Comparing my Kickr power to Power meter readings

barry_badrinath

Hello All,

I'm due to receive my crank from 4iiiii today, with a power meter freshly installed on it. I'm really looking forward to riding with power outside after a winter on Zwift with my Kickr (2nd generation).

However, I've been a little paranoid that my Kickr is perhaps over-reading, so am looking forward to checking this with the power meter. What would be the best way to do this? Record the Kickr on Zwift, and at the same time record the PM on my bike computer? I assume my bike computer wouldn't be able to record both at the same time? It is a Wahoo Elemnt, which does seem to integrate with the Kickr quite well - not sure if those readings would mean I wouldn't see the PM though.

I've seen there is a tool on DC rainmakers site that I can use to do that proper overlay comparison him and Shane Miller do. Is $5 for 24 hours which seems fair enough for the amount of use I have got from him!

markhewitt1978

You could record the power data from your Kickr using your ELEMNT and then pair Zwift to the power meter. If you then upload both of them to Strava then you'd be able to look at the results side by side.

CRAIGO5000

DC Rainmaker power comparison.

Use Zwift log against Headunit recording?

Man Of Lard

Of course with 2 power meters all you will know is either they agree or don't - it won't be possible to ascertain if one is reading high or one is reading low... since you don't know what the true figure is... (also your Kickr is reading at the "output" end of the drivetrain (so all the losses upstream are already lost) whereas your crank-based PM is reading nearer the input end (only pedal losses are already lost))

CRAIGO5000

I understand your theory, but every strain-gauge based PM should be accurate to within it's small printed doc i.e. 1%, 2% etc.

KickR's are optical-based speed sensing with clever algorythms built into the firmware which can sense hard stamps for a single revolution etc to mimic the immediate pickup a strain gauge would detect.

The power data collected by my stages (considering it's single-sided!) is within a single watt or 2 when cruising around and efforts etc all pretty much line up. Considering my KickR is a Snap (with it's "drive-train loss"), it's amazing how close everything is.

Certainly enough to accurately manage efforts, training indoors/outdoors and manage an overall PMC.

A few watts drift here or there will NOT matter. It's akin to probably not doing that extra 30 secs of training per day.

barry_badrinath

To follow up on this - was able to compare using DC Rainmaker's tool for a relatively intense Zwift ride. There was a small discrepancy with my Power Meter reading slightly lower, but it was never much more than 3% at 'normal' levels of power, and this could potentially be down to it being a left side only Power Meter. I'm happy enough with that!

MiddleRinger

That's a great result. You would expect some differences due to different power meters measuring in different places and one being single sided. Your L/R balance could throw off the readings easily enough. Only a 3% variance is well within a margin of error for that sort of testing. Now you have confidence your meters are both very close to each other.

penski

I was in a similar situation..glad you worked it out and thanks for the update!

airborne_warrior

My Tacx Vortex can read up to 100 watts over if not warmed up prior.

jmm434

Wow! Didnt realize warming up had that much of an effect. It says on the Wahoo kickr to warm up for 10 minutes before doing spin down calibration. I will make sure to do this from now on!