Road Bike Racing - Fun facts about SRM

So my friend has SRM and we were discussing zero offset and what happens if you reset it during the ride. I was saying it uses the latest one, my friend was of the opinion it will use multiple ones. So if you set it in the beginning then half way, it will use the first one for first half and second for second half. This is what folks at SRM have to say about it. I was right. :)
Only one zero offset can be applied to the entire file. A zero offset change
of 10 Hz would be about 1 watt.

The only thing you can do would be to break the ride into two parts by
hitting the pro and set button then begin a new file, then you can have a
new zero offset.

What you may want to do is to reset the zero offset in the middle of the
ride and just apply this to the whole ride. The change in Power is probably
very small due to the difference.
Leslie

I see now reason to doing a zero offset during a ride. I know that can be beneficial in extreme weather fluctuations but I may be missing the reason behind multiple zero offsets.

I will do a second zero offset if the wattages are not looking right, if I drop the chain (which may knock the power sensor slightly), with extreme temp fluctuations (as can occur over a long ride or one with monsterous climbs), or if I jump into a ride ater having JUST brought the bike out from the indoors (Air conditioned Temps to in-th-sun temps can be quite a bit different and may need a few minutes to adjust). Does anyone pick a specific gear combo to do the zero offset in (as it oes vary slightly if there is cross chaining)?

I see now reason to doing a zero offset during a ride. I know that can be beneficial in extreme weather fluctuations but I may be missing the reason behind multiple zero offsets.
So lets say you leave when it's cold, when it gets hot you resest zero offset. Since it's using only latest one, once you download the data morning data will be slightly off.

How much can the temp change during a ride where you live?

How much can the temp change during a ride where you live?
Depends... If I leave early in the morning I can go from needing arm warmers to wishing my jersey had cooling. Usually around the bay it's cooler, then once you go on the other side of Mount Hamilton it gets really hot.

For me, (I have the carbon FSA cranks), I set my bike outside for the twenty to thirty minutes it takes me to get ready. By then if there is any significant difference between the garage temp and the outside temp the bike should be ready.

My Ergomo also requires calibration as temperature can affect the strain gauges, but I can re-calibrate mid-ride and it'll use the new value from that point forward. Guess that's an advantage of ergomo over SRM.

and that might be about it... ;)

and that might be about it... ;)

I was thinking that as I made my post, but I didn't want to say it.

My Ergomo also requires calibration as temperature can affect the strain gauges, but I can re-calibrate mid-ride and it'll use the new value from that point forward. Guess that's an advantage of ergomo over SRM.

I thought Ergomo used laser measurement of deflection; not what I use as a definition of a 'strain gauge'. Am I wrong, or do we have different definitions?

I thought Ergomo used laser measurement of deflection; not what I use as a definition of a 'strain gauge'. Am I wrong, or do we have different definitions?

no no, you're right. i was super tired when I made that post.

My Ergomo also requires calibration as temperature can affect the strain gauges, but I can re-calibrate mid-ride and it'll use the new value from that point forward. Guess that's an advantage of ergomo over SRM.

An SRM with a drifting zero offset would still be far more accurate.

An SRM with a drifting zero offset would still be far more accurate.

Precision > Accuracy for me.

Precision > Accuracy for me.

Ergomo's precision is terrible, too.

Ergomo's precision is terrible, too.

Well, if you want to step up and buy me an SRM, I'd gladly trade in my Ergomo. Until such time, step off.

Hey guys chill. This post was never intended to be turned in to which Powermeter is better. Just to clarify some things I read on here and heard from my friend.

ok. but for the record, iBike is better.

There has been a lot of discussion about the Ergomo. Here are some of the most relevant and interesting tidbits:

http://groups.google.com/group/wattage/browse_frm/thread/b69b7377c39c5147/5f44429821ce386f?lnk=gst&q=ergomo&rnum=1&hl=en#5f44429821ce386f


The only other factor I have noticed is that if I turn the cranks over
while coasting - the Ergomo will often read 30-50w while the PT shows
zero.

http://groups.google.com/group/wattage/browse_frm/thread/ea96e36a6baa7d85/0ca3b353def0fd1a?lnk=gst&q=ergomo&rnum=7&hl=en#


My own gut feel is that the Ergomo over reports power at lower levels
(as I have observed when testing - 60-90w at absolute zero output but
pedals turning) and so as the K factor is adjusted downwards to cater
for this, so the higher power levels begin to under report.

http://biketechreview.com/phpBB2/viewtopic.php?t=1124&highlight=ergomo&sid=80d551c98935791affcc1d2472557385


summary of this post: don't buy one

There are several threads over on slowtwitch about the Ergomo system - mostly people who have never cross-checked them against another PM saying how great they are. I have repeatedly challenged those users (including several high-profile shops that sponsor pro triathletes, who claim that the Ergomo was within 1% of their SRM Science) to provide me (or anybody else) with power files or some other form of data proving its accuracy - in return there has been deafening silence.

I recently had a chance to ride an Ergomo for 4 weeks and compared it with my PT SL. The shop I work at is an Ergomo dealer so I've had plenty of practice installing the units and I know mine was installed exactly to spec. To make a long story short, it is not accurate enough. In intervals as long as 5 minutes the accuracy of the Ergomo was never better than 6% - in my opinion this is far outside of the range of resolution required for effective use of a power meter in training.

The reason is fairly straightforward: it measures only the power produced by your left leg and doubles that number. Because humans are not machines the power distribution between legs is inherently inequal - it ranges from person to person - some are as close as 1-2% while Hunter told me he has seen people with up to 20% (crazy!). Personally I was around 8%. This overall difference in leg power will affect the Ergomo power reading up or down relative to an SRM or PowerTap - if your right leg is stronger it will read low, if the left leg is stronger it will read high.

However more important than just the overall leg power discrepancy are the instantaneous variations in leg power discrepancy - for example my left leg is not always putting out 8% more power than my left, it probably varies a few percentage points around that average. This instantaneous variation seems to average out over longer periods of time but for shorter durations (which are arguably the most important in training with PM) it renders the PM practically useless.

Ergomo USA will say one of the two following things when confronted with the inadequacies of their system:
1. It was probably not installed correctly (even though it was...)
2. Your individual leg power discrepancy is just throwing the numbers off -i.e. it is just something about you, this works for most people, just not YOU. (this just simply isn't true, and the complete lack of data supporting this position and mountain of evidence to the contrary is most telling.)

while my mind is 99% made up on this issue, I'd still be interested in seeing anyone's files showing any apparent agreement between an Ergomo and another recently-calibrated power meter of 2% accuracy or better.

Coggan had this to say about his early experience with the Ergomo:

http://forum.slowtwitch.com/gforum.cgi?post=1075976


I was beta testing an Ergomo Pro, and I concluded that I was going to stick with my SRM and my (my wife's, actually) PowerTap.

Sure: the data that I was getting from the Ergomo weren't up to my standards for accuracy and precision.

And lastly, about precision vs. accuracy in this context, Coggan has this to say:

http://forum.slowtwitch.com/gforum.cgi?post=1190412



I'd say (and have repeatedly said) that this is a false hope.

First, you're assuming that somebody is always going to be using the same powermeter, and will never have to replace it if it breaks, wears out, gets stolen, is made obsolete by something newer/better, etc. Since that is unlikely, you want a powermeter that is not only very precise, but also very accurate, or else you're going to have to deal with the uncertainty created when you get a new powermeter (e.g., for another bike) that reads higher or lower than the original.

Second, while accuracy and precision are in theory two different things, in reality they often are not, at least when it comes to electronic instrumentation. That is, a well-designed and well-manufactured product will tend to be both accurate and precise, whereas one that is poorly-designed and/or poorly-manufactured will tend to be neither.

P.S. The iBike might actually yield as good data as an Ergomo.

I've used the Ergomo with my PowerTap and found the numbers to be accurate and precise. End of discussion.

Judging by your emotional outburst earlier, it appears you're really motivated to justify your purchase. After all, it would be hard to admit you sold a better powermeter and bought a more expensive but inferior one. And to remedy that situation would require even more expense.

What's even sadder is that all the information is out there and you still made the wrong decision.

Why don't you post some files of your PT and Ergomo running concurrently?

The preponderance of evidence indicates that the Ergomo is neither accurate nor precise.

MMM...this could be entertaining.