I just received a set of Favero Assioma PRO RS-2 pedals. I also have a set of Specialized Dual Power Cranks, which are essentially 4iiii, I believe. I’d like to validate the cranks against the pedals. Does anyone have any hints on how I could record on both simultaneously?
and then compare the data?
Really the only way to do it is to have two GPS units on the bike.
My question for you though is, what good will it do? to the best of my knowledge, there is nothing you can do to change them once you “validate” them. My suggestion is to just ride and accept the numbers that you get.
“My question for you though is, what good will it do?”
I did a few rides with one Garmin recording from my SRM crank and another from Wahoo Speedplay power pedals. It quickly became obvious just by comparing average power over Strava segments that the Speedplay pedals were significantly off (~10%). I sent the data to Wahoo and they replaced the pedals under warranty.
Record on two different devices and then head over to Gpllama’s favorite site on the internet, the dcrainmaker analyzer tool.
I believe dcrainmaker has analysing software you can use for this.
I once tried this, used 2 cycle computers then loaded the files to Golden Cheetah, from there exported a second by second dump of the time and power readings and compared in Excel.
I’m sure the DC Rainmaker software would have been easier but you’d need to pay for that.
If you’ve got a Garmin and an intervals .ICU account, there is a Garmin App that records s second power meter via Ant+. You can then get a trace of both on intervals to compare them.
Both the Assiomas and the 4iiii metres have a setting that allows you to increase or decrease the reported power in order that you can align different power meters more closely
Hmm, this isn’t helping with my “but I just want to use a single head unit!” first world problem here. I have an older head unit I can pull out for purposes of this, so that should in theory solve that problem. And I have a little time to figure this out… I live near Washington DC, and I’m not going to be doing any outdoor riding for a bit. As for the why, it’s mainly to see if my (perceived) recently wonky left/right balance on my Power Cranks are due to an issue with the cranks or an issue with me suddenly developing an imbalance. The Favero’s have a really good reputation for providing accurate information, so I’m planning on making them the baseline. If they are showing close to the Power Cranks, then I’ll posit that the problem is me and I need to strengthen my left side. If they are showing that I’m actually not that imbalanced, I’ll pull the cranks and get them calibrated by 4iiii (if they do that even). Of course, these cranks are 6 years old and not even manufactured anymore, so it may be a moot point.
You could always use a phone plus a any exercise recording app as the second head unit.
(I used to use the Wahoo app for this, until I noticed that it always sets the crank length to 172.5 mm…)
I’d just use the pedals, a known good quality reference point and simplify your aim, otherwise you could be chasing something that’s not there. If GPLama says they’re good, then they’re good.
If you have a Garmin Edge, the Connect IQ data field Ant+ Power Meter allows pairing and recording a second power meter: Connect IQ Store | Watch Faces and Apps | Garmin
Zwift power has an easy to use comparison tool, can use whether your on zwift or not
Indeed, I used that data field a long time ago to do it once. My main issue was long-term it was sorta a pain in the butt to keep pairing to different power meter units, but, perhaps there are changes there.
As someone else noted, if I need to record multiple sensors I typically will juse use extra watches/bike computers. But in a pinch, my favorite app is just the free Wahoo Fitness app. They’ve got really good data export options there, and it makes it super easy to get the files into a .FIT file afterwards for comparison.
That said, it’s been a long-time since someone asked a question about Power Cranks, but a tiny bird in the back of my brain rememers discussions from years past that basically the Power Cranks pretty much break many of the algorithms of downstream data (e.g. pedals), since the rotation element isn’t exactly even. Whereas things that measure power before it (e.g. spiders) were fine. Again, way-back bits in my head.
By coincidence, I have tested my Favero Assioma Pro RS-2 numerous times against against the S-Works Power Cranks on my Tarmac SL6, and they are astonishingly similar, almost identical. In contract, my Garmin RS200s consistently report 5-10 watts lower. I take this as evidence that the Assiomas and Power Cranks are very accurate, whereas the Rallys are less accurate. I didn’t expect the Power Cranks to be that accurate, but I remember Specialized made a big deal of their special laboratory calibration process back when it was released.
Based on all this, I think the easiest solution will be to record one of them on my watch (Garmin Forerunner) and the other on my head unit (Garmin 840). The good news is that after weeks of cold, we are getting a little relief here in DC… the rain is currently washing all the salt off the road as well!. So I may finally be able to ride outside for the first time this year.
Also, for @Torbjorn , I think it’s awesome you’re riding an SL6 with those cranks as well. If you’re also running mechanical Dura Ace with rim brakes, you clearly have some pretty refined taste!
Have they fixed the crank length thing in the Wahoo app though? A couple of years ago, I used it happily for dual recording Zwift and/or RGT races for months until I noticed that something had changed the crank length for my Assiomata to 172.5 mm (which I didn’t have on any bike back then) and a bit of investigation made me realize it was the Wahoo app, and it would happen again every time I connected the pedals to the app. There was no setting in the app itself to change this, either. (Of course the main reason it took me so long to notice was that the dual records were close enough either way…)
I have not tried the Wahoo app, but I have to set mine back to 170mm every time I calibrate them with the Favero app. Not sure what I’m doing wrong on this.
+1 . I used the Ant+ Power Meter Connect IQ app on my lowly Garmin 130 Plus to get a 4iiii and Favero RS-2s displaying and recording on the same unit. It recorded into the same .fit, and then i uploaded that .fit to www.compare-the-watts.com, which automatically detected two power tracks in the file and compared them. With all due respect to Mr. Maker and his analyzer (which I have also used and which I applaud), compare-the-watts does a very nice job and is free. The dev allows donations to charities and deserves a salute.
What was fiddly about the 130 Plus is that it wouldn’t let me choose which power meter was the “main” and which was the secondary…pretty much decided itself (the 530 and above let you choose I believe). Sometimes it would grab just one of them to put in both tracks. My habit became pairing the secondary and but then disabling it on the 130, which kept it from showing up as primary, while the app grabbed and recorded the secondary anyway (even though it was not “enabled”). I also tried to make sure I woke up the primary first.
When I did analyze the output, I found the 4iiii had a habit of reading 10-20W higher at low wattage (like below 150W), but that the gap narrowed as wattage went up and was pretty close above 225W. So recovery segments or easy rides showed higher wattage and skewed the average. Now I just use the Faveros for everything and don’t bother comparing. What’s the saying…a person with one watch knows what time it is; a person with two always wonders.