UKC

Hi

If I were to change my rear cog from 12-25 to 11-28, would I need to fit a new chain or will the current one suffice?

Ta
Lee

In reply to lee birtwistle: How long have you used this chain?

In reply to Mike Stretford:

Its a brand new bike - was thinking of changing rear cog to suit hills round my way.

In reply to lee birtwistle:

Shouldn't be a problem with a new chain. You might want to check the capacity of the derailleur though, if the manufacturer has put a short cage unit on it might struggle with the larger sprockets.

In reply to lee birtwistle: I would have thought you'd be ok, you could try it and see?

I'm a dabbler rather than an expert (so this question is for anyone), but would it not be cheaper to change on of the front rings?

In reply to lee birtwistle:

It depends on how tight you current one is. When you are in the biggest cogs (front and rear) how far you can you push the rear mech?
Having said that as it is only 3 extra teeth you should be okay.

The other thing to bear in mind is if the chain has stretched the cogs on the cassette will have worn to compensate. If it is new chain then you will be okay but if it is old then it may be worth changing both as you gears could start to skip.

See link for more detail on chain wear http://cyclingtips.com.au/2009/03/how-to-check-for-chain-wear/

In reply to lee birtwistle:

I would give it a go in a bike stand to see if it works you might have to tighten the b tension screw a bit to get the clearance between the derailleur cage and cassette that is needed.

In reply to Mike Stretford:

It would be cheaper, but I think the OP wants to increase the gear range so you would have to increase the size gap between the front rings. In reality this would probably mean more awkward gear changes as you would have to shift both the front and rears mech to get the same ratio.

Good point about the cage size on the rear mech.

In reply to lee birtwistle:

Assuming you are on Shimano the standard (short) rear mech should accommodate a 28 tooth sprocket, you would need a long cage for the 30 or more tooth options

Your chain may need some extra links depending on how long it is now (try it and see). But as others have said it makes sense to get a new chain unless your cassette is relatively new

In reply to lee birtwistle:

I had planned exactly the same change last weekend but found I was missing a spacer. If you succeed please post the results. If I get it done first, I'll let you know how I got on!

In reply to lee birtwistle:
I made the same change for the exact same reasons on a 3 month old shimano 105 a few years ago, no probs it will be ok without a new chain, as mentioned the B tension screw will need screwing in to give more clearance for the larger cassette.

In reply to lee birtwistle:

I replaced my worn out 12-25 for an 11-28 last year and like it a lot for hills round here (lakes). If the chain is new and the derailer instructions allow this range then should be fine, although you may need to add an extra link via a quick link (can't remember if my new chain ended up needing to be a link longer, but I think this was the case)

In reply to lee birtwistle:

Technically, your chain will be 1 link too short.

If you take into account the other posters' comments/advice, you will be ok.

http://www.machinehead-software.co.uk/bike/chain_length/chainlengthcalc.htm...

In reply to lee birtwistle:

Changed from 12-25 to 11-28 this morning. No problems but as others have said, you probably should add one more link to the chain.

Otherwise, clearance was OK and no B-screw adjustment was required. In fact it's shifting OK without any adjustment at the moment. Will have to see what happens after it's bedded in.