What's my Offset?

Just bought a new Cyclops H2, and now I KNOW that my stages power meter has been cheating me on my power! Is there anyway TrainerRoad can tell me what my avg offset was for a workout? If this is already available somewhere, please someone point me in the right direction.

Offset is not stored continuously. It’s a one time value, like tare on a scale.

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Are you saying the H2 is more accurate than you meter? The number doesn’t mean anything but to the person using it. If your meter lets just say is 10% off it really don’t matter if you use power match and you always use the meter. If you use trainer power then go outside what power are you going to use?

I am a little leery of trainer power as from what I can gather none of them have strain gauges. They use some sort of algorithm from the spin down.

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All powermeters should be taken with a grain of salt unless you can accurately static test the torque.

I’ve been doing this with my powertaps for years – and sent a couple of them back to Saris for reading too high (I’ve seen some as much as 5% low, and some as much as 5% high, but they all tested within the +/- 2% at Saris – psst…that published accuracy figure has a lot of wiggle room, unless you’re dealing with SRM).

For improvement – is your performance going up?

For weight management – compare your PM to one that is known accurate (find a recently calibrated SRM, for instance) and see how far the kj are off. Or, if you perform a proper static torque test, see what the % error may be.

What makes you think that the stages is cheating you as opposed to the H2 being overly generous? Do you have a third reference point you’re comparing against or are you just taking the optimistic view of things?

As others have mentioned - which is correct is less important than which you can ride with more often. In this case you should be using the stages since you can’t really do too many outside rides with the H2 :wink:

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I know there’s variance in the power reading I get from both my trainer and stages power meter. I’m using the power match feature on TR, but it would be nice to know that arbitrary offset number.

Calibrate both, connect the H2 to TR in ERG and the Stages to a head unit. Do a ramp test and compared the power.

Voila. You’ll see how far off they are.

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Just guessing my power meter is off. It’s a gen 1 and the H2 is a lot newer.

I’ve done this quite a bit. I use the Garmin Vector 3S (single sided) and KICKR Core. I’ll run Erg mode on TR and then connect my Vector to my Garmin Forerunner 945. Every time I do it, I typically see an avg of 10-20 watts difference in my average power with the pedal being the higher. Normally I powermatch but the one ‘annoying’ thing is the power fluctuates a bit more with a single-sided meter. Still, like others have said, powermatch is best practice.

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That makes sense. Pedals should read higher than crank, which should read higher than hub based meters and with a single side pedal peter, 10-20w difference depending on leg balance isn’t that far off.

My Quarq and my H2 had good agreement and my NGEco was about 5 watts low. Not enough to make a difference.

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Yeah I think the level of difference is perfectly accceptable givent the setup. Probably more important is that I’ve tested this > 10 times and the watt difference has always been between 10 and 20 so it’s consistent.

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I think this is what I’m gonna do.

Also to clarify my above comment about offset and powermatch (which I didn’t parse correctly)

Power meter has an offset value that is like “tare” on a scale. It stores this value every time you perform a “calibration” (which isn’t actually calibration, it’s just telling the power meter that you don’t have force on the pedals).

The smart trainer has a “spindown” time that combined with temperature and other readings, calibrates it’s power profile.

Powermatch uses a model to figure out how much resistance to apply to the smart trainer to get your power meter to the power target. This gets better over time as you use power match more (if I am remembering correctly).

In terms of keeping everything tracking with Powermatch, here is what I’ve found to work well:

  • Calibrate smart trainer after a 10 minute warmup every 2-3 weeks
  • “Calibrate” power meter before every ride (i.e. perform zero offset) and do the same procedure every time. I spin the cranks around backwards a few times before I’ve gotten on and then I do the zero offset and double check the number. If it’s drifted a large amount relatively speaking, I’ll get on the bike, crank a few hard pedal strokes and then try again until I get a similar number twice in a row.

My stages reads 2-3% higher than the H2. The closer the strain gauge is to your foot, the higher it will read, generally. Hub based power meters should read lowest of all which pedals should read highest.

Why do you think SRM are superior in terms of accuracy out of interest?

Not when in PowerMatch. It is updated constantly, as the offset is usually not constant through the power range. It’s calculated by an outer loop on power requested by TR vs power reported by the trainer.

One of the biggest problem with single sided powermeter, is that the imbalance can be (very) different at 150w and 300w. I am at 60-40 at lower intensities and almost 50-50 at Threshold+ and VO2Max. In my case, it would mean that if I take the Ramp Test result (last one minute x .75), I would probably “under” train while doing sweetspot, tempo, etc… but it could be the opposite if your imbalance appears at higher intensities instead… Not sure if it’s clear :wink:

Regarding your setup, you also have the option on the Wahoo app to read the number of your Powermeter directly on the Kickr. It works wayyy better than the Powermatch! The Kickr will then just keep the power data of your Vector and deal with increase/decrease of intensities send by Trainerroad. Much better, trust me, especially with a single sided PM. Feel like Powermatch doesn’t deal that good with the more fluctuated data of this kind of PM!

Correct, in that the difference between the smart trainer and power meter changes in powermatch, which is specific to TR and not a device side setting. I realized that was what OP was referring to and clarified a few posts above.

“Offset value” specifically is a value returned by the power meter, which is generally static and not updated unless you have a power meter setting that auto-zeros based on criteria (like Quarq’s Autozero or P2M NG’s settings)

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I have the Vector 3s too and also see a difference of 10-25 watts, Annoying…

My first PM was a refurbished 1st gen SRM, in '98. I’ve used wired SRM, wired Powertaps, wireless Powertaps on my own bikes, and had loaners for 2-4 weeks with Quarq, Power2Max, and Stages.

I’d have the greatest confidence in a SRM that has been calibrated by their service center.