maximum size cassette on Tiagra GS (triple) rear mech

alfablue

My g/f is a newbie cyclist (1 month) and she has a Trek road bike with a Sora triple groupset. It has a RD-3400-GS triple rear mech and an 11-26 cassette. She is very good already and can cruise happily at 15-17mph on the flat but she crumbles a bit on hills. We are going touring in Wales in a few weeks and I think she needs a lower gear for the hills we will encounter (she has not done any serious hills yet, nor ridden a loaded up bike). I don't want her to have a miserable time (lets face it, it's gonna rain big time, anyway).

The Shimano site says the mech has a total capacity of 37T, and a min 11 and max 27 cassette. I know Shimano may be rather conservative with the specs, I am wondering if it is possible to run an 11-28 or 30 mtb cassette on this, or whether a smaller granny ring might be possible. I am not sure changing from 26 to 28 is worth it (though it may make just enough difference).

I tried searching but got nowhere, any advice would be appreciated.

topdude

If you have a triple chainset then i asume the rear mech has a medium or long cage so it should cope with a larger rear road cassette.
I think you can get a Sram cassette with a 28 or 30 tooth sprocket but any bigger and i think you would need a MTB rear mech to clear the much larger sprocket.