Changing from 12/25 to 11/28 ?

[mikesw15]

I currently have Shimano 105 12-25 10S but want to change the rear cogs to 11/28 to make it easier to get up hills, Is it just a matter of switching them over or do i need to do anything with the chain ?

[cny-man]

Google "bicycle chain install (or length)" or check a video on this site. Odds are the chain will not be long enough for the 28 tooth. Also, if you can find a 12-25 the small cog will be more useful, as 11 teeth with anything more that a 46 tooth chainwheel is next to useless, and just spreads out the jumps between gears, possibly depriving you of a good cog in the middle range. Look at the mid-range cogs you use the most now and compare to what you get with a 12-28,

Odds are most any derailleur will handle a 28 tooth, but does not hurt to Google "(your derailleur model) capacity" so see how large a cog yours will handle in case you can go a bit more than 28 teeth such as a 12-30, which is much easier to find than a 12-28.
.

[mikesw15]

Thanks for that ;-)

[nfmisso]

Is 28 enough? A friend in MA who is serious rider uses 12-25 on most of his rides, but on the really mountainous ones, he uses 12-36. Do a real analysis of what you want before spending the money. For the mountainous rides he switches RD, chain and cassette. A 9S Shimano MTB RD (like M592) will work with 10S road shifters; 10S MTB RD will not.

[1FJEF]

Would it be worth considering a front inner chain ring change, go down a bit on the inner if it won't goof up the FD fit & shift? If it's like mine it's a bolted 130mm pattern I think.