Hi everyone,
When i’m on the biggest chain ring, I cannot get to the smallest cogs. It seems noisy as well and the shifting doesn’t seem smooth.
I went from a 11-34 cassette on my bike to a 11-28 on the home trainer.
I’m a novice so any advice would be appreciated
Without more detailed information about your setup (bike and trainer) it’s hard to say what the issue might be. My first thought, though, based on your description of the issue, is that you might have a different number of cogs on your road bike than you have on the trainer.
Assuming you have the same number of cogs on both your wheel and trainer…
The bike is a canyon grizl. The cassette is 11-34. I then bought the Zwift hub which came with a 11-28 cassette. Hopefully it clarified it a bit
Not really. How many cogs does each have? Are they both 11-speed?
Both are 11- speed yes. 
When you take the back wheel out of the bike, make sure the chain is on the smallest cog, then mount the bike on the trainer making sure that the chain goes on the smallest cog and then see what happens
You need to follow the video Paul has provided above. Can seem a lot to take in on first watch and first attempt but you’ll get there.
Would it make sense to remove it from the trainer, and do it all over again?
personally I’d get the same size cassette for the trainer as you’ve got on the bike, then you shouldn’t have to mess with anything
I’ll give it a watch. It does seem like a lot for someone without that much “bike mech” experience.
Should the amount of teeth on the cogs, 28 versus 34 pose an issue?
it’s worth a try but make sure the rear derailleur is in the right position to go on the small cog, so keep pressing the small right lever till it doesn’t go out any more
it could do as your chain is the correct length for the larger 34 tooth cog
that’s what i do and it makes it easy to flip back and forth - same cassette on both
Don’t forget the spacer which is behind the cassette. Sometimes a new cassette comes without it. If you don’t use a new chain for the trainer (to adjust the chain length), then you may have some noise small ring front and small ring back. i always use the same capacity cassette for indoor and outdoor use and a dedicated chain.
Thanks for the input - i’ve ended up buying the same cassette. Fingers crossed this solves it