Band on Derailleur Size?

[EasyPeez]

Hi,

I need a new band-on front derailleur. I am planning on replacing a knackered Microshift jobby with a 105 5700. My bike is a 20 speed Boardman CX.

The trouble is, I have no idea what band-on size I need! I measured the tube at 140mm circumference and divided by 3.14 as per GCSE maths (now mostly a distant, foggy memory) to get a figure of 44.5mm

But the 105 only comes in sizes up to 34.9mm.

I'm guessing the issue here is with my measuring/calculating.

Should I just get the biggest option? Or be looking at a different brand of derailleur?

Cheers.

 

[S-Express]

take the seatpost out and measure across the top of the seat tube - that should get you near enough...

 

[Racing roadkill]

http://www.wiggle.co.uk/shimano-105-5700-10-speed-front-derailleur-d-band/

This will do it.

 

[S-Express]

http://www.wiggle.co.uk/shimano-105-5700-10-speed-front-derailleur-d-band/

This will do it.

Not if the seat tube is 34.9 it won't.

Useful guide here:

9cm seat tube circumference = 28.6mm clamp
10cm seat tube circumference = 31.8mm clamp
11cm seat tube circumference = 34.9mm clamp

OP either your maths is wrong, or you haven't measured the tube circumference correctly.

 

[si_c]

As per @S-Express I reckon your measurements are incorrect.

 

[the snail]

get a cheap set of vernier callipers and remove the element of guesswork

 

[Racing roadkill]

Not if the seat tube is 34.9 it won't.

Useful guide here:

9cm seat tube circumference = 28.6mm clamp
10cm seat tube circumference = 31.8mm clamp
11cm seat tube circumference = 34.9mm clamp

OP either your maths is wrong, or you haven't measured the tube circumference correctly.

The part I quoted will work, no need to mess around measuring the wrong bit of the bike

 

[S-Express]

The part I quoted will work, no need to mess around measuring the wrong bit of the bike

Your link is to a FD for either 28.6 or 31.8 dia fixing. So, if the bike requires a 34.9 FD, then it won't fit - which is the point I was making that you (still) seem to be missing..

 

[Racing roadkill]

The CX frame from 2014 / 2015 takes a 34.9 mm band front mech.

This one on the CX Comp

http://www.wiggle.co.uk/shimano-sora-3500-double-9-speed-front-derailleur/?lang=en&curr=GBP&dest=1&sku=5360535783&kpid=5360535783&utm_source=google&utm_term&utm_campaign=UK_PLA_Components&utm_medium=base&utm_content=mkwid|sXOyyfNgo_dm|pcrid|67090788902|pkw||pmt||prd|5360535783uk

This one on the CX Team.

http://www.microshift.com.tw/FD-R74.html

So this one

http://www.chainreactioncycles.com/mobile/shimano-105-5700-double-10sp-band-on-front-mech/rp-prod50487?gs=1&utm_source=google&utm_term=&utm_campaign=Chain+Reaction-UK-PLA-PLA-All-MB-SE-Shopping+QLB+Product+Mobile&utm_medium=base&utm_content=mkwid|s0Q2Zi6aR_dm|pcrid|161819986538|pkw||pmt||prd|179454UK

Comes in a 34.9 mm fitting, and will fit, the CX Team.

 

[Crackle]

I don't know which model year you have but currently the seatpost is 31.6 so I imagine the 34.9 will be the one but you really need to measure it.

 

[EasyPeez]

get a cheap set of vernier callipers and remove the element of guesswork

Looks like a nice tool, but having got through the last 38 years without needing any (or even knowing what they were) I'm not sure how much use I would be likely to get out of them.

Ignore me if this is a daft suggestion but you have the old one, don't you? Can't you use that as a guide?

No. I binned it when I couldn't get it to work loose. Silly really.

This one on the CX Team.

http://www.microshift.com.tw/FD-R74.html

This is the one I'm replacing, so I think @Racing roadkill is right about the one I need, but will take the seatpost out and measure the seat tube tonight to be sure.

Cheers.

 

[S-Express]

Looks like a nice tool, but having got through the last 38 years without needing any (or even knowing what they were) I'm not sure how much use I would be likely to get out of them.

but will take the seatpost out and measure the seat tube tonight to be sure.

This is one of those occasions...