Just out of interest… and because I’m going out of my mind here wondering what I’m doing wrong… has anyone installed a Shimano 12 speed road cassette on a H3 or H4?
The two smallest cogs on the Shimano 12spd cassettes now interlock and have less install tolerance meaning I can’t get a 8100 cassette on the H4 (and the H3) I have here. 11spd cassette installs fine.
I have installed a cheapy 12 speed HG cassette on my H3 so I could run my MTB on it. No issues.
I put a 12 speed Eagle NX cassette I had on my H3 for my MTB. Gearing is off (runs off the 12the gear but don’t want to mess with the adjustment or limit screws for when I put the wheel back on… maybe using the wrong spacer?) Anyway, I just find a middle gear that is smooth and use Erg mode. Works well as long as you don’t shift. 
The issue seems to be only with the new Shimano cassettes that have interlocking smaller cogs, Hyperglide+. The 2nd smallest cog won’t go on the Saris smart trainer freehubs.
I’ve been switching cassettes/hubs/wheels a LOT recently too, so I don’t think it’s user error. This has me stumped. The only thing I can put it down to is the lower install tolerance the small cogs now have compared to the previous HG splined non interlocking cogs. Not an issue on every other 11spd HG freehub I’ve installed the R8100 cassettes on…
Those use standard HG splines.
Can you just use an 11 spd for the trainer and not worry about the final gear? I think that should work for you-if you don’t need to shift through all 12 gears on the trainer.
That’s not a practical solution consider that Saris claims that the H4 is directly compatible with Shimano’s 12 speed cassettes.
Because I’ve wasted so much time on this, I’ll share what I think is happening…
In Short: Shimano 12 speed Hyperglide+ cassettes aren’t 100% backwards compatible with all HG freehubs. Not a Shimano issue. It appears to be a manufacturing/design/tolerances issue with non Shimano hubs.
In Long: See above. Really. This is some solid time wasting rabbit hole bullshit I’m dealing with… Measurements are best effort with a digital vernier by hand.
Right… The 2nd smallest cog on HG+ (R8100/R9200) is a different beast than 10/11spd cassettes that came before it. It interlocks with the smallest cog. I assume they’ve done this to give the 11 cog more bite/contact with the cassette/freehub. In doing this it looks like they’ve reduced the install tolerances of the cog to make it a tighter fit. See below. I’ll focus on the highlighted gap to make things easy… maybe…
Measuring the corresponding hub key/tooth width I get the following widths:
Those measurements correspond with how much ‘play’ the HG+ 2nd smallest cog has when installed. The Elite hub has the most play. The Wahoo and JetBlack hubs are a snug fit and has very little play. The cog won’t install on the H3 or H4 (or HUNT freehub… same reason but a different part of the freehub).
No surprises here:
Anyhow. That’s where I’m at with this. I sent Saris the images yesterday for comment.
If anyone has a HG+ cassette and a Saris H1/H2/H3/H4 I’d appreciate if you could let me know if this issue occurs for you too.
I got 12 speed dura ace coming in and I have the H3 & Hunt wheels. This is not sounding good
Dang, designs and tolerances for the loss here. Thanks for the work and reporting on this. Just a bummer that stuff can’t simply “work” these days 
I sent my H3 back last week with bearings issues. Now I cannot get them on the phone or no response on email.
In the designs and tolerances for the loss column, my park tool Shimano cassette lock ring adapter doesn’t fit over the QR adapter on the H3. So as I mounted my 10-speed cassette for my TT bike, I’ve only been able to tighten the lockring by hand. It’s not going anywhere, but a couple of the smaller cogs have a slight bit of wiggle and it impacts the shifting at that end of the cassette on the trainer. Pretty annoying, and I’m open to any solutions (even ones that will make me slap my forehead for being an idiot.)
I’m pretty sure the adapter doesn’t fit through the lock nut from the outside. I can dismount the bike and try it, but I think I already looked into doing it that way. It’s crazy to me that this is even a “thing” that requires any thought whatsoever. First for me in like 15 years of using trainers!
I’m over screwing around with this new trainer setup. Constantly adjusting things the last week to get it dialed… hopefully once it is I’m able to get as much use out of it as I did with the Venge just on the trainer on the floor! 
Get a lock ring tool that is also meant to install / remove the lock rings for disc rotors. This one worked in my H3.
Hello everyone, I’ve just bought the H3, coming from a TACX Vortex Smart wheel-on trainer. I’m experiencing some strange behavior with power measurements: it goes up and down without being “steady” at target power (see figure), something I’ve never experienced with the TACX trainer. I’ve updated the H3 to the last firmware and done a calibration before the workout. I’m running a 11-speed MTB Shimano SLX cassette if it matters.
Someone has the same issue and knows how to solve? It’s pretty annoying… Thank you!
This is what is supposed to look like - your previous trainer was lying to you
you could adjust the smoothing, but true reality this screenshot is normal
I see… Thank you for the answer, power smoothing is set to 3 seconds, gonna try with 5.
Yeah, there’s nothing wrong with that power graph. Your prior trainer using erg mode power smoothing was just lying to you.
Received my H3 back from Saris- this is what they replaced. The list means nothing to me but it looks like they replace a lot of internals.
I have completed a couple of workouts and things appear to be smooth. But I have notice a significant lag when the power ramps up on an interval. Like greater than 5 seconds.
