How much difference between powersource is acceptable?

Hi all,

Iam using a old bike for my indoor setup (Wahoo Kickr Core) without a powermeter. Outdoor i use a Quarq on my roadbike and P2M on my winterbike. I have al ready done a advanced spindown on the Kickr Core. The Kickr Core reads a little bit higher than the Quarq, but @GPLama have reviewed the same: Wahoo Kickr CORE Smart Trainer: Firmware 1.0.10 // Lama Lab Tests - YouTube

Last days i put my quarq on my indoor bike to see if the wahoo kickr core give the same power.
Thats for me important because of WKO5. For the power duration curve and WKO5 model it is not accurate to give wrong power numbers, but what is in the range of acceptable?

I have compared 3 rides in Zwiftpower:
ERG workout https://www.zwiftpower.com/analysis.php?set_id=117631
Zwift race: https://www.zwiftpower.com/analysis.php?set_id=117627
SST in ERG mode: https://www.zwiftpower.com/analysis.php?set_id=119548

I see in the short efforts the difference are bigger than in the long efforts. I dont do a lot short all outs, so thats not influence the wko5 model negatif.

Do you think this is good enough or did i always use my powermeter on the indoor bike, what does that mean that i have swap my Quarq weekly between bikes…

Whatever you have…personally a few watts here and there aren’t a concern but over 5% and you’re not going to get accurate enough time in zones, which if you’re into WKO5 is probably a big thing.

A single source will always be the most consistent.

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This topic is a minefield…

I’ll accept the manufacturer -+% tolerance, plus a small % depending where power is being measured… and the effort. An on-bike meter will usually measure the spikes/accelerations better than a direct drive trainer.

A lot of the time people will excuse power differences using the extremes of both, pull in a drivetrain loss estimate, and tell you 30W difference at 200W is fine. (It’s not) Power meter companies love this too. It’s a get-out-of-jail-free card.

The root of the problem is that there’s no ‘standard’ power certification as such. Power meter companies self-certify, as do smart trainer companies. 4iiii came really close to doing some independent testing but fell short on their testing methods and published data.

Anyhow… back to your setup. The ERG tests look pretty good. You can do a static weight test on the Quarq to see if it’s reading ‘correctly’ at one point. If you don’t have a 10kg-20kg certified weight, using a set of accurate scales from a fishing shop (something with ~5g @ 20kg accuracy) and weighing something heavy and using that as your weight is a cheaper option.

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Thanks @GPLama ! I really appreciate that you replay on my topic.

I agree that the ERG mode workouts looks nice fit closely. What do you think of the Zwift race file? I think about to switch my Quarq in the winter from my racebike (i dont use it outdoor in winter) and rechange it back when i going ride more outdoor with the racebike.

you can do a static weight test on the Quarq to see if it’s reading ‘correctly’ at one point. If you don’t have a 10kg-20kg certified weight, using a set of accurate scales from a fishing shop (something with ~5g @ 20kg accuracy) and weighing something heavy and using that as your weight is a cheaper option.

My quarq is from 2015 and still i dont see big changes in numbers over years. It may be possible that the quarq measure a little to low, but when that is consistent i dont see any problem.

Looks as expected based on the ERG results. Either the Core is reading a little high, or the Quarq a little low… maybe… I assume the Core was recorded with Zwift? It does strange things with holding power for a second or so… another rabbit hole.

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Yeah indeed with Zwift. I have power smoothing turned off