Advice on moving to a 32 rear

[aea730]

After mistakenly posting my question in the Bike banter section I’m having another go.

I’m currently running a 28 rear cassette on ultegra Di2. If I want to go up to a 32 rear what do I need for it all to work right. I have a full compact crankset. Can anyone point me in the right direction

[Crippo]

I suspect you’re running 6850. In which case you will need to make sure you have the GS mech and you will need to lengthen your chain.

[Harpoon]

Work out the chain capacity:

(Biggest cassette teeth – smallest cassette teeth) + (biggest chainring – smallest chainring)

Shimano provide a figure for chain capacity for each mech, so as above, you might need to change to a GS mech.

That said, some time searching will turn up people running mechs outside of the official spec, sometimes without problems or needing tweaks to the limit screws. I've also been told Shimano build some slack into the spec's to allow for people cross chaining

[JustinF]

Not sure the above formula makes any sense, for me that would give (32-11)+(52-36)=39, fairly sure I'm using 110 links...

Common methodology is wrap chain directly around largest rear cog and the big ring at the front without passing through the rear mech, add two links.

[moonigan]

Shimano 32 cassette works fine with the standard 6800 rear mech on a 50/34. Just need to make sure you don’t shift to big/big. No need for a new chain unless you are currently running a 25t on the back. May also get away with it on a 52/36 again make sure you don’t shift to big/big.

[Barchettaman]

You might get away with using an old 9-speed 32 tooth sprocket, if you've got one kicking around.

Remove the cassette from the wheel, and remove one loose sprocket and spacer from the middle of the cassette.

Replace the cassette on the wheel in this order:

32 tooth sprocket -> 11-speed spacer -> the rest of the 11-speed cassette.

I've done this successfully in the past with 10-speed cassettes so it might work with an 11-speed set up. It might save you a few quid.

[aea730]

moonigan said:

Shimano 32 cassette works fine with the standard 6800 rear mech on a 50/34. Just need to make sure you don’t shift to big/big. No need for a new chain unless you are currently running a 25t on the back. May also get away with it on a 52/36 again make sure you don’t shift to big/big.

Does the fact it’s a Di2 rear mech have any bearing on things, will it still run an 11-32 rear and 50-34 front on the standard cage mech you think?

[Harpoon]

JustinF said:

Not sure the above formula makes any sense, for me that would give (32-11)+(52-36)=39, fairly sure I'm using 110 links...

Common methodology is wrap chain directly around largest rear cog and the big ring at the front without passing through the rear mech, add two links.

That calc is not for chain length, it's for chain capacity.

http://www.chainreactioncycles.com/shimano-ultegra...

CRC said:

Maximum Sprocket: 28T/12T
Minimum Sprocket: 23T/11T
Maximum Front Difference: 16T
Total Capacity: 33T

[BMWBen]

moonigan said:

Shimano 32 cassette works fine with the standard 6800 rear mech on a 50/34. Just need to make sure you don’t shift to big/big. No need for a new chain unless you are currently running a 25t on the back. May also get away with it on a 52/36 again make sure you don’t shift to big/big.

Are you sure? I had a 30T on my 6800 with the standard mech, and it only just worked. Long term the mech wasn't very happy about it, the spring started to stretch and lose its springyness which affected shifting.

[DamienCBR]

I think you 'can' run a 32 rear with a 50/34 and a standard rear mech. When i did my Di2 i put the GS on from the beginning.

[JustinF]

I have a 32 and a 36 both under a GS mech.