Largest cassette with 105 rear mech?

[penster]

I have Shimano 105 (2004) with a front triple chainset and an 8 speed rear cassette (currently 12-26). I would like to increase the range of the cassette to give a touring range. My ideal would be 12-32 8 speed rear. Will that go with this mech? Is there a rear mech I can use which will work with the 105 shifters?
Many thanks.
Mick

 

[fossyant]

You need a long cage rear mech, which you'll already have. Which model 105 do you have (there is usually a model number stamped on it) - someone will be able to tell you.

If you want a 32 rear, then I think it will be a MTB rear changer - look for 8 speed variants !

 

[Amanda P]

Fossy's right - there are, I think, long- medium- and short-cage 105s. If yours is the long one, it should work OK.

If you want to change it, well, I just bought an XTR derailleur to work with an 11-34 8-speed cassette.

Any Shimano mech should work with your Shimano shifters.

 

[TheDoctor]

You'll need an MTB mech for a 32 - a road mech tends to top out at 28. The geometry of the mech (ie road or MTB) is what governs how big the rear cassette can go. Cage length has nothing to do with it - that's just for wrapping up the spare chain.

You could get a smaller little chainring instead - a cheaper option. A 26T 76mm PCD ring will cost about £8 and go straight on. Currently running a Shimano triple with 48/38/24 (!) rings on a 13-26 cassette. It climbs walls...

 

[maurice]

An 11-28 works ok with my Tiagra 07 mech. I fitted it for touring in the alps with panniers.

However it's not as nice to use on the flat as you end up with bigger gaps between ratios. Sometimes I'll change down only to find the lower gear is too low, if you know what I mean.

 

[penster]

Cage length has nothing to do with it - that's just for wrapping up the spare chain.

You have just explained something I didn't understand. A triple front mech needs a longer cage on the rear because it will produce more spare chain when on the smallest front ring. Correct?
Mick

 

[andrew_s]

You will need an MTB mech for a 32 sprocket.

It isn't anything to do with the cage length. It's because the angle the parallelogram is set at isn't so steep for road mechs, and the top jockey doesn't move away from the axle so much as the mech changes towards low gears. If the mech does manage to shift the chain on to the big sprocket, the chain will be pinched between the sprocket and jockey, and it will run with a fair bit of noise and vibration.

Cage length is to do with how much spare chain can be dealt with as you shift onto smaller chainrings or sprockets. If the cage isn't long enough, the chain will be slack on small/small, and you will get the chain running across itself at the top jockey where the end of the cage has gone past the horizontal.

 

[penster]

You could get a smaller little chainring instead - a cheaper option. A 26T 76mm PCD ring will cost about £8 and go straight on. Currently running a Shimano triple with 48/38/24 (!) rings on a 13-26 cassette. It climbs walls...

I have a Shimano 105 triple 52-42-30 on the front. What is the smallest inner ring I can comfortably go to while keeping the 52-42 unchanged?
Mick

 

[TheDoctor]

Here's how I measured it. Get your bike into the lowest gear. Measure the gap between the bottom of the chain and the cross bit of the front mech cage - the bit that joins the inside and outside face under the chain. For each 2mm of gap, you can reduce the front small chainring by 1 tooth.