Too bad he didn't snag the Vector 2 last weekend @ $549. Personally I think single sided is fine. I'm fairly constant at 48/52 so as long as it doesn't change much more than a %, he should be fine for single sided.

The closest it'll get for him will be the Favero. Or a spider-type solution that by itself is already around that price.

Power2max starts at $500. Spider based so measures both sides.

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Swimming Workout of the Day:

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2020 National Masters Champion - M50-54 - 50m Butterfly

With the availability and pricing of dual or aggregate power meters, there is really no reason to settle for a power estimator anymore. As Jason said, Power2Max is a good option at $500. Or a used quarq.

The downside to single-sided power is consistent inaccuracy. It is like a broken analog watch-- it is correct twice per day, but just don't know when those moments occur. If he has a power imbalance, then the power will be incorrect by about 2x the % off. For example, if his L/R imbalance is 48%/52%, then the PM would read about 4% low. For example, if he was riding at 250W with a 48/52 imbalance, the PM would read 240W. At least it would be consistent, as long as his imbalance was consistent.

I didn't see the Amazon deal, but if it's for the Ultegra 6800, you can find better deals than that... I got one for slightly less than 300$ recently - I didn't get into details, but I think they are clearing them out for a newer version of Ultegra?

if you really have a choice, go dual sided as it eliminates some potential error and really eliminates wondering if it makes a difference, which is actually worth some money. But, I have some friends who have had great success racing bikes who have used Stages single sided power meters for power training. Most of them got their Stages 5 years ago instead of waiting for dual sided power meters to drop below $1600. The moral of the story is any power meter you can put on your bike today is a million times better than the perfect power meter you might be able to afford in the future ;-) Frankly, I got a Quarq 2 years ago and I love it, but I'd probably be a better cyclist today if I had bitten the bullet and bought a Stages 4 or 5 years ago.

If you friend can swing a dual sided PM in the next month or so, wait. If it is going to be a next summer kind of thing, he will be way better off training this winter on a one side PM than with no PM.

Have a look at the FSA Powerbox, at $596 I think it makes absolutely no sense to pick up a single sided stages.

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That's not strictly true. The 2% refers to the range of accuracy, not how inaccurate the power meter is. So the reading could be anywhere between 2% low or 2% high. It could be absolutely spot on. So using the example above, the left handed power meter is reading the left leg at 120watts and doubling it to 240. 2% either way means that the actual power being put out by the left leg is anywhere between 117.5 watts and 122.5 watts. This then means that the overall reading could be anywhere between 235 watts and 245 watts. If the 48/50 is consistent at all powers then that reading is as accurate as a double sided power meter as the left leg will always be putting out 48% of the overall power and the power meter will give this reading, +/- 2% (which is the same level of accuracy as almost all power meters out there).

That's the issue with single sided, it's whether any imbalance is consistent across all power ranges. The only way to tell is with a TRUE double sided power meter (such as power tap P1 or Garmin Vectors). SRM is not a true double sided power meter, for example. So, you could spend a chunk of money on a true double sided power meter to find that your leg balance is consistent across all power levels. End result, your readings from a single sided power meter will be just as accurate (save for silly situations where you deliberately pedal harder with one leg, or do single leg drills) as a double. Single sided are a compromise and, for some people, not particularly accurate. For many, however, they work almost as well, if not as well as, a true dual sided power meter.

I have no vested interest. I started on a stages and using a stages I improved my FTP by around 25% from when I first bought it. I now own power tap P1s and they give me the same FTP readings as my stages and I've found the only time I am biased is high power, high torque (i.e. climbing a 20%+ gradient). Any other time, I am 50/50. The end result, I could have kept my stages and it would have served me perfectly.

Except most people do not have a consistent imbalance. Most people will have a balance that varies with length of ride, power zone, and other variables.

Agreed, with a caveat. If you really do only have $399 and coming up with $596 (at Christmas time no less . . .) is going to delay you for a couple months one should give very serious thought to pulling the trigger now on the Stages. Not everyone can just snap their fingers and increase their budget by 50%.

You'll get more out of training with a Stages in December, January and February than you will out of having no PM then getting a dual sided one in March.

Yes, R8000.

Yeah you are 100% right.
My comment was based on the OP saying that budget was $500, figured $596 isn't that much of a stretch and you get so much more.
But yes at $399, that's a bigger stretch.

You are combining multiple things... measurement inaccuracy is independent of inaccuracy caused by a user's power imbalance. The manufacture's accuracy rating does not take into account inaccuracies that a user might contribute. Here is a quick illustration to show how a 48/52 power imbalance would result in a 4% error that is entirely unrelated to the unit's accuracy range for a simple measurement:

Left Power: 120W (48%)
Right Power: 130W (52%)
Actual Power: 250W

Stages 1-Sided Power: 240W -4% error (2x L Power)

That left power 120W reading also has a ±2% error range, so the user's actual power could be in the range of 118W - 122W.

It does not matter that imbalance may change during the workout. It introduces yet another variance on top of the inherent accuracy of the measurement itself.

If you add it all up, you might be producing 255W, but the unit might read 240W. Or not. The errors are cumulative. In this example, a single-sided unit has an error range something like ±6%. That is why a unit with total power (like crank, pedals, or a hub) are more likely to be closer to reality than a single-sided meter.
Yes, and this multiplies the inaccuracies of single-sided meters.

My n=1

I bought a close-out Stages one-sided PM for my P2 and pair it with my Garmin 510.

With the exception of 2 battery changes, it's worked flawlessly through the last 1.5 yrs (3 HIMs and 1 IM).

YMMV....but, I wouldn't hesitate to buy another one (and may for my roadie).

Good luck.

As an FYI
Just saw that Power Tap is running some specials.
They have refurbished wheelsets and pedals at $549.
Seems like a crazy smokin deal.

I had 2 sided before I had one sided...largely because I was curious post left knee surgery. I normally see 50/50 occasionally 48/52 at worse. The more climbing I do typically all 50/50.

Using Vector2 and Stages v1.... just got Vector3.. so that will be going on the road bike.. V2 will be going on the TT bike and the stages will be going back to the wife's bike. For me I dont have an issue with one side because I dont do the type of workouts where dual is needed or something better then stages is required.

PowerTap C1 @ $349. Basically a no-brainer at this price point.

https://www.powertap.com/...amp;utm_medium=email

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The point is, ladies and gentleman, that speed, for lack of a better word, is good. Speed is right, Speed works. Speed clarifies, cuts through, and captures the essence of the evolutionary spirit.

I'm too superficial to run those rings :)

The greatest value of training with power is the objective measure of effort and a single-side power meter can do that just fine.

My latest Quarq DZero offers R/L metrics - I've looked at them once or twice and didn't see anything particularly interesting and continue to just look at the Averaged/combined figure to gauge my efforts. Of course more features is 'better' but if you're shopping on a budget I would say L/R metrics are a ways back on the list of priorities. After all - we rode with a single watt figure for ~ 10 years once power meters became commonplace.

If you're an aspiring pro, or maybe have some injury history the priorities might change - but for a typical age grouper, single side power will be helpful over no power.

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" I take my gear out of my car and put my bike together. Tourists and locals are watching from sidewalk cafes. Non-racers. The emptiness of of their lives shocks me. "
(opening lines from Tim Krabbe's The Rider , 1978

You seem to be confusing power meters that only measure the power of one leg with those that measure that of both combined.

As someone else pointed out upthread, the error of the former is equal to the technological error PLUS twice the variation in L-R balance. The latter in turn is not necessarily constant, but can vary based on exercise intensity, cadence, fatigue, etc. Net-net, such devices really aren't worth much, especially for a triathlete who is presumably most interested in their performance over longer durations, in which, e.g., heart rate can be a reasonable indicator of intensity.

OTOH, unless you are attempting to diagnose or rehabilitate an injury, I don't really see any use case to be made for power meters that measure and report the power of both legs separately.

(Then there is your Quarq, which can only pretend to differentiate between the contributions of your two legs... that's a "feature" that can be worse than what you pay for it even it is free.)

Far be it from me to argue with the guy who wrote the book on it!

Thanks for the clarification Andrew

In fairness (and upon review), it was really only your first sentence that threw me. Otherwise we said essentially the same thing.

Using the pseudo L/R balance reading's from my Quarq, just in the last week I've seen differences of up to 2.6% in my left leg power. So potentially a 5.2% difference in what a single sided power meter would report. None of my rides in the last week have had the same L/R balance, and there isn't any consistency to help account for those differences.

I don't see the point in spending money to buy a tool that is meant to accurately track your training and fitness (among other things where accuracy is important) when you never know when it's accurate and when it isn't. Unless of course you've done extensive testing on yourself and can anticipate your L/R balance and it's potential fluctuations...but you'd need to ride A LOT with dual sided PM to do that first to even know if it's possible.

You're using an estimation for an extrapolation.

Here's what I don't get.....all the talk about left vs dual, 2% vs 4%, etc etc....

AS long as it's consistent, and you use the same PM to measure your FTP as you do to do your FTP based workouts, isn't that what counts for training?

What happens if your PM dies and you need to get a new one?

re-test so you have a number for the new PM. You "should" be able to figure out what the numbers should be, as long as the meter is accurate. In theory anyway, I don't have a PM "yet".

It's a little like switching between short course and long course in the pool. The times will be different, but you still can use them once you know what you are capable of in both formats.

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Swimming Workout of the Day:

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2020 National Masters Champion - M50-54 - 50m Butterfly

Yes, mostly. If your L/R balance is generally consistent, then a single-sided PM is pretty good for a training and race management point of view. But, if your L/R balance varies, then it can get wonky, and accuracy can easily swing by 5%-10%. That could be an error of 20W when you are doing a ride in the mid 200s, and it could mess with your mind. Say, on a day when you are rested and your balance is 50-50, intervals at 250W feel easy. But, on a day when you are fatigued a little, and your balance is 47-53, it would double-down on you, and the PM would show 250W when you were actually riding 266W. That is just mean.

In general, a single-sided PM is better than no PM. But, these threads do tend to get binary, and single-sided gets labeled as worse than no PM. You just have to know the limitations of a single-sided PM-- that if your L/R balance fluctuates, then the consistency of the PM can be way off from ride to ride.

I think that what AC said was (paraphrasing) that for relatively steady state efforts (where a single sided PM is pretty good) a HR monitor works just as well. If they aren't steady state, then the LR balance can change quite a bit.

With the price of power meters that actually measure total power now, I don't see the point in single sided.

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Swimming Workout of the Day:

Favourite Swim Sets:

2020 National Masters Champion - M50-54 - 50m Butterfly

This was going to be my answer as well. Just like if someone decided to go from one dual sided power meter to another (say P2M to Garmin Vectors), you'd always do a fresh ftp test to get an accurate baseline.

Going back to the pool analogy, it's like swimming at Centennial. You need a different standard for swimming in lane 5. (or is it 2? the second one from the far wall in the shallow end, anyway). The current. Oh god that current....

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Swimming Workout of the Day:

Favourite Swim Sets:

2020 National Masters Champion - M50-54 - 50m Butterfly

Weird, I always noticed it mostly in the far lane (whatever number it is) in the deep end!
I also enjoy getting cloths-lined by others in our club with a wonderfully wide recovery stroke....

I rarely swim in that lane, so I never noticed it in the deep end.

Sorry for the hijack, folks. continue on.

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Swimming Workout of the Day:

Favourite Swim Sets:

2020 National Masters Champion - M50-54 - 50m Butterfly

Which is exactly what a single sided PM does. Extrapolates your total power based on the assumption that your L/R power is even and doesn't change within a ride, or from ride to ride.

The difference is that I don't use the L/R power estimation from my Quarq to do anything, where people who chose single sided PMs use their estimation and extrapolations to guide their training and racing.

This is what I was thinking too. I'm still confused about what to do. :)

I've been running left crank Stages on my bikes for 4 years, and have enjoyed it tremendously. It's helped my training and also the few races I've done so far. Now I'm trying to figure out if I should put a LR Stages on my new bike, or just single side again. It's really just a matter of money. Is it worth the extra money, will it make a significant difference in my training and racing, or is it just a nice-to-have (which would certainly be a gotta-have for a pro)?

I have a Stages and can't recommend it. While its a solid product I have 2 issues with it:

I have a hypermobile SI joint in my left leg, which means after being on the bike I get bad sciatica and snapping hip effecting my left leg power. Last hour effort I did for the last 15 minutes I could only put power into my right leg, so whatever power the Stages showed was off. While that is an extreme example many cyclists have similar issues, sometimes being so minor its unnoticeable.

For TT's its fine but for drafting, it can be off. For example if you accelerate in to draft and pedal 5 times, that first one always has the most force. So the Stages could read 1000w, 500w, 500w, and normalize that or 500w/ 500w. That sounds petty, but in a crit I could do that 50 times and depending on what leg I use first, the reading are going to be different.

What's missing from the bolded statement above is "and as long as your L/R balance is consistent within a given ride, day to day, week to week, at different points in your season, fatigued vs tapered, and across all effort levels."

That is a huge unknown for most people, because they only way you can find out for yourself is to use a true L/R power meter for an extended amount of time (months or even years)...in which case you're already gotten past the point of considering a single sided PM. And most studies that have been done to test L/R balance across multiple athletes show that most athletes are not consistent in their L/R balance in any given ride, day to day, or across multiple effort levels...nor is it predictable.

Accuracy matters. Not just precision. Why?

1. If you ever ride a smart trainer or upgrade/swap power meters. You don't need to adjust your FTP, zones, power numbers, etc. This could have a big effect on TSS, CTL, etc.
2. Estimating or getting an idea of how aero you are (whether that's just comparing wattage and race times with other folks, the chung method, or best bike split)

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blog

Good points. So...accuracy...on that topic, I wonder what the current factual knowledge is about how accurate Stages PM's are? I've read some reports in the past and heard about inaccurate power readings (not just data dropouts, but current, avg and peak power measurements), but haven't really seen anything that definitively supports the complaint. Was this a past issue that's now been resolved with the newest tech they offer? I'm used to using Stages, and have it on my other bike, and don't want to switch unless there's a solid reason to do so. No need to switch unless there is some advantage to making a change. If we're talking about accuracy, and the left-only VS L-and-R is in discussion, we should also take into account the overall accuracy of the PM itself.

The instant your L/R balance is not 50/50, Stages total power reading are inaccurate, no matter how accurate the strain gauges in the left crank arm are.

From what I seen though, Stages strain gauges operate at the same type of accuracy (1-2%) in measuring power on the left arm as most other power meters. The problem lies that they take that left arm reading and change that into a total power reading, which may or may not be accurate.

So let's say you're within 5% avg left-to-right in terms of power balance across your training, and there are exceptions during fatigued instances when the imbalance becomes more significant...If that's your natural physiology, and if you're not riding professionally where it's critical, where does the practical benefit of a L-R setup come into reality? I'm a little geeky and have learned a lot from using my Stages PM and power graph during training, but I guess I'm having a bit of a hard time justifying whether a L-R setup is a nice-to-have or a gotta-have. I know that can be subjective of course, but unless there's something compelling that puts it into the gotta-have column for club racers who use PM's, it would seem the money could be allocated in other areas of need where there could be more realizable gains. (If money was no object, we'd all just get everything, wouldn't we, and get plenty of sideways glances from our spouses, haha.)

A L-R setup isn't what is important, but rather one that gives you total power. You don't need to know what your balance is, just what your total power is.

My PM gives me a L/R balance and I have examples where (on the trainer) I shifted gears in the middle of an interval and simply changing my cadence flipped my balance from left dominant to right dominant. Even though I was putting out the exact same total power, a left only PM would have reported a wattage difference of 20w.

5% is actually a pretty huge swing, but lets go with that for the sake of this example.

When you do your FTP test, lets say you are putting out 50/50 power. 125 watts in each leg, so your test result is 250 watts regardless of whether you were using a one sided PM, or a PM that measures total power. For simplicity's sake, lets just say your FTP is 250.

Based on that test, you set up intervals to do at 110%, so your target is now 275 watts. But while doing intervals, you have a 5% swing in balance as you suggested. So lets say 45% on the left leg and 55% on the right leg. In order for you to hit 275 watts using a left only PM, you would have to put out 137.5 watts on the left leg. But if 137.5 watts only represents 45% of your total power, you're really putting out 305.5 watts (137.5 left, and 168 right). Your wattage output would be telling you 275 watts, which is your target, but in reality you're doing 305 watts, or over 120%. Lets just say you're likely going to blow up before your intervals are done, and left with more questions than answers as to why you failed your workout so miserably. You're going to start blaming your running or swimming schedule, how much sleep you got, your diet, hydration, etc. Then next week your L/R balance is going to be closer to 50/50 and you're going to wonder if all those changes you made to your running, swimming, sleep, diet, and hydration were the reason why that same workout is now much more doable. When in reality those things had nothing to do with it. You just had a PM that was giving you inaccurate power numbers due to unknown and unpredictable changes to your L/R balance.

If that's a tool you feel worth spending money on...go for it I guess.

If you are new to power, I think a left sided powermeter is a fine way to start. Not everyone needs a $1000 option right away. Obviously if you get more serious, I think moving to a L/R power meter makes sense.

The good news is all these new systems Vector 3, 4iii, Stages are all offering upgrade paths where you can start off with a left-sided powermeter and then move to a dual-sided one down the road. Just make sure you get the 2018 models of 4iii or Stages.

That's an enlightening way to paint the picture, thank you!

I would agree with everything that JasonN has said, and for reference my L-R balance can vary by up to 8% (though it tends to vary by closer to 4%) both within rides and day to day.

I think it really depends on your intended purpose. If you just want to track your changes in fitness so you know how well your training programme is working, that's one thing. If you are going to be using it to modulate power output for pacing purposes in a race, that's another thing. You just have to look at how flat the TTE curve is to see how small wattage differences have a huge effect on how long you can hold that pace for.

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Swimming Workout of the Day:

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2020 National Masters Champion - M50-54 - 50m Butterfly

I would disagree (respectfully!!). As JasonN's example, if I aim to do an FTP session at 100% FTP and my balance is 4% different (which it is every ride), I could be trying to hold 30 watts too many at FTP. I'll fail, and wonder why I'm going so badly. If your balance always stays constant, then I agree with you, but if your balance changes then I think a single sided power meter is worse than no power meter. Unfortunately you won't know unless you have a dual sided power meter!!!

Well, if you are monitoring fitness changes then you really want to be looking at general trends over time, not putting too much stock in any one day. So that 4% balance issue should average itself out.

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Swimming Workout of the Day:

Favourite Swim Sets:

2020 National Masters Champion - M50-54 - 50m Butterfly

I guess if you can get past the demotivation that not meeting power targets would likely cause (for me at least!) then you’re right, they probably would balance out over time. I think if that’s all you’re planning on using a power meter for then you’re maybe wasting your money though? I suspect HR vs speed or time up a local climb would be as useful.

I agree with that, which is one of the reasons I don't have one (yet). I want a decent PM that I can use to accurately pace in a race. Which means I'm waiting til I can afford the one I want (probably vector 3)

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Swimming Workout of the Day:

Favourite Swim Sets:

2020 National Masters Champion - M50-54 - 50m Butterfly

I have/had Stages, Quark, Powertap and SRM. I know I am one of the few, but Stages is the one I would be most likely to buy again. I have never had even a single ride that was worse that 49/51 and don't even look at the balance anymore. The Stages simply has the best cost/benefit for me. Contrary to previous posts, I have not found that balance changes from ride to ride or within a ride. YMMV.

It is certainly a case of for some people a stages would be fine, for others it won't be. The issue is, how do you know if it will work for you unless you have previously used a dual sided? Out of interest, ignoring that aspect, why is it the one you would most likely buy again?

I get everything I need from the Stages for a lot less money. You are correct though, if I had never had a dual sided meter, I would want one to know if my power was balanced. However, I am also not sure what I would do with that info once I had it.