Assioma UNO constant 10W offset to L crank meter - not a % error - any way to correct?

Just got an Assioma UNO and test rode it today against my Gen 3 Stages L crank arm meter.

Good news is they tracked each other really well - except the Assioma is consistently reading 10W lower than my Stages L-only on same bike - same 10W +/- 1 W offset at all powers from 100-500W looking at durations from 20 sec to 20 mins. So unlike the typical problems where I see comparison of things like dual-side trainer power with drivetrain loss showing a few W difference, I’d expect better matching here. At lower wattages, this is well beyond 1-2% X 2 meters. At 500W, I wouldn’t worry about it.

I sprinted to make sure the pedal was well seated, and also verified the crank arm setting was correct. I could not find anything in the BOLT/ELEMNT software to override the Assioma setting either, so I assume that what I put in the Assioma app is what carries through?

Both were zeroed and re-zeroed. Tested it a couple times outdoors, and then indoors on trainer in ERG mode - consistently saw 10W +/- 1-2 watts depending on the selection period.

So, this is sort of good in that 10W offset is an easy value to work with mentally, but a bit disappointing in that I only see a % slope that I can apply in the Favero app - which would only be accurate for one power if I use it to correct this gap, and big enough to not be trivial.

It wasn’t completely clear if doing the static weight calibration could potentially rectify this - the app made it sound like this could help correct a constant offset, but one PDF I found showing the procedure made it sound like this may also end up just being a % slope change as well.

Anyone else run into this and are there any other tricks to put in a fixed wattage offset so I can match it to my stages meter and keep my data more in sync with existing data?

Check the crank/pedal pod gap is as per the Favero manual. iirc you won’t need to use a washer on a Shimnao crank. If you are using a washer, remove it (if space allows) and vice-versa. Retest. Don’t over-tighten the pedals with hulk strength either.

A static weight test will give you a better insight into which meter is closer to accurate. The Assioma app will give you a result that you can choose to accept or ignore. I tested a set of DUO (so, x2 UNO) with a 20kg weight today. L 99.84% / R 100.08% of the weight used. This is well within spec for the pedals and the variables using the test rig I have.

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Every single brand of PM out there reads low. :grinning:

Seriously though, head unit crank length overwrites what is on the pedal PM software. I am not a Wahoo user, but I think you set the crank length through the WAHOO companion software, rather than on the head unit.

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Short term answer maybe and a bit of a pain but set the % scale factor on the Assioma to most closely match the interval range of the workout or ride that you intend to do. Say a Threshold interval workout at 250W at +4% and Endurance Rides at say 170W at +6%.

I will try this - I had a washer with my existing pedal and kept it to make sure I wasn’t pushing it too close, but the recess on my SRAM Rival crank is very shallow and I’m pretty sure I can remove it. Sounds like you have some experience that > 1 mm spacing can cause a significant shift in reported power? I will also look into the static test but need to figure out where I’m going to get a weight for that.

If you can, I can’t find it - so would definitely be interested if anyone knows of such a setting! For what it’s worth, I’m at 172.5 which I think is often a default value anyway…

That’s exactly my plan for first test ride using it on new TT bike with no crank meter to watch in parallel :slight_smile: Far from ideal though…

It’s frustrating b/c the Assioma may well be more correct, but unfortunately I have a huge DB of power data, PRs, etc. that I want to stay consistent with - if I could easily retroactively drop all my legacy Stages data by 10W, I’d be fine with that too! Every PM should probably offer ability to modify reported values these days.

I’ve said on here before that I contacted Stages asking them if it was possible to adjust the reported power and if not were there any plans to. Their reply was basically “Our PM’s are accurate. Why would you want to change the power reading.” The irony is that virtually everything nice read and my own experience days that the Stages ones are or were generally the least accurate.

It’s so true - I see so many threads about meters reading low, but so few reading high :slight_smile:

For what it’s worth, I saw higher values than my Stages L crank when riding a dual-sided meter on vacation, thanks to 4% consistently higher R-side power. (I also see my trainer reads a bit higher, which is consistent with that observation)

Nonetheless, I didn’t splash out for the Assioma DUO even though it would have boosted my power data a solid 4%. But c’mon, I didn’t sign up for a 10% penalty either :laughing:

WOW - what a difference. Removed washer, reinstalled and did a new zero offset on both of the units again - really impressed with the result!!!

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This covered a few steps up and down in power with a 20 second burst in the middle. While riding I could already tell it was tracking much better than yesterday - and after 4 mins I should download and see…

One other difference here other than removing the washer - today, the initial pedaling after zero offset was done on indoor trainer. My understanding is that the assioma has a calibration period when you first start riding after the pedal change + zero offset? Yesterday, that would have been going down a hilly gravel driveway with a lot of bouncing and coasting. I wonder if that would be enough to cause a problem? For what it’s worth though, I did bring them to trainer last night, re-did the zero offsets on both, and the difference still persisted.

In any case, I’m really happy with this result - will probably do a couple more checks after pedal changes to ensure this is reproducible!

Needless to say, no concern about it reading 1% low - I’m OK to work that extra bit harder for the next wave of power PRs :laughing:

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Boom! Awesome result. And yes, the washer on/off and reinstall seems to influence things. I’ve found it depends on the crank used.

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Yea, so the crank in question for testing that has my stages PM was a SRAM Rival.

The one catch left is that the bike I plan to primarily use this on has a rotor crank that requires the washer - and I can’t put my Stages on it to verify the install :thinking: But I did at least use a clean new washer out of the Favero kit vs. my 4 year old crusty washer from the old pedal as I did on the first install!

The only way I can imagine getting close to verifying the result on the new bike would be to test both bikes against my Wahoo SNAP with the same rear tire - but even that would require resetting the clamp and doing a unique spin-down - and is far from the most reliable power reference. Still, maybe enough A-B-A-B testing could tell me if I had a 10W offset or a 2W offset… something for a cold winter day when I don’t want to do a real workout :laughing:

So, GPLama, I just installed Assioma DUO on my Ultegra crank but installed a washer. Why? My old P1’s used a washer. Just for confirmation, I should take off the washer?

Same question here, I always used a washer on my ultegra crank, wondering if this is not a way to go?

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On my R8000 cranks the clearance between the pod and one crank arm was a little over 1mm but the other side was a little under 1mm. So out of an abundance of caution I used a single washer one each side to ensure the 1mm min. clearance.

Due to me walking like a duck I’ve had to put 16mm pedal extenders on my a Ass Duo pedals. Do you think that will make a difference? Also have you any idea why a washer does make a difference?

Weird mine didn’t require a washer on either

dont forget to check that your shoe isnt hitting the pod on the Assioma.

I think mine would have been fine without one too but after installing them without washers I checked both with a feeler gauge. One side was ~1.1mm the other was ~.9mm.

One for Favero as they’ll know exactly how that’ll influence the readings of their gauges. I’d lean towards a ‘maybe’… Doing a quick static weight test on them would be worthwhile if you can get a certified/accurate weight to hang off them.

The washer theory - Again all guesswork - It’s possible the washer doesn’t face properly with some cranks and introduces a tiny amount flex/play under load. Maybe it’s just a reinstallation that’s reseating them better.

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When I have time I will likely try this again using the new assioma washers with the stages crank. I’d lile to see the same matching result with a washer present given that it’s necessary on the other bike.

In my original case, it’s definitely possible the old washer had some grit that made a less than perfect seating, so when I try this again, I will pay a lot of attention to cleaning the mating surfaces thoroughly.

One other note that is telling is Favero of course wants to ensure you don’t torque the pod into the crank arm, but other verbage in the instructions encourage you to use the washer only if necessary. It suggests to me that they must be aware of some risk with using them.

There are so few ways for a L crank meter to be wrong or erratic that I think it’s a good opportunity to test and retest the pedal installation procedure.

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