Cassettes... it's a minefield out there

[migrantwing]

For 105 11speed, the next option from a 28T is the 32T.
The SS rear mech will take it, and as mentioned before, the B screw will probably have to be screwed right the way in.

The B screw on mine is about halfway in/out and works fine. On the other hand, I do need a few links putting in my chain to lengthen it a tad.

 

[migrantwing]

I have a long audax coming up with serious hills at the 100 mile point on Days 1 and 3 (of 75 hours) - Hardknott Day 1 and Rosedale Chimney Day 3. So have decided to try to manufacture a 12-30 cassette (9 speed) by buying an 11-30, removing the 11T (the 12T can be the 'new' outer one (has serrations)) and inserting a 13T from another used cassette (where the middle sprockets had worn). Will see how it goes. I may need to file off the wide spline on the 13T a bit to allow me to get orientation right to ensure the pick up from 12T to the new 13T shifts satisfactorily.
RD is a 105 RD-5500.
So instead of 11 12 14 16 18 20 23 26 30 I will have 12 13 14 16 18 20 23 26 30. With a 52T large chainwheel I'd be content with 13 14 15 16 etc (this would still give me a 108" top gear) but the bottom 7 sprockets are pinned: 14 16 18 20 23 26 30.

Is there a slight difference in inner diameter (where it sits on the freehub) of a 8/9 speed sprocket/cassette as opposed to a 10 speed? I would assume there is?

 

[Ajax Bay]

Is there a slight difference in inner diameter (where it sits on the freehub) of a 8/9 speed sprocket/cassette as opposed to a 10 speed?

The spline design (and therefore 'inner diameter') and lockring thread is the same. The 10 speed cassette is 0.7mm wider than a 9 speed. See Sheldon.

 

[tincaman]

Most freehubs will take 8/9/10 speed, a small spacer maybe required at times. The newer 11 speed requires a different freehub which is slightly longer. Shimano and SRAM cassettes fit the same freehub, but Campag is different

 

[MissyR]

Go for a 5800 11-32, it will fit your short cage rear mech. I am also confirm for anyone interested that the medium cage will handle a 36T.
But be prepared to have to get a new chain as well, yours may end up too short. Cassette is £23-£24, chain is £14, all prices sourced from Merlin cycles.

All bought so will see how it goes on the short cage. My mechanic is very good so hopefully i'll not need to buy the longer dérailleur

 

[Milkfloat]

All bought so will see how it goes on the short cage. My mechanic is very good so hopefully i'll not need to buy the longer dérailleur

Keep us in the loop - I am not as confident as @tincaman as I believe it will depend on the frame in question.