how often to clean chain at the moment?

[MikeS]

I would say go for the 12/36t cassette but first we need to know which brand/model rear derailleur is fitted because you might have an issue changing up to the 36t low gear.

I've looked up the spec on Halfords site and it says
Shimano 9 speed Alivio 11-34T Cassette. Given that I am having to order a one link shorter chain (116 rather than the 117 that is fitted from the factory), perhaps I would be stretching it a bit (literally) to go for the 36 tooth?
Mike

 

[sjpt]

Losing 2 links; you can't have an odd number. The factory one must have been 116 or 118; probably 117 plus link. Your new one will be 114 plus link. I'd go for the 11-34 and hope. You could take a couple of links out of the old chain and add it in (I think somebody already mentioned that), but be very careful trying that with a 9 speed chain.

 

[MikeS]

Losing 2 links; you can't have an odd number. The factory one must have been 116 or 118; probably 117 plus link. Your new one will be 114 plus link. I'd go for the 11-34 and hope. You could take a couple of links out of the old chain and add it in (I think somebody already mentioned that), but be very careful trying that with a 9 speed chain.

yes you are right the one fitted to the bike from new is 117 plus link. Using your logic the 116 version when it arrives will actually be 115 plus link, I will let you know. I managed to buy a chain last year and I think I got a crazy long one (about 126 links, and just took some out. But now I can't find where i got that.
Mike

 

[Tarka]

I found a set of quicklinks certainly help, very easy to undo and do up again.