which size front mech?

crispy1980

Hi all, I'm looking for a new front mech for my mate's bike. He has a 31.6 mm seatpost and so needs a 36.4 mm seatclamp. I'm assuming that he needs a mech with same size clamp? Looked around but they only seem to go up to 34.9 ? Am I missing something?

nicklouse

there are only 3 sizes. see the how too measure a tube in the FAQs

and yes 34.9 is the largest.

does it use a band on mech?

looked on the makers site for more info?

crispy1980

It's a carrera vengeance ultimate Ltd 2010. It currently has a shimano altus on there but should come with a alivio. I've taken it off and it's just a single Allen bolt as per normal clamp on?

supersonic

Why do you need a new front mech?

crispy1980

The cage has been broken at some time and the piece is missing meaning it won't change up through the gears as three is no physical material to push the chain up

The Rookie

So you'll need a 34.9mm clamp, high or low mount depending on what will fit (same as you have now is the safe bet!), sized for the largest chainring you have (42 or 44 on most MTB's, ideally not a 48 for a hybrid/tourer) and with the right cable pull (top or bottom, most aftermarket ar dual pull), I prefer Shimano as they tend to be lighter than SRAM, but functionally no real difference.

crispy1980

What I don't understand is why he needs a 36.1 mm sharpest clamp but a smaller clamp for the front mech, when they both attach to the sane tubing?

cooldad

Presumably the diameter differs. There is often a collar at the seatclamp end.

The Rookie

crispy1980 wrote:

What I don't understand is why he needs a 36.1 mm sharpest clamp ?

Who said he needed a 36.1mm clamp? It's a 31.6mm seatpost and a 36.4mm clamp, although as it's a Merida I'd be suspicious of that, 34.9mm is much more likely.