So I have myself a nice new TaxC Flux S turbo trainer and needed to buy a cassette so that I didn’t have to keep swapping one off my bike. I ordered the cassette whilst away from home so couldn’t check my bike cassette physically and so googled to find out whether I had a 10 or 11 speed. Found my model and bought an 11 speed thereafter. Well I fitted the cassette to my turbo, attached my bike and away I went. Pretty good first session but alot of clunking gears, so after I finished a quick ride I checked and my bike actually has a 10 speed not 11 as my turbo is now set up with…
So my question is, as a novice, is this a big issue? I still seem to be able to ride and change gears albeit not as smoothly and quietly as normal. Can I just adjust my gears whilst on the trainer to suit the 11 speed and then as in when I want to go on the road adjust back to my bikes 10 speed? Doing more mtb in the winter anyway so not an issue right now. Pain to do I realise but I don’t want to fork out on another casstte just yet (especially as I’ve now used the new 11 speed cassette so can’t return) and wondered if there was any real issue with using a 11 speed cassette when my bike is set up for 10 speed.
Shouldn’t done more research or waited to check bike casstte before, but hindsight is great. Don’t give me to much abuse due to my idiocy 
appreciate its a rookie error but any advice would be welcome. 
Yes, it’s an issue because a 10 speed chain is wider than an 11 speed.
You need to get a 10 speed cassette, to match your chainset.
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I would think the chain would be the least of the problems, Your rear derailleur and shifters, unless they are friction from back in the 80’s, are indexed to match your gear setup. So you have a 10 speed derailleur on an 11 speed cassette. It will never match up even if you replaced the chain. I expect that you can not either shift into the smallest or largest cog but that’s not that big a deal. So what’s the downside if you use what you have? Your 10 speed chain’s inner dimension are the same as an 11 speed but the outer dimension is a tad wider so your shifting will be rough and could possibly jam. So you could replace the chain to avoid potential jamming but your shifter is never going to be smooth across the entire range.
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Thanks for the quick replys and for not humiliating to much!
So my road bike is a 10-28 speed, do I need to get a 10-28 cassette or can it be a 10-32 or other ten speed set up?
Also, my wife has a 9 speed cassette, am I right in thinking that her 9 speed bike could work with a 10 speed cassette?
You can use any 10 speed cassette within reason, it is limited by your rear derailuer and too big of a range will cause a problem. personally I don’t see going up from a 28 to a 32 too much of a jump. Please keep in mind that in Zwift there is something called “trainer difficulty” which is a slider setting from 0 - 100%. If really is a misnomer since it doesn’t make your ride harder or easier it just shifts you gearing. For example, if you wanted to keep the 10-28 but felt that maybe the 28 would not be easy enough then set your trainer difficulty to 10-30% and the 28 would feel like a 32. or more. You can play with it, its not set in stone.
Second part, Her 9 speed will not work with a 10 speed cassette for the same reason that your 10 will not work with an 11. To put her bike on the 10 speed trainer you’d either need to upgrade her drive chain or put a 9 speed cassette on your trainer.
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You don’t have to match exactly 10-28 to 10-28, you may use whatever range you’d like as long as your derailluer can work with it (you can find this information in your derailluer’s specification). Basically, if your derailluer has a short cage it will not work with cassettes having big sprockets like 34, 36 and higher. It will not be physically able to push your chain onto a big sprocket.
The 9 speed bike will not work properly with a 10 speed cassette for the same reason as 11 on 10. A 9 speed shifter has 9 indexed (‘preprogrammed’) positions while you need to have 10 of them for a 10 speed cassette. Also the cable pull in 9, 10 and 11 speed shifters is different. Jamming of a thicker 9 speed chain links in the narrower 10 speed cassette gaps may also be an issue.
UPD: I didn’t intend to practically copy Bob’s reply - we’ve posted our replies simultaniously. Pleased to see that I was not wrong, haha 
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Thanks, very clear.
If my wife was to try and use the 10 speed would the main issue be that she could only use 9 of the rings or is the spacing really so different that there would be further gear changing issues?
Just trying to find a solution that doesn’t involve swapping cassettes whenever we want to use the bike, which is almost daily and therefore a pain in the a** 
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Guess potentially the easiest and potentially simplest solution would be to upgrade her drive chain.
IF your wife’s bike has not been upgraded from an 8 to a 9 speed at some point and IF the rear freehub body can accept a 10 speed cassette then You will need a 10 speed cassette, right shifter, chain and a new rear derailleur. You’ll most likely be ok with your current crankset. You’ll also probably be able to get by with your current front derailleur but, because of the narrower chain, shifting may not be optimal. And yes, the left shifter and bottom bracket will be just fine.
Maybe time for a new bike or a second trainer?
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Thanks Bob. She has a 9 speed and although no real reason to upgrade (except for the turbo dilemma) her Bike is well spec’d and does not have a need to yet replace the gear set. However last night I took my 10 speed cassette off my bike, put that onto the turbo and her 9 speed worked like a dream, no clunky gear changes or issues at all. So although not recommended, this seems to be a problem solver for now, but I agree that it’s not long term even if there seems to be no issues right now.
Appreciate all the advice thank you!