Changing Cassette from 11-25 to 12-27 Chain Length Question?

[Cletus Van Damme]

After a long lay-off I want to get back in the saddle, I have a dodgy left knee following a major knee op that did not go correctly. I want to change the gearing on both my bikes slightly. Both bikes, Specialized Secteur, Marin Mill Valley have identical 9 speed setups (except shifters on the hybrid). 9 speed Tiagra triple components. I have already changed the inner chain ring on both bikes from 30t to 28t after reading an old thread on here where PaulSecteur had done the same to his Secteur with no front mech issues.

Now I want to change the rear cassettes to 12-27t on both bikes as CRC are selling them for £15.99 which sounds great value to me. I would of possibly went for a little bigger but again as I read in the previously mentioned thread I believe this is the limit for the rear mech and I think the proposed setup will be adequate for the hills around here that I have to contend with (I avoid them if I can) and my knee.

So really all I want to know is how much would I extend the new chains for an extra 2 teeth on the new rear cassettes please? Would it be a simple 1 complete link or 2 complete links, or is there more to it than that? Sorry for my ignorance but I do not want to ruin 2 new chains, although the KMC ones are only around a tenner each.

Or does it matter to change the chains at all, as I cannot see me ever using the big chaining with the biggest cog on the rear cassette?

Thanks for any advice.

 

[Cletus Van Damme]

I should of searched better. Looking at this thread:

http://www.cyclechat.net/threads/9-speed-tiagra-11-32.117720/

I think I will try a SRAM 11-28t cassette instead, as it should work with my rear mech. That coupled with the 28t front chainring should be more than enough for hills. With the chain I think I will just make it too long and take links until it works I guess.