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.
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.
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.
haha agreed 3.9w/kg would be a nice lift for me!
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.
thats a really good idea thanks
I’ve used both simultaneously and they offer up very similar readings.
Are you calibrating the KK before each ride?
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
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.
yup yup calibrated/spindown test with every ride.
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.
But if it’s a smart trainer with the Bluetooth thing you can calibrate it. The 21mph spin down.
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.
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.
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.
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!