Power Meters / Powermeters (SRM, Powertap, Quarq, Ergomo, Vector, Stages, power2max, P2M, 4iii, InPower, Cinch)

I've finally entered the smart trainer world. I have a bunch of powermeters on different bikes and they can be scaled i.e. a set offset. Given that some PM's seem to read 'high' or 'low', I'm going to actually try testing this using the Kickr as a ref point.

Anyone tried this and have a view on protocol to use? I plan to try a series of intervals around where I usually train, focusing on threshold where my winter is going to unfortunately be based. Any suggestions welcome.

Check out DC Rainmakers comparison tool. Although I'm sure you already have it in mind.

I had initially dismissed as I'm not testing absolute accuracy, but actually yeah it's a good shout to compare to the Kickr baseline.

can I ask what the point of this testing would be? it's not like you're able to adjust the calibration yourself so even if you discover the envelop for accuracy across your PMs it's not going to effect your training much.

just seems like a bunch of bother for not much reward, other than the joy of planning / doing / knowing.

You can adjust the offset on the units, so if I find that there's a consistent difference in theory they will be closer together. And as you know when trying to ride say a threshold interval that's 5% higher than expected, it's not much fun (but good training blah blah)

Easiest thing is just to do a ramp test, 3min blocks at 25w increments on each power meter (using the Kickr's power as your reference). Then you can check offset as well as slope.

Would you record one on say trainer road and one through your head unit?

FFS Powertap G3 needs 61802-2RS, it's only the drive side that uses the 6902 bearing.

Annoyingly, now that I know that and can search my emails I can see the fucking service details from a previous G3 hub:

700.PTSP18219 - P/Tap Svc Part Bearing,6902-2RU,28X15X7mm £6.00each. Qty:3
700.PTSP18221 - P/Tap Svc Part Bearing,6802-2RU,24X15X5mm £5.00each. Qty:1

Yeah that would work okay as long as you can download the file off trainerroad to compare. Or just use two Garmins

Powertap hub, is there a guide to what number should pop up when I calibrate? Selling it on as changing to something more versatile / I can use with any wheels, but want to check it's not fubarred first

Which model Powertap hub?

512 +-12 for the G3 hubs.

I think you just zeroed the SL+ but then I have memories of seeing 1000s but maybe that's when they're borked.

Cheers, it's a G3

I think you just zeroed the SL+ but then I have memories of seeing 1000s but maybe that's when they're borked.

Nah, early ones give you the serial number, so it's the same very time. Pro and G3 onwards give you a calibration number.

Nah, I think that's only on Garmins. If you have the (Little Yellow Computer) LYC it shows you a torque value somewhere. I haven't used any of my LYCs for maybe 5+ years but I'm pretty sure if you click deep enough into their silly menus you get a torque number.

ie. "Recently I have been trying to reset my torque via the LYC (Little Yellow Computer) and it never works. I follow the directions to a "T" and it just constantly flashes (the word "watts"), but the number never goes to zero. It constantly shows between 20-22, but won't reset."

https://forum.slowtwitch.com/forum/Slowtwitch_Forums_C1/Triathlon_Forum_F1/Powertap_LYC/Can%27t_Zero_my_Torque_P3367165/

I had a few fail in a row (because Paligap never waterproofed them properly) and I remember doing something to test them and if it was out of range it would be another warranty Paligap service for me.

http://thecyclingaddiction.blogspot.com/2010/05/powertap-torque-test-rough-initial-test.html

Yep, my Joule GPS does the same. But only weirdos have Cyclops/Powertap head units.

I agree.

https://www.youtube.com/watch?v=eoXb79SpVtc

Flibble.

Ah balls, new batteries in and it gives 540

That sounds close to where it should be? Is this before or after doing a Calibrate?

After, yeah isn't far away and is consistent

You could do a weighted pedal test and see if it's too far off.
Do you have other PMs? I ask because, if it's off but consistent, it's only really an issue if you have more than one meter and want them to be close. Oh and you don't want to be decimated after bragging about your 460W threshold only to get your PM repaired and finding this drop to 260W :)

Getting a 4iiii so I can use same power meter indoors and out, so could compare. If there's a big discrepancy it could just mean my right leg is an absolute monster (or twiglet)

I'm getting rid of a 6800 Chainset, 170mm 52/36 including a stages powermeter if anyone fancies it? Will come with the non-power left hand crank and I can throw in a BSA threaded BB for it too. £275?

Powermeter is brill and has never missed a beat. I've just stuck a new battery in it, so good for a good while.

I have a Rotor 3D 30mm axle crankset with a four arm/Shimano P2M spider- currently with 52/39 Ultegra rings. I may have a spare, new BSA adapter BB as well but no promises on that. Any interest?