Smart Trainer/Zwift power versus P1 power

Mark Hickman

Interested to see if anyone else has FTP tested using different readings/input for same test and saw a large delta.  Long story short, did Zwift FTP test today with Zwift reading from Elite Direto trainer while simultaneously running P1 pedals to head unit.  FTP results: Zwift/Direto ~ 253; Head unit/P1 ~ 221.  P1s were also reading about 141mph while soft pedaling, and .1mph when going hard, but that's something else.  

I understand I will continue to train with metric relevant to the platform I'm reading from, just wondering if anyone else had seen the same large delta, and how it might have translated to once the bike came of the trainer?

Happy New Years
Mark

Al Truscott

While it doesn't really make sense (pedals are closer to the actual generation of power than the rear wheel, where the trainer is picking it up) I also seem to get lower numbers from my P1s than from my KICKR. Since I plan on using the P1s and not the trainer in races, I decided to use the option to have the KICKR be "controlled by" the P1s, so that all #'s look the same no matter what is picking them up. I don't understand how that works, but it does eliminate confusion. I don't know if your smart trainer has that capability.

Also, periodically calibrating both the pedals and the smart trainer is probably a good idea.

As to the P1 "speed" - well, they are not designed to measure or report speed, are they? Just cadence and power? 

Gordon Cherwoniak

@Mark Hickman I've only done 3 rides in Zwift and using a powertap pro (9 years old).  I believe my numbers are quite similar but will need to check my pain cave computer tomorrow as I have my wko3.0 on that computer.  Today's ride Strava is reporting my average watts at 199 (1 hour 11 minutes) while Zwift had me at 212 (1 hour 1 minute).  I soft pedaled after the race to cool down for 10' so I'm fairly confident that the two are close for me.   

32 watts seems like a big delta.  Given the difference it does make you fell something is not right somewhere.

As for your transition to the outdoors, many people have a different number which is typically higher outdoors thus just plan to do a FTP test when you head outside to confirm your number. 

KARL BONNER

I use Garmin vectors, the only time they and my Kickr have a large delta is if I don't calibrate both, if I calibrate both, they will be within 1 - 2% of each other.(although they do say the Kickr doesn't need calibrating for every ride, being a bit retentive :-), i like to for peace of mind) 
I did a zwift race today & forgot to calibrate my Kickr, the readings are quite different to my vectors (which i calibrated), 11w difference between the two, enough to make a difference if you are relying on accurate data.
If I'm going to do any kind of test, I will always use the power meter I'm going to use on race day.

Gordon Cherwoniak

My wko file has 214 watts for the 1 hour 1' segment.

Shaughn Simmons

I second @Al Truscott thoughts on the P1s accuracy over the smart trainer.  I would also add, using the P1s as your baseline will allow you to move easily to the outside arena and transfer like power numbers given the P1s move with the bike when you ride outside.  It is tempting to go with the higher smart trainer number, and there is certainly nothing wrong with that as long as you are consistent sticking with that baseline in order to measure fitness gains consistently down the road.

Another option is to go with the smart trainer wattage for the rest of the winter and retest again outside in the spring using the P1 pedals as you move to more outside rides and get closer to your race date(s).

SS

Mark Hickman

@KARL BONNER
@Shaughn Simmons
@Al Truscott
@Gordon Cherwoniak

All; thanks for the feedback.  I calibrated the pedals prior, so not sure if that is what was causing it.  I'll continue to track both numbers when I test, and then try to find a course to test again whenever I start riding outside again.  Biggest concern for me will be dialing in the "2.5 hour power" for the 70.3 in preparation for Florida.  I may start to track the longer trainer rides on both as well to get a general baseline for how the pedals are reading and how I'm feeling.  Going to keep the trainer power pushing Zwift...cause you know...it's faster:o)

Jorge Duque

My experience with the P1s and the kicker is pretty good. I’m always within 1 or 2% difference. I calibrate both often 

Sid Wavrin

I also have a very large delta between my trainer and my P1's. I have continued to use the trainer for the Zwift Data, but I record the P1 data on my Garmin at the same time and save that data to Training peaks and use it to inform my training and track progress. I also find the trainer numbers may not be as consistent.