jacksonhandy

Thanks for the responses. I'll find a place to retest and go from there.

It isn't the same power meter, however they are both Quarq crank power meters. I'll have to test with each of them and see if they're significantly different.

PepeM

If they're both Quarqs they should be close. I was thinking more about if you were using a smart trainer, those can be way off.

jacksonhandy

Retested. Same protocol, 299w. lol. "Well, there's your problem".

miyata man

Are the new smart trainers at least consistent within 10% or so? Say every ride an hour in you recalibrate before getting down to business. On consecutive days is it going to yield close enough results to fine tune your effort with RPE.

I've no problem riding in 25F with 30 mph winds but the option to never run out road and remove all but one layer has some short term appeal.

valygrl

Single data point:

I have a Kickr SNAP and the calibration is both way off and internally inconsistent, I would not trust it at all. I tried to use it for intervals in ERG mode a few weeks ago, carefully calibrated it to match my powertap after about 15 minutes of riding. 40 minutes into the intervals, the watts started reading about 15% lower so my intervals were 15% too hard, i dumped it out of ERG mode and finished the rest of the workout targeting my Powertap power number.

I keep trying to get it to work in ERG mode and have mostly given up. If I didn't have a power meter to get a real number, I would have return it. OTOH, it's totally fine for Zwift as a controllable trainer, to mimic the resistance changes, and i just pair it as controllable trainer and get the power number from the power meter instead.

jacksonhandy

I haven't tried yet, and I also have a Kickr SNAP, but TrainerRoad claims to have an offset, where it measures offset of your powermeter and the trainer, then makes the resistance match the power from the power meter. It does it in ERG mode as well.

Zwift doesn't have that capability.

ancker

My indoor watts suck as well.

I have 4x powertap wheelsets, but train indoors on a Tacx Neo. It would be awesome to do a direct comparison between the two, but that's not possible. I love ERG mode on my Neo, but I simply cannot reach the same watts I can outdoors. That said, I'm still likely getting the intended training benefit as RPE/HR is roughly the same when doing similar efforts indoors vs outdoors.

I need to test outdoors soon, but it's a pain to have two FTPs to track. It would be nice to have a drop down in Garmin Connect/Cycling Analytics/Training Peaks to select the powermeter in use, so it can apply the appropriate FTP to calculate TSS/kJ/etc.

miyata man

Thanks, none of that was surprising. Actually doing the test to set zones for team trainer rides wasn't a waste even if my suspicions about the numbers it produced were valid. All I really wanted was a rough estimate of exertion to see about where 100w lies. Just to avoid going too easy outdoors with any number of things distracting from how much pressure is going to the pedals.

PepeM

Same here with a Tacx Genius.

TMonk

If I have a negative calibration value using my Powertap G3, are the power readings offset slightly low as well? It read -5 this morning and my 2x20's hurt. I can accept if they hurt a lot because I just wasn't that good this morning

TheKillerPenguin

I'm wondering the same actually, mine is reading 496 as of late (normal is 500 - 525). Also I need to do the firmware update still haha

TMonk

Yes you do haha. I remember when I updated mine and the values were centered around 0 - I thought it was broken

revchuck 

The numbers should be within +/-30 with the firmware update.

octaneTom

I discovered this online yesterday, then tried last night with success to allow the Kickr SNAP to use an external power meter for ERG mode:

The process
Using the Wahoo Companion App on your phone:

• Go to Saved Sensors
• Select your Kickr Snap
• Slide ON the "Control w/ ANT+ Power Meter" toggle switch
• Input the ANT+ Power Device ID (Zwift will display this ID number on the pairing screen...log in, check out the power meter ID number, remember it, then input it on the Wahoo app)

I did an ERG workout last night this way and the data on Zwift matched the power data my Wahoo ELEMNT Bolt was receiving from my Power2Max meter. I did notice the Bolt power jumped around the ERG number a bit — I think I have that field set as 1s power and the Kickr Snap or Zwift must be smoothing it a bit — but it was always right around that number.

Wondering now if I should turn off the ERG mode Power Smoothing toggle switch to get things more accurate. Will try that on my next ride.

Doge

On the 6 month old GS I ride with a Garmin 500 (I think) head unit. I was running at 0. This week it went to -3. Nothing really changed in temp etc. I don't know what that means as a % of power, but I did find it interesting it would just change like that. This is the stuff I ride, so I'm much less in tune with upgrade details.

TMonk

Right. Is there a correlation between the value of the calibration and the power readings? Or as long as it's within that spec it's the same - no offset?

revchuck 

My understanding is that calibrating the PT with the Garmin is like hitting the "tare" button on a scale, even though the number doesn't return to zero. As long as the calibration number is between +30 and -30, the power number is supposed to be accurate. I have no idea if there's any correlation.

ETA: I have three PTs - two G3s and a Pro+ upgraded to G3 specs. One typically calibrates at ~0, one at ~-6, and one at ~-18. My perception is that 250 watts feels about the same on all three. That's on three different bikes, one of which is my TT bike, so there are tons of possible variables in there. I feel they're close enough to train and race on.

TMonk

Hmm, thanks. Makes sense.

globecanvas

The number *is* the offset. If the device is working properly and you do a zero-offset, it should then display power accurately regardless of what the offset number was. The only reason to even look at the zero-offset number is that if it fluctuates wildly, that indicates the device may not be working properly.

TMonk

So does that mean that my 2x20' at 280 w was really 285 w ?

I know you can do the math - but my calibration was -5 this morning, which is a higher magnitude offset than I'm used to seeing.

revchuck 

Nope, it means it was 280.

ETA: IIRC, the offset is measured in Newton-meters, not watts.

TMonk

Ah - so it's a torque offset. Makes sense.

miyata man

I prefer the offset in RPE between quad shot of espresso and over trained. At least I have a vested interest in achievements gained through figuring out the inner workings of myself.

Are all PM's seriously still this flaky?

revchuck 

They're not flaky, they just require ten seconds to calibrate them before a ride. We ain't talkin' rocket science.

TMonk

We're discussing the nuances of data interpretation. The powermeter is still (very much) within spec.

In terms of performance, reliability and accuracy the thing has been rock solid since I started using it in the summer of 2013. If you're considering a PM I highly recommend the powertap.