Gear indexing: Indoor trainer vs Outdoor riding

I’ve recently had my gears indexed at my LBS and so far my gearing has been great on my outdoor rides., with smooth changes up and down the cassette. However, it’s not the same on my indoor trainer where the cassette can be quite jumpy/noisy, and it simply will not change to the biggest cog. I use a direct drive trainer and both my road bike and the trainer have Shimano cassettes (11-28 Dura-Ace and 105 respectively) so in theory there should be no difference (right?). Can anyone hep with this? Cheers.

If it works perfectly outside I wouldn’t mess with indexing. Did you try trimming with the left shifter?


Theory and practice don’t always align unfortunately! Your cassettes in each setup are in slightly different places, if it won’t shift to biggest cog then I guess the cassette on your trainer is a fraction further to the left (as you look down while pedaling) than it is when riding outside.

If it’s mechanical gearing then you can try increasing cable tension by turning the barrel adjuster on the rear derailleur anticlockwise one click at a time until it (hopefully) shifts cleanly and all the way to big cog on the trainer. Count the number of clicks and then you can reverse the adjustment when switching back to outside. The caveat on this is that if the limit screw is also preventing shifts to the big ring then personally I wouldn’t want to start changing both limit screw and cable tension every time I switched the bike. But cable adjustments alone ought to be able to get you clean shifting and you should be able to make do without that biggest cog indoors anyway.

If this if electronic shifting then I’m sure the same can be done, I just can’t remember how to do it! Downside of electronic shifting - it’s so good that once it’s set up right you never really need to touch it so I’ve never actually memorised what’s involved and have to get Google out on the rare occasions I do need to re-index.

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Is it electronic or manual shift?

Add a 2mm shim on your trainer freehub

I would not mess with the limit screw every time I switch the bike. I would accept not having the largest cog on the trainer and only adjust cable tension to stop the rattle.

Thanks all for the replies. I decided it was easiest to adjust the cable tension at the rear mech as suggested by @cartsman each time I change from the turbo to my rear wheel. It’s no hassle really and will keep my chain and the rest of my drivetrain happy. Cheers.