Hi everyone,
I have a quick compatibility question. I currently own a Wahoo KICKR Core, but I found a Zwift Cog that was originally sold for an Elite trainer.
Does anyone know if that Elite-specific Zwift Cog will physically fit and work on the KICKR Core? Or do I need the āMulti-Trainer / Shimano HGā version of the Cog for it to be compatible?
Thanks in advance for any advice!
It should work if the gear ratio is close to Wahooās recommendations which are in this document.
The Cog itself should fit on any 11 speed Hyperglide freehub, which is pretty much all of them that come stock with smart trainers
Shuji at Zwift HQ here. Yes, The Zwift Cog will physically fit on any trainer that uses a Hyperglide-compatible freehub body. It is like any multi-speed cassette in that regard. Youāll need to remove whatever cassette is on the trainer, and replace it with the Zwift Cog.
To do that youāll need a Hyperglide lockring wrench and a chain whip tool. Do you own these tools and know how to use them?
FYI - the Elite-specific Zwift Cog has 18 teeth, all others have 14 teeth. This is because Elite trainers have a higher resistance floor than most, and the 18 teeth give you a physical gear ratio thatās a little bit easier to pedal when you want to go easy in game. On other brands, the trainer will adjust to the 18 tooth with a higher virtual gear, so you should have all the resistance you want.
Begs the question if thereās any point to a 14-tooth version? 18-tooth Elite version would effectively be universally usable?
Indeed. The question has been asked. 
A lot of trainers work (and feel) better at higher flywheel speeds. Slowing them down too much can result in a very sluggish and laboured ride experience. I wouldnāt recommend an 18t cog on a Kickr/Core/Victory/Hub/etc.
Then put the chain onto large front chainring?
That works on some setups. However itās not that simple. A 53 might be a little too big for some trainers and push them outside that ābest working windowā. I test flywheel speed in trainer reviews for this very reason. Iām sure thereās at least three people in this world who care for this level of detail in my reviews. 
And the Zwift Ride doesnāt have a large front chainring.
Interesting, though if itās really that sensitive, then I donāt know what to say. Certainly the Rideās chainring is larger than a common 34, or the small chainring on a triple, or a 39 in a 53/39 combo (which your somewhat alluded to). So, really, whatās wrong with 18t being the ādefaultā?
As above, slowing down flywheels too much can result in a very sluggish and laboured ride experience. This is something Iāve discussed in regard to virtual shifting not being suitable for everyone, even with a 14t and using a 42T chainring.
If Zwift defaulted to the 18t as standard on all trainers - Iād push back hard against this. It would be super convenient from a sales/stock/compatibility perspective. It would NOT be a good move for end users. End user experience is often overlooked, or even ignored, when it comes to commercial convenience.
The bigger picture here is the root cause of the issue - The trainers in question were never designed to be used with virtual shifting. That should in no way have a negative impact any other smart trainer.
Iām not really understanding obviously. Anyone on a virtual trainer but with a regular bike, could choose to use an eg. 50T front chainring and put it on the 11t cog in the rear. But that seems far from what Zwift would recommend. Pretty much the guidance has been to use the small front chainring, which almost always are going to be smaller than the Rideās 42.
Just for discussion, hereās a gear-inch mini-chart. Is there really a sweet-spot thatās best for virtual shifting? I highlighted the 42/14 ratio as I think thatās what the Ride/Cog combo is, right?
Thereās āclose enoughā to get most trainers within their specific best working zone of flywheel speed. The 14t presents problems with Elite trainers, not for others. Thereās also two issues at play here 1) trainer capability and 2) ride feel.
I really appreciate the questions / challenges to my comments @Wannie - itās making me reflect on the why/how/what of my experience with all these trainers to date. I could talk about this all day longā¦ but Iāll have to leave it here for now as Iām heading out for a ride.
Thanks for pitching in Shane, BTW I find the flywheel speed stuff you do really interesting. As virtual shifting becomes even more widespread, the value of that testing increases.
If āsomeoneā made a video that summarized gear ratio recommendations for some popular trainers, I would share the heck out of it. It comes up pretty frequently.
