Kinetic power vs stages anyone else have issues with kinetic readings?

trainer
power-meter

#1

So I’ve recently realized that my cranks are way too long, so I’ve decided to sell them along with the Stages crank arm. As a result I’m stuck with using the power form my Kurt Kinetic smart trainer until my new cranks/power meter arrive. The only problem is that the trainer is reading something like 40-50 watts higher than my stages, but only when going above around 200 watts. Has this happened to anyone else? I did an 8 min interval somewhere around VO2 max for a goof (without going very deep at all) and came up with an FTP that was 40ish watts higher. I haven’t been training much the last 2 months, so it’s definitely not a true reading. Besides that, it would have jumped me from 3.5 w/kg to 3.9w/kg lol. Does anyone know how to fix this? I did the spindown, tire pressure etc are all good.


#2

Sounds like you are doing everything correct. I had good results with my inRide but once I got a PM I stopped testing inRide when I was sure I was getting consistent readings… A few others have stated as the watts get higher they found inRide starts to be less accurate.


#3

I had the same problem with my Road Machine. Same bike, tire, pressure, and roller tension, but widely variable watts and spindown offsets. After setting a bunch of PRs and getting a new suggested FTP on Zwift, I decided a proper power meter was in order.

My training goal now is to get up to the watts I thought i had. :roll_eyes:


#4

haha agreed 3.9w/kg would be a nice lift for me!


#5

What I fidy was play around with the wheel circumference so that my Stages matched as closely as possible with my KK in the power range that I’m interested in.


#6

thats a really good idea thanks


#7

I’ve used both simultaneously and they offer up very similar readings.

Are you calibrating the KK before each ride?


#8

There’s no calibration on the KK as i’ve only got a stupid one! The only thing you can do i ignore the 1st 20minutes as it warms up


#9

I’ve done a lot of riding with an InRide 2 and Powertap wheel, comparing numbers. That’s shown me which spindown time and roller pressure comes closest and I’ll redo spindowns at different roller pressures until I get the spindown I want - then I don’t change calibration unless I change bikes on the Road Machine trainer. My general advice is to calibrate after warmup then take 1/2 turn off the roller pressure. That gets my InRide reading 5-7% low below ~120w, accurate from 150-280w, and 5-7% high above 300. If you have a long wait for the new PM, do a ramp test on the InRide and use those numbers. Just put an annotation on your training log to remind you why there was a jump up then down in your FTP during those weeks.


#10

yup yup calibrated/spindown test with every ride.


#11

thats a really good call thanks. I set a temporary FTP but I think since I’m having fit/knee issues anyways I might just make this a recovery week until the new pedals arrive next week sometime.


#12

But if it’s a smart trainer with the Bluetooth thing you can calibrate it. The 21mph spin down.


#13

I have been scouring the forum looking for a post like this, thank you!
Do you recall what your spindown time was at that optimal point?
I typically calibrate after warm up and I noticed it can range between 1.77 sec to 1.52 sec. The slower spindown is what I aimed for today, when I did Mills.


#14

I haven’t used by KK for quite a few years now since switching to Kickr and subsequently Tacx Neo. However the KK with inRide definitely read much higher for me than the Kickr and Neo.


#15

You’re welcome. 1.82 - 1.90 is the range I use (1.86 basically) on my current combo, but it changes with different tires or wheels. I use 3 1/2 turns and 1/4 turn can move the readings ~5w, tire pressure can change 15 psi w/o much effect. Keep in mind even at its best the InRide under reports ~10% below 150w and overs 10% or more above 300. I assume a stronger rider with a PM could could learn to adjust the InRide settings so a higher wattage band was accurate. In the end you need to borrow a PM for couple days and the best you can hope for is not wildly unrealistic numbers.


#16

Thank you very much for the detailed answer! I had a whole wall of text diving deeper into this however after re-reading some early articles by @Nate that he wrote prior to developing the spin-down, it looks to me like you are absolutely correct. I would need to borrow a PM and perform my favorite type of science experiment: The Stare and Compare.
Ultimately what is important is that I set it up the same way every time. This way if the power is off, it will be consistently off throughout my training.
Thanks again Cheers!