Wahoo Kickr 18: Gearing, Heat, and Wear?

[avcall]

Summary: In ERG mode and for a given watt resistance, higher gearing (faster flywheel) runs cooler.

Original post:
It’s been well established that gearing in ERG mode affects virtual road feel. But how does the Kickr generate resistance (Friction? Magnet? Magic?) and does a slower or faster flywheel increase or decrease wear? I can imagine that it need not create as much resistance and therefore reduce wear if it’s going faster… but maybe not depending on how it creates resistance. ¯_(ツ)_/¯
I generally use the smaller chainring and a cog that keeps the chain straight, and the flywheel gets pretty hot after sweet spot or tougher workouts gauged to 250+ FTP. I’ve measured the outside of the flywheel as hot as 150°f (65°c).
I haven’t yet experimented due to the myriad variables I’m too lazy to control or track (workout length, intensity, room temp, gear selection), but will if nobody has already looked into this. What say you internet geniuses?

[stannoo]

I was wondering the same thing. I’m fairly new to the Kickr 18 and after a bit of gearing experimentation I settled on the small front ring and the first and second largest on the cassette, on the basis that I get a straight chain-line and these rings get the least wear on the road so I’ll even out the wear.

Whether this is a wise strategy I have no idea!

[nicrides]

Also interested in this! Kickr gets really hot after the workouts. Wondering if there’s something we could do to lengthen longevity.

[KRL]

I’ve experienced a burning smell and my kickr core getting extremely hot when doing prolonged ftp type efforts (ftp = 291) in the small 34t ring. I’ve since changed to the big ring and during any intense workouts the kickr generates far less heat and no burning smells.

[avcall]

Okay. I’ve started capturing ambient and flywheel temperatures before and after workouts, as well as gearing used during the workout. I’ll see if I can summarize what I observe when I get to the end of the short power build plan. Watts and time will be captured in normal course, is there anything else I ought to log? It won’t be super exacting science but maybe we’ll learn something.

[stannoo]

I dropped Wahoo support an email to see what they say. Not much as it turns out. Their only suggestion was to point a fan at the flywheel if it seems to be getting excessively hot (presumably on high resistance).

I think I’m going to mix it up more in future to try and even things out. 1 week inner / 1 week outer and a combination of cassette cogs.

[RONDAL]

FWIW i’ve done over 1000 rides on my KICK’14 and there have been no ill-effects. I’ve logged well over 2000hrs and the thing has been rock steady.
I’m interested in the definition of “hot”. My unit gets warm but its never been hot to the touch.

[avcall]

Last four workouts’ data in the table below. I’ll switch chainring and cog for the next four and post that for comparison. So far at a single gear ratio, the temperature is correlating more strongly with the average watts than total joules, duration, or other variable.

In case this table isn’t rendering well, I may just link to a Google Doc after I add the new data next week…

Date	Ambient 0	Ambient 1	Ambient Change	Flywheel 0	Flywheel 1	Flywheel Change	Flywheel Change Adjusted	Minutes	Average Watts	Work in kJ	Front Chainring	Rear Cog	Ratio	Cadence	Workout
22-Oct	62.5	66.5	4.0	60.5	150.1	89.6	85.6	62	203	762	36	19	1.894737	89	Mitchell
17-Oct	65.1	68.5	3.4	61.9	144.9	83.0	79.6	90	190	1027	36	19	1.894737	91	Lion Rock
20-Oct	62.0	67.6	5.6	60.8	141.1	80.3	74.7	90	185	1002	36	19	1.894737	91	Bashful +6
21-Oct	63.6	66.9	3.3	60.7	132.1	71.4	68.1	60	167	603	36	19	1.894737	90	Mokelumne

[Beneluxrider]

Might not make a difference but I always point my fan at the trainer after finishing my workout and Leave it on for about 15/20 minutes

[nvalphen]

Been on the kickr core for 150 hours or so since the beginning of this year. Almost always in the small ring. The flywheel does get hot (painful to touch hot) but never bothered to cool it or use the big ring… no issues so far.

[mcneese.chad]

It’s an interesting question. The slower flywheel speed should lead to less overall power consumption (and related heat) since it is easier to “hold” or restrain a slower moving wheel vs a faster one. Conceptually, I’d expect more heat and related problems from faster flywheel speed, since the resistance unit should be working harder to hold the related power.

All oversimplified speculation on my part, so I am probably wrong on one or more aspect of this. The only saving grace I could see with faster flywheel could be the faster speed in the air, which may make cooling better, but who knows?

[avcall]

To be clear, I’ve had no issues either and have no reason to think it significantly affects lifespan. This is more of an exercise in curiosity that could yield better understanding and potentially better durability. I would be a bit more detailed in my sciencing if this was more than a passing curiosity

[avcall]

I will still collect a few more samples at the faster gearing, but the difference is pretty stark after just one sample. Assuming this wasn’t some aberration, running the flywheel faster (higher gearing ratio) significantly reduced the temperature gain (faster = cooler). Note that I was not running either gearing at an extreme. I have a hypothesis that I’ll share sometime later this week. Anecdotally, it was also louder. Maybe I’ll measure that next time.
Data is here:

Wahoo Kickr (2018) Temperature Data

[purplecu22]

@avcall

But how does the Kickr generate resistance (Friction? Magnet? Magic?)

Most smart trainers us a magnetic brake to apply resistane.

[avcall]

So, it’s pretty clear to me that for a given watt resistance, higher gearing (faster flywheel) results in a cooler flywheel (faster = cooler). For a given gearing and rpm, higher watt resistance results in a hotter flywheel. I haven’t graphed out which has a higher relative effect, but both very clearly influence temperature. (See Google Sheet linked above.)
I’m also not sure whether temperatures plateau at some point but my testing saw the outside surface of the flywheel above 150°f (65°c). I’ll keep an eye on it as my workouts get harder.
I also don’t know what if anything else inside the trainer gets that hot or hotter. Nor do I know how heat tolerant those components are. I do think that in most cases, heat doesn’t “improve” longevity, even if it has a negligible deleterious effect.
For training purposes, I prefer the feel of the slower flywheel. I prefer the lower noise output of a slower flywheel. Nevertheless, I plan to use a higher gearing by default from now on to keep the temperature lower.
If anyone has more input or ideas, I’d love to keep exploring this.