Ergomo Validity shot down....

jbvcoaching

How did you measure that, and what were the results?

jbvcoaching

Just to elaborate on this one, inexpensive barbell plates (not certified for weightifting competition) can be off by enough to skew your test results. A more useful approach for cyclists can be to buy an accurate scale ("postal" scales come as low as $20), then just use any old combination of crap (water jugs, tools, etc) to rig up the exact weight you want.

The advantage of this is you can test your PM using different weights, even if you just buy the one tool. Plus, if you're a weight weenie (or if one of your cats has a weight problem and you need to weigh her regularly, not that that's why I bought one ) you can use the scale for all that as well.

yawg

John,

What's the minimum weight needed to get an accurate result?

TIA.

greg

JTE83

I was just guessing at these watt numbers. I do love low friction stuff like low friction hubs and BBs if they exist. Went ceramic for a few BBs and hub bearing but they still have friction...

jbvcoaching

Good question...I'm not really sure, but when I used to calibrate SRMs I tried to use weights from 10-50kg. The heavier setups required multiple people assisting.

I think Bob Tobin and Andy Coggan have some posts on the wattage list as to the range you'd want to use to verify a PT...perhaps R. Chung has an opinion?

Roadie_scum

Your guesses are wrong. Ceramic bearings are a waste of money in most applications. Not that they don't make a difference, but that the difference is not cost-effective because it is a very small order change for quite a bit of dollars.

Buy some nice wheels and a good set of tires and learn to tuck up on your bike. I just saved you about 100 times the watts. If you really want I'll sell you a bunch of small balls for $20 each as well.

ric_stern/RST

Not that I'm any of those mentioned, but i've used masses of ~5 to ~25 kg. I always used multiple masses and multiple positions on both sides of the cranks.

Ric

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beerco

I would say you'd want a weights which would give you equivalent peak and average torque to riding at threshold in a common gear at your standard cadence. You could then shift gears to get a couple more data points above and below.

RChung

Perhaps? Dude, I try never to let the absence of information restrict the breadth of my opinions (just the forcefulness with which I defend them).

I do something closely related to what Andy Birko suggested, but I looked at the actual torque distribution. I don't try to mimic the peak torque -- 80th percentile was good enough, and I can get that with a 20kg load. I check linearity by using the same 20kg load over several different gear ratios.

Speedskater

So, I´m back from the Eurobike trade show, where I had the opportunity to speak to the head of service of Ergomo. He was not aware of the publication mentioned by the OP, but when I confronted him with the results, we had a good discussion. First he insisted that it is questionable that the the SRM is accepted to be absolutely precise, just because its on the market for 20 years. Second he said, they has bikes with SRM, PT and Ergomo installed and SRM and Ergomo are showing the same values. The same is true for the Ergomo and a Cyclus ergometer (This ergometer was designed in the ex-GDR and is accepted to be very precise). But he also responded to the left-leg-question. When three riders are riding the same wattage on a Cyclus ergometer, the wattage measured by the Ergomo can differ by as much as 10 W from person to person. More than by leg force inequalities this is based on pedalling technique, i.e. how much the leg on the upstroke pushes against the other one. He said this still was within the claimed accuracy of the system. Regarding the publication he questioned whether the system was installed properly, since it´s not that easy, as he admitted. Ergomo is working on an installation that is less prone to mistakes than currently.

The Ergoracer 3 software that should be downloadable for one week now, is shipped with all new systems. They did not put it on the download section since they wanted some feedback first. I got one on CD, so if there is some interest, I can put it online as torrent file.

Roadie_scum

Absolutely not. No. The SRM is not accepted to be 'absolutely precise' by any right thinking person. It is accepted that it has a low error (particularly in the science version used in the study). This is not 'just because its on the market for 20 years', but rather because it has been validated over and over in a number of scientific studies. Powertap has also been subject to some of these studies and passed well. For Powertap there has been a question identified in the literature of small variations in very high wattage situations depending on gear selection/cross-chaining. It's very minor though, not at all like the wild fluctuations the Ergomo had in the study.

Ergomo falls down at the first hurdle.

Speedskater

At their booth they had a Cyclus ergometer with a Ergomo mounted and you could compare the values. In all situations the values were comparable. As the head of service pointed out, PT and to a lesser degree SRM are fool proof regarding installation, while Ergomo is not. So in a "real" test, one should compare a Ergomo installed by Ergomo with a SRM and then one could really draw conclusions. Until then, this study seems to be guesswork to me. Of course, they got these results, that I do not doubt. What I do doubt is the basis this values originate from (i.e. installation).

BTW, Ergomo mentioned that different torque when a SRM crank is mounted on the BB results in a different offset. Has anyone seen this on his SRM?

Roadie_scum

If Ergomo need to install my Ergomo and the entire AIS can't work it out (which they couldn't - at least they couldn't make it accurate) and a bunch of French scientists can't work it out, I'm not trusting myself to do it, or my LBS, or pretty much anyone else for that matter.

Speedskater

How does being a scientist qualify to install a BB? What´s AIS; Australian Institute of Sports? If yes, do you have a link to their test.

I agree, that the installation is an PITA and really hope that Ergomo will succeed in their atempt to make the installation easier. But I think that readers of this forum might know more about correct installation than most scientist and all points about installation discussed n this forum were confirmed by Ergomo to be relevant.