Power Meter - Crank vs Pedal

Discuss light weight issues concerning road bikes & parts.
TobinHatesYou
Posts: 4014
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

RossLB wrote:
Tue Apr 30, 2019 2:41 am
It really depends on how far out your left/right balance is. Mine is about 54/46. If I used the left power meter on one bike and the right on another bike, they would be different by 16% (108% vs 92%), and both would be inaccurate by 8% but in different directions. This would be too unreliable for training purposes. But if you are much closer to 50/50 it might be less of an issue.
Keep in mind that your L/R balance can change depending on fatigue, cadence, power level, position on the saddle (do you creep up during climbs for example,) incline, back/hip angle, or any combination of those. It can also skew if you race a lot on courses with only right hand or left hand turns like crits.

IMO unless one is super cash strapped and just getting into structured training, they should skip single-sided PMs and wait until they can afford something that measures total power or dual-sided power. Assiomas are just US$650.

cdncyclist
Posts: 79
Joined: Wed Feb 17, 2016 12:10 am

by cdncyclist

TobinHatesYou wrote:
Tue Apr 30, 2019 3:50 am
RossLB wrote:
Tue Apr 30, 2019 2:41 am
It really depends on how far out your left/right balance is. Mine is about 54/46. If I used the left power meter on one bike and the right on another bike, they would be different by 16% (108% vs 92%), and both would be inaccurate by 8% but in different directions. This would be too unreliable for training purposes. But if you are much closer to 50/50 it might be less of an issue.
Keep in mind that your L/R balance can change depending on fatigue, cadence, power level, position on the saddle (do you creep up during climbs for example,) incline, back/hip angle, or any combination of those. It can also skew if you race a lot on courses with only right hand or left hand turns like crits.

IMO unless one is super cash strapped and just getting into structured training, they should skip single-sided PMs and wait until they can afford something that measures total power or dual-sided power. Assiomas are just US$650.

I completely disagree - I know, you get a lot of opinions, but there is reasonable evidence that training appropriately with power (not specified single of dual) improves performance. I have not seen similar data on the incremental benefit of training using single sided vs. dual sided power. Not clear why someone should wait (and lose out on benefits of training with power) for something more expensive that may not be all that much better? Just to be clear, not looking for anecdote (I have my own having used both single and dual), but interested in knowing if there is any evidence on this (which I think would be really interesting if there was!). If costs are similar this might not be an issue, but sounds like there are several trade offs you are considering - my question is whether it worth it.

Good point about L/R - I don't know the cost of stages etc. but you might want to check out buying 2 single sided PM (i.e. both left crank arm) so that what you are measuring is consistent. Unless you know your balance already.

by Weenie


ome rodriguez
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Joined: Fri Feb 24, 2006 9:16 am

by ome rodriguez

Get crank based powermeters. I regret selling my srm for garmin vector 3

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micky
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by micky

Any specific problem?

ome rodriguez
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by ome rodriguez

Power spikes and drops even with the new battery covers. Also tried the cork inserts, was better but when the cork thins down then back to the same problem. The srm was ‘install and forget’

deepakvrao
Posts: 142
Joined: Mon Feb 21, 2011 4:44 am

by deepakvrao

RossLB wrote:
Tue Apr 30, 2019 2:41 am
It really depends on how far out your left/right balance is. Mine is about 54/46. If I used the left power meter on one bike and the right on another bike, they would be different by 16% (108% vs 92%), and both would be inaccurate by 8% but in different directions. This would be too unreliable for training purposes. But if you are much closer to 50/50 it might be less of an issue.
Mine is also about 56:44 or so, when I am doing a hard ride. When just tooling along, it goes as high as 59:41. I thought that is rather strange?

TheDoctor
Posts: 44
Joined: Sun Dec 17, 2017 9:56 pm

by TheDoctor

deepakvrao wrote:
Tue Apr 30, 2019 4:25 pm
RossLB wrote:
Tue Apr 30, 2019 2:41 am
It really depends on how far out your left/right balance is. Mine is about 54/46. If I used the left power meter on one bike and the right on another bike, they would be different by 16% (108% vs 92%), and both would be inaccurate by 8% but in different directions. This would be too unreliable for training purposes. But if you are much closer to 50/50 it might be less of an issue.
Mine is also about 56:44 or so, when I am doing a hard ride. When just tooling along, it goes as high as 59:41. I thought that is rather strange?
It's not that strange I think. On both Assioma Duo's and Powertap P1's I have about ~54-46 when doing easy to moderate power, and 50-50 at high power and sustained climbing (probably lower cadence in climbs is a factor too). Anyway, closer left-right match at higher efforts.

BTW the Assioma Duo's are flawless with me, would definitely recommend them. The P1's suffer from similar battery cap issues like the Vectors seem to do, the Assioma's have no such problem because of the fixed internal battery.
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TobinHatesYou
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Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

deepakvrao wrote:
Tue Apr 30, 2019 4:25 pm
RossLB wrote:
Tue Apr 30, 2019 2:41 am
It really depends on how far out your left/right balance is. Mine is about 54/46. If I used the left power meter on one bike and the right on another bike, they would be different by 16% (108% vs 92%), and both would be inaccurate by 8% but in different directions. This would be too unreliable for training purposes. But if you are much closer to 50/50 it might be less of an issue.
Mine is also about 56:44 or so, when I am doing a hard ride. When just tooling along, it goes as high as 59:41. I thought that is rather strange?

Nope, like I said earlier, L/R balance isn’t static. It depends on many variables per individual and it’s why single-sided PMs really aren’t that great. So you can spend $400 on a low-end 4iiii left-only crank or $650 on Assioma Duos...I know what I would choose.

sennder
Posts: 110
Joined: Mon Aug 08, 2016 12:13 pm

by sennder

I have had a great experience with the Favero Assioma Duos. Installed in seconds. No issues whatsoever. Work with every device I've tried. I only have a few gripes:
  • Clip in is pretty tight, though a trick I read on slowtwitch forum really helped with the problem. Not much tighter than my R8000 pedals anymore.
  • The transmission to my Wahoo Elemnt Bolt lags by a second or so. Not really an issue while riding in general but it's a bit bothersome during structured workouts on the fluid trainer.
  • Pods with constantly flashing lights are not the best aesthetic. I hardly notice them anymore though, and the lights are a reassurance that both pedals are on and transmitting.
I went with the Assiomas because of the relatively lower cost compared to other dual sided meters + ability to put them on any bike.

--Sennder

dim
Posts: 525
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Location: Cambridge UK

by dim

ome rodriguez wrote:
Tue Apr 30, 2019 9:16 am
Power spikes and drops even with the new battery covers. Also tried the cork inserts, was better but when the cork thins down then back to the same problem. The srm was ‘install and forget’
I have the same problem with my stages gen 2 powermeter, but I'm going to try Energizer 2032 batteries ...
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cdncyclist
Posts: 79
Joined: Wed Feb 17, 2016 12:10 am

by cdncyclist

dim wrote:
Tue Apr 30, 2019 8:34 pm
ome rodriguez wrote:
Tue Apr 30, 2019 9:16 am
Power spikes and drops even with the new battery covers. Also tried the cork inserts, was better but when the cork thins down then back to the same problem. The srm was ‘install and forget’
I have the same problem with my stages gen 2 powermeter, but I'm going to try Energizer 2032 batteries ...
Several issues appear to be conflated here. Just my opinion, but here is how I would prioritize:

1. Training with power >> training without power
2. Using a powermeter that works (accurate, precise) >> using a powermeter that doesn't
....
Yes, it's a short list, because I think many of the points brought up are what I would consider to be little things that depend on an individuals preference, context and circumstances ($, #bikes, how obsessive you are about specific metrics that have largely been unproven to improve performance, etc.) and anecdote that may not generalize (x powermeter is broken or frustrates me because it does y).

amngwlvs
Posts: 144
Joined: Fri Apr 20, 2018 2:45 pm
Location: Barrie, Ontario

by amngwlvs

OP reporting back in - I ended up ordering the Stages dual side crank based PM. At the end of the day, already having a couple of bikes with 105 and Ultegra pedals and a couple pairs of shoes with the corresponding cleats, switching to the Assioma's would have required buying at least one other set of Look pedals to prevent having to swap pedals everytime I want to swap bikes (one spends a lot of time on the trainer) which minimizes the price difference somewhat.

The TCR is at the shop now with the PM expected to come in today. I'll ride that as a dual side for now, get used to riding with power, check L/R balance, etc and can look at putting a left on one bike and the right on the other down the road. In the mean time I'll also swap the R8000 crankset off of the TCR and move it to the Propel.

Thanks for everyones advice and feed back!
2018 Giant TCR Advanced Pro 0 Disc
2015 Giant Propel Advanced 2
2013 Trek 520

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