Cycling UK Forum

I have a shimano 105 compact chainset, 50/34. The back cassette is 12/27, which now needs to be changed.

I was thinking of changing it to a shimano 105 11/28. I will be buying a new chain.

Is this possible? I remember reading a while ago that somebody had problems with this. I'm wondering whether I can go ahead and purchase the essentials, as I will be doing the job myself.

Obviously, I'm not 100% sure on this, and I would appreciate any advice.

Many thanks,

Michael

shimanos techdocs e.g.

http://techdocs.shimano.com/media/techdocs/content/cycle/SI/105/SI_5VN0B_001/SI-5VN0B-001-ENG_v1_m56577569830683908.pdf

say 27T max sprocket, 29T total capacity for the SS rear mech. Sounds to me that you are breaking both rules with 28T big sprocket and 33T total. If you are lucky it'll just run slack in the small-small combos, but if you are unlucky it'll do that and it'll 'interfere' between the large sprocket and upper jockey pulley regardless of 'b' tension setting....

Worth a go, but you might be better off with a different rear mech. If its just the total capacity, a GS version will fix it.

cheers

Cheers Brucey, thanks for the reply.

I run a 28 on both bikes, with short cage rear mechs. One is Ultegra, the other Dura Ace. Adjust your B screwcorrectly,and I can't see it causing you a problem. The Shimano specs are generally conservative. As always, these things are at your own risk!

I have been using 11/28 on 105 long cage, and ultegra x2 short cages since 11/28 came out no problems whatsoever except I wish there were more than 18 teeth !

I used a jimmied-together 13/28 with Shim 105 for a couple of years. I don't think you'll have any problems. In fact, my LBS mentioned that I could use an 11/30 with the current 10-spd long-cage mech, although I have no corroboration of this.

My wife runs a 30T on a long cage 105 with no problems

i would like to thank everyone for all the information. may just stay with 12-27
michael