Brake caliper drop

[croissante]

Hi folks,

I'm currently in the process of building up a touring bike- an old Dave Yates frame that has been passed over to me. At the momentI'm in the process of acquiring all the components, but I'm not sure what length of drop I will need for the brakes. I measure the drop at 55mm using the wheel from another bike, which puts me slap bang at the extremities of drop length for the brakes I've been looking at. Options seem to be 47-57mm or 55-73mm (Tektro brakes). My dad suggests to go for the longer ones to have a bit more room with which to play, but I'm not 100% sure it's best if it turns out I need less distance, say 54-55mm?

Cheers

[Brucey]

if you have measured carefully, then -57 calipers should be OK. But I'd want to double check that (perhaps using another set of calipers or something) both front and rear before buying new ones.

BTW if it is a Dave Yates frame, he may be able to tell you what the frame spec is and that may save you some angst.

cheers

[drossall]

+1 for trying some borrowed calipers if you possibly can. I've measured brake drop ever so carefully and still had it come out wrong. Especially given that you're on the border of two sizes, if you've got an LBS that stocks both and will help you check, better to spend money there than save a few quid online and find you've got the wrong size.

[531colin]

Which will give the better M.A., a 57mm brake with the pads at the bottom or a 73mm brake with the pads at the top?
(That must depend whether the arms the cable attaches to are longer on the longer reach brake....bit of a missed opportunity if they aren't)

[pwa]

It's also worth noting that if you end up wanting to move a brake block up or down by 1 or 2 mm more than the calliper allows, you can safely file the slot on the calliper arm to allow this. Obviously you don't want to do this to a point where it significantly weakens the brake. I have done this without problems on several bikes, and I know others do it too.

[PT1029]

It is also worth bearing in mind, the brake pad on the arm that pivots on/about the centre bolt swings down to the rim (so as the pad wears may need moving up a mm or 2, and the pad on the other arm swings up to the rim, so may need moving down a mm or so as the pad wears. Only becomes a problem if you are unable to move the pad up (or down) as required if the brake arm is too long (or short).
I have often seen bikes where the pads need to be set fully at the bottom of the arms. As the pad that pivots at the side wears, it comes to rub the tyre as it cannot be lowered any further. Sometimes a slight fix for this is to swing the whole caliper off center towards the cable clamp side, and then re centre the brake, as moving if off center lowers the side pivot point.
If you rim has a braking surface wider (or deeper) that the pads you are using, this might not be an issue.

[tim_f]

It is probably not a co-incidence that the frame may take 'maxed out' calipers of the smaller size. A skilled frame builder like Dave Yates would have sought to do this on a bike that was not for racing.

As other have said trying it out with a borrowed caliper is probably the safest thing to do.

[croissante]

Cheers for the thoughts, folks- sounds like the solution is definitely to play with some borrowed calipers! I have access to the local bike co-op so I will head down and see what brakes they have in the bin, if there's anything the right length that fits. I have a long (55-73mm) Tektro front brake that I can test out as well.