarq so spider based, not left only, but not quite full dual power.

What are the options for Ultegra 12 speed? New crankset altogether or a left replacement arm?


Yep. Going faster on a bike is pretty simple: more power, less drag, or smarter tactics. The stop watch and finish line don’t care which, and the rules allow all three. Most riders only use their power meters to do the first, especially if they think the only that matters is training FTP. Measuring drag so you can improve it, and proper identification of your strengths and weaknesses so you can use them tactically, require not just consistency but accuracy.

Lots of people think that agreement within a couple of percent at a single point on the power-duration curve (for example, near FTP) is close enough. If they don’t need accuracy, that’s probably true. Not everyone wants or needs to be faster. Some people just want to look better, and feel better, and lose weight, and there’s nothing wrong with that. Single-sided is probably fine for those folks. But I still ride with guys who are more talented, and younger, and a shade faster than me so I have to do everything I can to stay up. I’m at an age where I’m no longer increasing my power. I’m now at an age where I’m working hard to keep the power I have. I’m old, fat, and slow; but some days, if I pay enough attention and do all this crazy shit just right, I’m just old and fat.