Zwift/P1 pedal watt difference


(D Littlefield CIS) #1

I read some of the other posts about P1 pedals but not sure they really apply. I have a Wahoo Kickr, P1 pedals and a Garmin 820.

I am sending my data to Strava and Training Peaks (for my trainer). I have found that the wattage on zwift is consistently 20% and sometimes 30% lower than the readings I get on my Garmin with the P1 pedals. I generally load my days training into zwift to apply the resistance necessary. I find that I have to start off riding to see where the difference is for that day then adjust the ftp in the workout to get the desired output on my Garmin. 

I can’t use the zwift to document the workout in TP because the readings are consistently lower.

Is there a way to get these units to mesh within a couple %? 


(Paul Allen) #2

I take it you are looking for a different answer. 

Do you do a spin down before every workout to make sure the trainer is calibrated?

Are the P1 pedals calibrated?

Are there any firmware updates for either?

Either one of them being out of calibration could be the cause of the difference in watts.

They are 2 different types of power meters. The P1 is closer to the source of power as opposed to the trainer which has some power lose do to friction and other factors. That may some of the cause for difference in watts. 

As trainer/power meter are consistent from ride to ride there should be little issue. I am not sure you can get them exact since they measure a different places, but they should be close then 20-30%.

You could mess with the difficulty setting to see if that narrows the gap.


(D Littlefield CIS) #3

Sorry, lol… I wasn’t dismissing what you said. Are you with zwift? If you are I didn’t realize. 

I have put the difficulty setting all the way up. I was just seeing what more options there may be so I can spend a day off just messing with it to try to get it figured out at once instead of this going on a long time.


(Paul Allen) #4

No I am not with Zwift, hope that does not make a difference.

I will give it some more though on your options, for now just make sure everything is up-to-date and calibrated.

I wonder if the difference is because the Garmin adds the 2 pedals watts numbers together compare to the trainers 1 number. I could be a fundamental difference in the readings but I think the difference would be under 10% is that were true. 

Could the bikes drive train need to be cleaned and lubed? Maybe you are losing a lot due to friction in the drive train.

I think your problem would be solved to Zwift supported external power meters controlling resistance of a smart trainer in workouts. If it were support you could use your P1 pedals and still get all the benifits of the Kickr. This is one of the top 5 requested features on the forum, if you do a search I am sure you will find a few threads about it.


(D Littlefield CIS) #5

OK, this time I linked the P1’s into Zwift as well as the kickr, HR, cadence… The Garmin module and the Zwift powers were nearly identical, great in terms of doing the workout… thanks for the help.