New powermeter rumours

Discuss light weight issues concerning road bikes & parts.
User avatar
Posts: 737
Joined: Fri Nov 14, 2008 4:55 am

by itsacarr

Having been an SRM user for almost 5 years and having some garmins lying around the PC8 is basically everything I could have wanted from the previous two generations and a bit more. Pretty excited and very curious to see what type of aplications they wind up with - how easy it is to upload wireless to something like tpeaks or srm's software and definitely how soon they will impliment the rechargeable SRM's.

Well done.

Posts: 96
Joined: Fri Jun 01, 2012 11:45 am
Location: Bristol, UK

by DrGalactus

PC8 Update from DCR
1) The PC8 will indeed allow for all ANT+ power meters.
2) SRM will be implementing left/right balance metrics, including Torque Effectiveness and Pedal Smoothness
3) As previously noted, the Bluetooth 4.0 will be utilized for data transfers, and not sensors (including BLE HR straps)
4) The PC8 will allow workouts to be added to it and executed on it
5) The PC8 will have customizable training zones by power/HR/Critical Power/FTP
6) The PC8 will include the TrainingPeaks metrics of Normalized Power (NP), Training Stress Score (TSS), and Intensity Factor (IF)
7) They are targeting May 2014, as opposed to “Summer 2014” as previously communicated

“The comment from Sebastian Raebiger about SRM seeing no value in left/right pedal, primarily comes from the small amount of peer reviewed research being done on training prescription (based on single leg workouts to improve ‘balance’ or performance). SRM has been working on a torque analysis system for the last 10 years, and have begun to see its successful application for bike fitting and positioning. Adding this feature to the PC8 will allow us to take that application outdoors. “ ... tml#update

by Weenie

User avatar
Posts: 7926
Joined: Wed Sep 26, 2007 1:57 pm
Location: San Francisco, CA

by djconnel

DC Rainmaker just published his extended Garmin Vector review

He gave me a pile of data and asked me to make some plots for him. I picked two rides from his pile and ran some numbers. I think this plot is a fairly useful comparison:


That's pretty freakin' good tracking by Vector, Quarq, and Powertap, especially considering there's expected to be a power drop by the time the power reaches the Powertap. Stages is deviant, but that's expected since it measures just one leg.

Posts: 826
Joined: Mon Apr 03, 2006 8:53 am

by uraqt

@ djconnel

Thanks for helping DC Rainmaker with your graphs, they really help present the facts : )


PS your blog is great too!!! Keep up the great data analysis !!!

Posts: 96
Joined: Tue Aug 24, 2010 11:53 pm

by drewb


Was this a truly random selection of 2 rides that you analyzed or 2 that showed the deficiencies of Stages?

For science sake I hope it was random selection and that you will follow up with enough other rides to make it statistically valid.

Thanks for your work.

Posts: 97
Joined: Sat Jul 09, 2011 5:01 am

by rchung

Drew, I think you may be unclear on what "for science's sake" means. What's important in these comparisons from the scientific point of view isn't how close two power meters are on average, what's important is understanding the conditions under which they differ and by how much. Plenty of science is done with non-random samples (for example, controlled experiments are almost never "random") as long as the purpose isn't to identify mean differences in "the wild." Wind tunnel tests of drag at non-zero yaw are done at specified yaw angles instead of setting the balance table at a random angle. Your concern about randomness in this case is misplaced.

User avatar
Posts: 2035
Joined: Sat Aug 29, 2009 4:30 pm

by Rick

At one time there was a big discussion here about whether there were "significant" differences between the ouput power of the two legs, and whether it should be measured. Does the big discrepancy of the Stages power meter (one side only) influence that ?

And I am surprised that Stages doesn't just go ahead and make a version that mounts on both crankarms to eliminate that discrepancy.

Posts: 96
Joined: Tue Aug 24, 2010 11:53 pm

by drewb

Robert, thanks for the response. I understand there were differences between readings on the above charts - with stages reporting different power than the other two. No problems with that.

However, I could live with those differences if Stages reported the same results as the others with 98 of the rides and differed in only 2 of the files.

What I wanted to know was if the above differences were a representative of a sample of rides or were outliers. Clarifying that would be better journalism if not better science as well.


Posts: 97
Joined: Sat Jul 09, 2011 5:01 am

by rchung

Drew, I'm confused about your confusion. The analysis shows that maximal power at short durations can differ across power meters -- in this case, the Stages differs from the other power meters tested. Whether that applies to 2 percent or 98 percent of your rides depends on you, not on Ray Maker, so what good would it do to know what his power-by-duration distribution is? There is no failure of either science or journalism here.

In Ray Maker's initial review of the Stages from last January, we identified a problem with the Stages at low cadence and high force. We didn't need hundreds of rides taken in all conditions in order to identify that problem. Stages initially denied that it had a problem and accused us of faulty science and analysis but they quickly updated their firmware expressly to deal with low cadence high force situations. Science works, and the Stages is a better product than it would have been if they hadn't released that update. (As it happens, the Stages unit that Ray was using to collect these latest data has been updated to current firmware, so remaining anomalies aren't due to obsolete firmware versions).

Posts: 600
Joined: Mon Jan 02, 2006 7:10 pm

by ghisallo2003

Have the Xpedo power pedals reported on Pez been mentioned here before. Image

If they work, they do appear a bit less ugly than the Garmin pedal pods.

Posts: 182
Joined: Tue Nov 24, 2009 10:26 pm

by asv

Looking at most of the other data, the stages tracks very well. Your guys little internet war against stages is quite comical.

Posts: 1917
Joined: Thu May 01, 2008 8:51 pm
Location: France

by maquisard

Stages works well if you have good left-right power symmetry. If you don't then it will not 'track' very well.

Asymmetry is the norm, not the other way around.

Posts: 1170
Joined: Sun May 16, 2010 7:28 pm

by kulivontot

maquisard wrote:
Asymmetry is the norm, not the other way around.

Prove it.

User avatar
Posts: 3762
Joined: Fri Sep 15, 2006 6:02 am
Location: On the bike

by 53x12

Prove it? It is well understood there is asymetrical length strength. That is well documented with studies.

The issue is what to do with this data? Is asymwtrical length strength good? Bad? Abnormal? Will fixing it decrease injuries? We don't know yet. But Vector will hopefully help answer those questions and others.
"Marginal gains are the only gains when all that's left to gain is in the margins."

by Weenie

Posts: 97
Joined: Sat Jul 09, 2011 5:01 am

by rchung

kulivontot wrote:
maquisard wrote:
Asymmetry is the norm, not the other way around.

Prove it.


"For many years, mainly to simplify data analysis, scientists assumed that during a gait, the lower limbs moved symmetrically. However, even a cursory survey of the more recent literature reveals that the human walk is symmetrical only in some aspects."

"H:q ratios and bilateral leg strength in college field and court sports players" found significant bilateral differences according to type of sport and leg dominance.

"...the findings of the current study suggest an association between knee strength imbalances and the joint angle, as well as the torque produced in single-leg jumps, although no relationship between knee strength and jump height was observed."

" Statistically significant differences were recorded between the most and less efficient leg in strength and power performances for both genders."

" EMG variability was asymmetric and appears to be strongly influenced by exercise intensity for cyclists and non-cyclists, especially during sub-maximal intensity."

"During cycling, bilateral differences are frequently found and vary with the competitive situation, pedaling cadence, exercise intensity and exercise duration. Regardless of the variability of asymmetry index between subjects, few suggestions are available to overcome lateral differences. Most of the research suggests that bilateral pedaling asymmetries decrease as the workload increases, however the relationship to injury risk was not clearly addressed."

There are lots more. Do a pubmed search.

Post Reply
  • Similar Topics
    Last post