Shifters last time i looked were about the £130-140 mark for a double, I am not sure they do a triple though, also most cassettes start at 11 a couple at 12 both in the 105 and higher
105
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CS-6800
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The only ones that fit how I ride are the 12-25.
If you are looking for a low gear on a 50/34 it would need to be one of the cassettes with a 32th so an 11-32
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Seriously who rides a 120" on a compact, would it not be better putting a 15th in the middle and drop the 11th.
Compare it it with the triple I just set up
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and 105 10sp triples are £125
Having said that it is a very viable option over a triple for the same (slightly extended) range.
Oops your were just talking about the rear mech.