Crank based Vs Smart trainer Power variance

seanin4711

Hi all,

did a workout yesterday on mywhoosh.

Elite Direto XR -power/cadence and HRM broadcast to app via BLE

Magene p325LS crank based PM/HRM broadcasting to Bike computer via ANT+

Started warm up for a few minutes before bunch ride.

Crank based power meter(magene p325 -30 offset) reads average 185watts for the 50mins.

Reading low?

elite direto XR

internal PM (updated and calibrated)reads average 235watts for the 50mins.

reading high?

Anyone any idea how there can be so much variance?

i feel the workout was closer to the elite but definitely not 185 average.

thanks

John

this.lad

I find the bike power meter and cadence meter to be more accurate.

For cadence the trainer is guessing at best I think.

For Power your power to the pedal would be greater than your power to the wheel, if youre using the same bike in and out id connect the power meter to zwift or whatever seperately and use the same source for all training if its a big thing for you.

Plastik

As an initial totally unqualified comment, I would side more with Elite being more accurate than Magene, who I've never heard of before this thread.

Why is elapsed time and total distance different between both workouts? Is the Magene continuing to record 0 power and moving in the avg even though you're stopped?

comete

Does it matter which is more accurate as long as they are consistent?

Just pick one and run with it? Not sure what training platform you’re using but you can set Zwift and TrainerRoad to take power from a different source than the trainer it’s controlling. I’d be inclined to use your crank based one for everything (assuming it’s consistent), seeing as it’s on your bike permanently.

There’s a <5% variance between my assioma uno and elite direto x (with assioma being lower though you’d expect the opposite due to drivetrain loss), which isn’t enough to bother me. I use my assioma ftp and live with my turbo workouts being 4% easier.

C91463FE-A60B-44DA-9FFE-1AC26A7E0172.png

dahat

@comete you can set your pedals to be single power source as I have. It rules out any variance for workouts.

comete

https://www.boards.ie/discussion/comment/120465212#Comment_120465212

Yep, had done that for a while but found the turbo slower to adjust in erg mode, so I just live with the 4% variance.

seanin4711

https://www.boards.ie/discussion/comment/120464671#Comment_120464671

warmed up for 2-3mins prior to starting bunch ride,hence longer distance on Magene

seanin4711

https://www.boards.ie/discussion/comment/120465185#Comment_120465185

Can i drop both .fit files into zwiftpower to compare?

thats the issue,both PMs are not on one fit file, hence cannot combine and compare individually

Macy0161

Turbo will also be total power, compared to left only. At either end of the stated accuracy, probably closes the gap too.

fwiw, I did see some variance between my 4iii left sided and my Hammer v1, but within boths stated margin of error. I ended up just sticking with the turbo power (and an old bike permanently set up) rather than swapping bikes.

seanin4711

https://www.boards.ie/discussion/comment/120468550#Comment_120468550

update

I needed new chainrings for training bike(any excuse) so as luck would have it picked up Powertap C1 chainrings for 150€ (old stock - unused) from bike rack.

Had them before but sold them for assioma pedals

dualsided power readings ANT+ & BLE.

perfect for what i need.

moved magene single to TT bike - all good in the hood!