Ergomo Validity shot down....

Originally Posted by Roadie_scum

Yeah I believe the scientists... if you want to check on their methods look up the paper. I did. They used the science SRM with 20 strain gauges.



Because it is completely impossible to ride both of these at the same time? Or because they both very accurately read zero when you aren't riding them?

I *hate* it when I realise that I wasted my money.

Originally Posted by jbvcoaching

Mainly because you're not going to have that particular piece of equipment forever. So in the future, when you reinstall your Ergomo, get a new one, or get a different powermeter, it will be very challenging (if not impossible) to compare data from different seasons. The benefit of a powermeter that's accurate is, you just keep using accurate powermeters, and you can fully utilize all your historical data without caveats.

For example, there's a guy on the wattage list right now who was using an uncalibrated SRM amateur in 1999, it told him he did 423W for a ~20 minute TT back then. It's only 8 years later, but his current SRM Dura Ace (also uncalibrated) is telling him he's producing around 25% less power for that duration now.

If he believes these numbers, then it drives him to perhaps train (and view himself) differently than if he calibrates the current SRM, and accepts that he'll never know how many "real" watts he did back in 1999.

Longer term data analysis is one of the biggest values in using a powermeter, using an inaccurate PM really negates that value.

Besides that, the Ergomo isn't even consistent (with itself) due to the R/L balance issue. One of my clients owns an Ergomo, a PT, and an iBike. We know through a variety of tests that he has a cadence-related L/R imbalance. He's right leg dominant at lower (under 90) cadences, left leg dominant at higher cadences (over 100). So his TT data looks different than (for example) his crit data depending on which PM he's on, even though everything works for overall load because he's got them fairly consistent with each other. Unfortunately, every time we test or see a new high power, we have to go through the extra steps of asking "which powermeter" and qualifying it. Kind of a PITA.

Small (5% or less) differences like this also make it tough to use the PM for assessing small gains in fitness, or for aero testing (if that's something you're into).

So if you're only going to use this particular Ergomo, and you're going to use it on the same installation for as long as you race and train with a PM, and you don't care about long term data analysis, aero testing, or measuring small changes in power for different durations, then you probably have nothing to worry about. That then kind of begs the question, exactly what are you using a powermeter for, and can you use a watch, PE, and a local climb for the same thing?

Originally Posted by PaulMD

I haven't read anything about calibration of a powertap. After reading this story: can I calibrate my powertap, and how often should it be done?

Originally Posted by Roadie_scum

Yeah I believe the scientists... if you want to check on their methods look up the paper. I did. They used the science SRM with 20 strain gauges.



Because it is completely impossible to ride both of these at the same time? Or because they both very accurately read zero when you aren't riding them?

I *hate* it when I realise that I wasted my money.

Originally Posted by POGATA

Where??

Originally Posted by Roadie_scum

Originally Posted by doctorb

Gentlemen,

Having just read the 2 page published report, Ergomo's validity has not been shot down.

If one assumes the SRM is correct (and that is quite an assumption), in several cases the Powertap's deviation from the SRM is greater than the Ergomo's.

To quote the paper, "ERGOMO overestimated the PO by 5% compared to the SRM." "POWERTAP underestimated the PO by 6% compared to the SRM."

From a scientific perspective, more than one version of each meter should be tested to determine reproducibility. I personally would have liked to see the test run on a Computrainer for an additional comparison.

I have no bias as I use both the Powertap 2.4 and the Ergomo.

Barry

Originally Posted by POGATA

I have an Ergomo Pro and a SRM Dura-Ace, why have I not noticed the difference in the power numbers between the two?

Originally Posted by yawg

What is your procedure for the stomp test?

Originally Posted by RChung

The classic description is here: http://www.midweekclub.ca/powerFAQ.htm#Q23

However, I would slightly amend that procedure. It's kinda hard to balance on a pedal while the crank is exactly horizontal, so this is what I do:

1. Use a known weight (like barbell plates).
2. Clamp the bike into a trainer but back off the roller pressure so the rear wheel turns freely. Hang the weights from one of the pedals. Place the PT into torque measuring mode. Backup the rear wheel very slowly until the torque reaches a maximum. That will occur when the crank is horizontal.
3. To check linearity, repeat for a couple of different cogs. Doing it this way is easier than changing the weights for the same cog.

Originally Posted by JTE83

Shouldn't the ergomo read higher watts than an SRM because it accounts for power lost in the BB itself whereas the SRM measures the strain / calculates the power between the Chain and the crankarm thus BB loss is not measured by the SRM?