If the zero offset of the SRM has changed by an appreciable amount over the last 6-months, then I would be asking when was the last time the battery was changed/calibration updated on the SRM? If the battery in the SRM is less than 1-year old and you have a Garmin that can update the slope in your SRM, then my suggestion would be to re-calibrate your SRM (alternate link to calibration procedure).

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¯\_(ツ)_/¯

Thanks! So you mean the P2M could be more precise as the SRM is running low on batt ?

I had batteries changed and everything updated on the SRM back in early 2015. Done in SRM Germany and they did a slight update on the slope back then.

I think I can update the slope on the SRM via the SRM software too ...

Thanks a lot

Tom

Well, Osymetric claims to increase power by 5% to 10%... Most people credit at least the vast majority - if not all - of this increase to the way crank based pm get their readings... So it could be a real gain or it could be only a matter of different readings.

Hence maybe you should consider the same setup but for having Osymetrics in and out. I.e., in the same bike (say your TT bike), with the same PM. Then use a trainer which reads power to make a comparison of the 2 systems (with and without Osymetric). Since you will be reading at the rear wheel (technically on the trainer) you will be able to tell if Osymetric is the one to blame for the different readings, which would be in fact great news for you (and for those who use it)...

Hope it helps.

Cheers,
Raul

Thats a good point indeed Raulmf - thanks for that view!

One other thought is what about the difference in TT/Tri versus road positioning? Wouldn't the chainrings on the TT/Tri bike coupled with the difference in position/setup afford a different power output as well?

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Both setups and "tests" are done on the same climb, so not in aero position, but on the "hoods" of both bikes.

If anything, I would have guessed my roadbike (better position to push more watts) with the SRM would render the highest output then ...

Thanks anyhow for the input!

Tom

Different positions could mean different adaptations.

If it was a steep climb, your time split over that distance should tell if both power meters are reading the same, assuming your bikes are the same weight, or you just have to normalize the data for that difference.

RPE isn't really a good gauge to compare power readouts unless you swapped both bikes back and forth during the same workout. RPE varies a lot one day to the next. When I'm well rested, 110% feels like 90% for the first 2 minutes at least until my breathing rate picks up and I can tell I'm above threshold.

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TrainingBible Coaching
http://www.trainingbible.com

The Power2Max will inflate numbers when using Osymetric rings. I know they say it won't, but that's not my experience. There's also no evidence that Osymetric rings increase your power output.

I have a Powerbeam Pro and a P2M. I have recorded both several times out of curiosity. While I know they measure in different spots on the bike and should have different readings, they average only a 2-4 watts difference every time I'm using round rings. That's been about a 1-2% difference when comparing specific intervals at least 10 minutes long, with the P2m being 1-2% higher....as it should be in a clean, high-end drivetrain.. I don't bother changing settings when using a bike without a power meter on the trainer, which is really nice.

Now, the couple (not enough to be significant) rides I have done with Osymetric rings, the P2M consistently reads ~5% higher than the Powerbeam Pro.

Nothing is wrong with either device. I'm a mega fan of Cycleops and Power2Max.

I've used Power2Max with Q Rings and Powertap P1 pedals. They both showed values within 2-4W from each other at on intervals ranging from 230-350W. This was no scientific test or anything but it seemed to me that P2M does not inflate #s with oval rings... but then again P1s maybe inflate them too.

P2M and P1 pedals? Belt and suspenders kinda guy?

I should have noted my only experience was with Oysmetric rings. It's been consistent between multiple rides that the Osy rings measured slightly higher at the P2M than PBP vs. when using round rings. I haven't seen too many power meter companies saying their stuff doesn't work with non-round rings.

I'm not too invested in who is right, just noting my experience. They were all done with the same bike, trainer, wheel, crank/PM, on PBP's ERG mode for long-enough steady intervals with one device recording the P2M as a PM and another recording the PBP as a PM.

Had to try it :) Ended up keeping the pedals and selling the P2M and Q Rings.

Check this article out. It may help explain why you're seeing an increase in power after you've installed the osymetric chain rings.

Thank you!

For the life of me, I couldn't remember where I had it in my head that there was a ~4% inflation and my (limited) testing agreed with that.

No problem...just get a high quality weight of known mass and perform a static torque calibration. Oh wait...

Even though you can't change the Power2max torque slope you can still check to see if it matches what the factory claims it is. Do the SRM too while you're at it.

Hugh

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Genetics load the gun, lifestyle pulls the trigger.

Thanks for a lot of quality input here.

What if I took a more practical approach, setting up this test to ride on both bikes:

10 mins climbing the same climb (start from same point on both bikes) at 6-7% at the same 300 watts.
That should take me some 2.5 km up the climb and if there really is a 6% difference, this would mean mean 150m in difference of the distance climbed.

Could that work ? Not very scientific I know...

Tom

Probably be more like 35m

Not sure I understand why 35m ?

It certainly would be a lot better than just wondering and if done with calm conditions, zeroed zero offsets and even efforts should give you a pretty darn good check on how the two stack up. Sounds like fun too.

Hugh

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Genetics load the gun, lifestyle pulls the trigger.

Why don't you just test them both on a computrainer at a local lab?

Because speed scales exponentially with power and not linearly