12-25 to 11-32 conversion

[Ajax Bay]

Yes, same freehub splines. A long cage RD has the distance between jockey wheel centres at about 88mm. You'll need that length cage for the 11-32 for wrap capacity. It's likely even though out of spec (I think) that judicious use of the 'b screw' will pull the guide jockey wheel low enough to avoid interference with the 32t sprocket.
For fitting you should not need to change the indexing: start from where you are, and tweak cable tension. New chain definitely needed, probably 2 inch links longer if current chain is correct length (or use chain round large and large and not through RD and add one inch link).
I now see @T4tomo has said much of this but just say that although 25t > 32t = 7t, the chain only goes round half the sprocket so 7/2 = 3.75, call it 4 more and that's 2 inch long links.

 

[T4tomo]

I presume sram and shimano both fit the same onto the Freehub?

Yes, for the vast majority of modern bikes the "spline pattern" on the freehub is either "Shimano/SRAM" or "Campag" compatible.

If you find something like this though, come back to us for further advice / ridicule....

 

[fraz101]

Doing some more research on this and can see I have the standard short cage rear mech which can take up to 28 max.

Im on 25 just now so I either go to 28 with some links added to chain or get the Wifli rear mech and a chain.

i guess 28 would be a decent help on the hills as opposed to 25……

 

[vickster]

Doing some more research on this and can see I have the standard short cage rear mech which can take up to 28 max.

Im on 25 just now so I either go to 28 with some links added to chain or get the Wifli rear mech and a chain.

i guess 28 would be a decent help on the hills as opposed to 25……

You could try the mech extender thingy linked upthread?

 

[Ming the Merciless]

How will I know that?

Check the leaflet that came with it.

 

[fraz101]

Check the leaflet that came with it.

Came with what?

 

[Ming the Merciless]

Came with what?

Derailleur. They all have a manual / leaflet. Look at it, either in paper form or online and you’ll have your answer.

 

[vickster]

Came with what?

I doubt you’d get parts leaflets with an 8 year old bike (especially if the parts were stock)

 

[alex_cycles]

The other option, perhaps not considered, might be to put smaller chain rings on the front?

 

[Ajax Bay]

Think you'll be fine with a 28t large for jockey wheel to sprocket clearance (NB b screw adjustment as required). Better to go 12-28 than 11-28. Wrap capacity should be OK (even if out of spec). If you want a shorter gear than that, then as @alex_cycles suggests, moving to a smaller small chainring (whether single ring change or as a chainset swap - depends on tooth count and BCD of current one) is a great though likely more expensive option. If a standard is fitted (53-39) then going compact 50-34 is viable. 34/28 is similar gear to 39/32.

 

[fraz101]

Think you'll be fine with a 28t large for jockey wheel to sprocket clearance (NB b screw adjustment as required). Better to go 12-28 than 11-28. Wrap capacity should be OK (even if out of spec). If you want a shorter gear than that, then as @alex_cycles suggests, moving to a smaller small chainring (whether single ring change or as a chainset swap - depends on tooth count and BCD of current one) is a great though likely more expensive option. If a standard is fitted (53-39) then going compact 50-34 is viable. 34/28 is similar gear to 39/32.

Thanks for that. New chain required to go from 12-25 to 12-28?
Its a standard double 53-39 on the front that I don’t want to change tbh

 

[roubaixtuesday]

New chain required to go from 12-25 to 12-28?

Probably not for length, but maybe for wear if matching to a new cassette. It's absolutely essential to check on the stand that the drive train will run on big/big, because if not, accidentally changing to that combo will result in catastrophic damage.

If it were me, I'd fit the cassette, then check with the current chain.

 

[Ajax Bay]

Unless the chain is on the short limit now, going from 25t to 28t will probably be OK without an extra (inch) link. Also see @roubaixtuesday 's sound advice (cross-post) ref wear. I would buy a chain as well so that if the old chain skips on the new cassette, I can take immediate remedial action.

 

[T4tomo]

I doubt you’d get parts leaflets with an 8 year old bike (especially if the parts were stock)

I doubt the SRAM website discriminates on bike age of those accessing it. if its like shimano's the leaflets from historically sold equipment are on there

Think you'll be fine with a 28t large for jockey wheel to sprocket clearance (NB b screw adjustment as required). Better to go 12-28 than 11-28. Wrap capacity should be OK (even if out of spec). If you want a shorter gear than that, then as @alex_cycles suggests, moving to a smaller small chainring (whether single ring change or as a chainset swap - depends on tooth count and BCD of current one) is a great though likely more expensive option. If a standard is fitted (53-39) then going compact 50-34 is viable. 34/28 is similar gear to 39/32.

I've never used a Sram mech, but shimano short cages rated up to 28mm will take a 29, I run a 12-29T on mine without issue - Miche Primato cassette, they also available in 10spd version if @fraz101 is interested - just google - make sure you get the shimano/ sram version.

I noticed a difference between 28 and 29T lowest.. I've never missed my 11T.

EDIT TO ADD:

ts a standard double 53-39 on the front that I don’t want to change tbh

No wonder you are struggling on hills - changing to a compact (50:34) would be a sensible option...

 

[vickster]

I doubt the SRAM website discriminates on bike age of those accessing it. if its like shimano's the leaflets from historically sold equipment are on there

The suggestion was (imo) to read the leaflet for the mech that came with the bike (Which is 8 years old and the OP had bought second hand)…not to go online and look up the technical information for the mech