Front derailleur clamp size

daniel_b

Hello chaps,

I will be looking to swap most of the gearset over from my Marin highway one onto my Felt F70.

The only exception being the Tiagra front changer.

Looking to purchase a 105 or Ultegra front changer, and have noticed that they either come in 31.8mm or 34.9mm clamp sizes.

Looking at it and making an eye judgement (with a tape measure) on it, it would appear the tube size is around 35mm, but is there anyway I can tell categorically?

Also, is there anyway reason, on the groupset swap the other way, that I can't still use the Tiagra derailleur with a double instead of the current triple?

Looking to order these bits in the nexxt few days, will be placing orders with CRC, Wiggle and Ribble!

Thanks

Dan

daniel_b

Anyone?

Is it literally just a case of showing a ruler up to the tube and making a judgement that way?

I had a look on the derailleur itself, and can't see the size etched anywhere.

Anyone else with a Felt who has changed their derailleur?

*Do I need to change my derailleur?

I've just had a closer inspection, the bike's spec is for it to be a triple, but I bought it 2nd hand as a double.

I can see 5 mounting points inside the now smallest cog, so does that mean that the derailleur should be capable of handling a triple? As it looks like it may have just been removed.

Question re the front brake lever/changer - this is only setup to be a double now, if I wanted to move it to another bike, along with the current cog setup, but buy a new 3rd cog, can I alter the lever so it knows it has a 3rd change to make?

Cheers

Dan

redddraggon

If it's an aluminium frame it's probably a 32 or 31.9mm derailler you want.

aracer

Simplest way is to wrap a bit of paper round the tube and mark where it meets. Open the paper out and use a ruler / tape measure to measure the distance between your marks - that's the circumference of the tube. Divide by Pi (3.14159) to get the diameter.
To a first approximation the circumference of a 31.8 tube is 10.0cm, the circumference of a 34.9 tube 11.0cm.

daniel_b

aracer - Genius - thankyou!

Dai_bach

Make sure you measure the diameter perpendicular to the axis of the tube. Even a slight angle can affect the measurement you make. If you can get your hands on a pair, vernier callipers make this task far easier.