Roadie rear mech (105) capacity – will it take a big cassette?

More a ‘theoretical’ question at the moment.

I’ve got a short cage 105 rear mech. The only difference I can see betwixt it and the long cage version is, unsurprisingly, the length of the cage.

If I run a single ring up front on the chainset (thus not needing to take up the slack between a 50 and 34t ring), does the short cage have the same ability to run up to a 32t rear cassette, or are their subtle diffences in the long cage version that enable the spread?

I had a borrowed road bike for a while. It had an old Ultegra groupset (53/39 chainring) with short cage rear mech. I fitted 11-32T cassette to make my life a bit easier and I had no issues with the mech at all.

road cassettes are not always happy with very large cassettes (not just the amount of chain to take up, it’s the parallelogram angles or something) but they will usually cope better than the manufacturer would have you believe and you can make things better by screwing in the B screw. FWIW I’m running 10-speed ultegra on a 30 sprocket and 11-speed 105 on a 32.

I have the current 105 11 speed on my kinesis crosslight, came with an 11-32 cassette if that’s of any help, guessing it’s a mid length cage though given it has a compact chainset. :/

Long cage just takes up the chain slack. Maximum sprocket size is determined by the shape of the parallelogram mechanism. 10sp 105 has a listed max of 28t, 11sp 105 has a max of 32t.

A short cage mech should be able to happily cope with the spread from 32t-11t, it’s whether it’s happy going into the 32t that’s the issue. Waaaay back we used to run short road mechs on MTBs – that was when 28t was a big sprocket, but we ran those mechs beyond max sprocket capacity without much problem (ie 32t with a 28t spec mech)

It used to be that road mechs swung in a flatter plane across the block, keeping the top jockey close to the sprockets of an eg 12-25 block. Suspect that’s less the the case now that 32 is fairly normal on the road.

I fitted an Ultegra 11-30 cassette to my 10-speed 105 last week with no problems. I did adjust the B-screw a bit and I changed the chain at the same time…
Having read the above, I wish I’d gone for a 32… 🙂

Yeah, it’s an 11-speed rear mech so I know the longer cage version will take a 32t. I did assume they hadn’t tweaked the swing angle of the mech so there was a fair chance the short cage mech would go up to 32t rear.

Maybe a bit of experimenting is in order.

Now, if only they did 105 11sp flat bar shifters (at a sensible price!) for the commuter….

How do they cope with swapping? If I had 2 wheelsets, road and cx, and casettes of 11-32 and 11-28, does anyone know or think they could be swapped without fuss?

28 is OK but I reckon one or two extra low gears will be handy on the all purpose (rather than cross race) occasionally.

I’ve only had issues swapping between bigger difference eg 12-23 and 12-32 – but could still make them work. Certainly no issues with the 2 wheelsets I’ve got for the cross bike – geared differently for similar reasons!

I cocked up getting kit for a new bike, and stuck a short cage running a 32 cassette. It could be made to work (just) after screwing the B-stop right it, but its clearly not ideal. Ordered a medium cage one now, so will have a brand new 105 6800 short-cage mech for sale in a few days.

5700 105 short cage goes up to 28 for reach. You need a longer mech to cover an 11-32.