Hi - very new to smart trainers and looking at purchasing one but will also need to purchase a separate cassette. My road bike is 12-speed (Shimano) so do I need a 12-speed cassette or can I purchase an 11-speed? Sorry if this is a daft question, just trying to understand it - any advice much appreciated.
You’ll want a 12-speed cassette. In a pinch you can run an 11-speed cassette as long as you’re in Erg mode and pick a gear that keeps your chain straight from front to back. The concern comes to mismatched chain and cassette / gear widths. Really recommend a 12-speed, though. For me, I also matched the exact tooth-count for each gear, too, so that in Standard or Resistance mode the shifting is identical inside and outside.
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First, I’d make sure whatever trainer you’re buying can accomodate a 12 speed cassette. Then, yes you should buy a 12 speed cassette and ideally you’d want it to match whatever cassette you have on your bike. So if you’re running and 10-33 outside, you should run 10-33 inside.
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Is this a brand new bike that you have on order? I ask because shimano hasn’t publicly released their 12 speed road stuff yet. I’m not sure we know what shimano’s road 12 speed with look like in terms of chain spec, cog spacing, or freehub. If the chain specs are the same as 11 speed and you only plan to run in erg mode (no shifting) then you could probably run an 11 speed cassette. But if it is like SRAM’s where the 12 speed chain has a different roller diameter then you will have to run a Shimano 12 speed cassette. In which case you will have to make sure that your smart trainer has the right freehub to mount it. If the smallest tooth is 11 then you might be good using the traditional HG freehub but if they go to a 10 tooth then you’ll most likely have to source a new compatible free hub for the new cassette.
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Does not compute. I mean I’m sure they have it under development but then if you have prerelease hardware you wouldn’t be asking here. Or do you mean mountain bike?
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There were some comments in the 12 speed shimano thread where people said that they were able to order bikes with 12 speed shimano stuff and their LBS gave them some broad details but I think they were still looking at several months of lead time.
Thank you all for your responses. Sorry to confuse you over the Shimano speed thing - my road bike is very old and is therefore probably using some obsolete setup! They are Shimano gears, 12 speed but using a 6 cog cassette on the back wheel. I’m now thinking from the comments here that it will be totally unsuitable?
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Ahh well yeah then that changes things…so it’s 2 rings in the front and 6 in the back? What trainer do you have?
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Yes that’s right - 2 front rings and 6 rear. I am looking at the Elite suito but I appreciate that it would depend on a) if my bike is compatible and b) if it takes the required cassette size. That is the issue I am having.
Your 6/7/8 speed chain will be too wide for an 11sp cassette on a trainer. You’ll have to set up a 6sp cassette on the trainer to be perfectly compatible. I think you could use an 11sp chain on the bike and turbo as set up and not shift instead let ERG do that but I am not sure how smooth that will be.
Also, with a bike that old do you know what the spacing between the rear dropouts is? It’s possible that it’s a pretty old standard that is too narrow for most modern smart trainers to accommodate. Maybe also provide what the bike is too if you don’t know all of these specs.
Now that I’m researching a bit it now sounds like their may have been a different system to connect 6 speeds cassettes vs 7+ speed (freewheel vs freehub). So if your bike uses a thread on freewheel then I don’t think it will work with the Elite Suito.
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That’s an understatement! Makes me realise that our language around the number of gears on bikes has changed quite a lot in recent years.
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Thanks for all your advice - and corrections! As a result I am thinking that this is a non starter really. Unfortunately the cost of a new bike and trainer together would be prohibitive so was hoping I could utilize one of my existing bikes. Both have the same set up though, with 6 rings on the rear wheel and either 2 or 3 in the front. Yes the language nowadays is difficult to make sense of, so thank you for your explanations - much appreciated.
Yup, I’d consider any of the many wheel-on trainers, if the goal is to use the older bike. It can be a far less expensive option and still provide the setup needed for indoor training.
I second the Kinetic Road Machine, but many other fluid and magnetic trainers can all work.
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Instead of a direct-drive smart trainer like the Suito, have you considered a wheel-on smart trainer model like the Wahoo Kickr Snap? That would allow you to use your existing bike but also have the benefits of a smart trainer, like erg mode. And they are less expensive than direct-drive trainers.
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Thanks all - I will look into these suggestions 
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Have you thought about some fancy smart rollers?
New Bike Day has arrived!
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I would start by measuring the rear wheel hub width - from dropout inside face to dropout inside face. 126mm = won’t fit on direct-drive trainer, you can use a wheel-on trainer or rollers; 130mm gives you tons of options.