What's the best way to set up calliper brakes re the bridging wire length?

[Cyclopathic]

Is it better to have the bridging wire between the two callipers short so it gives an internal angle of about 90 deg' or is a longer wire better with a more acute angle?

 

[PpPete]

Bridging wire? I take it you mean cantilever rather than caliper.
Got a few hours? Google "Cantilever brakes mechanical advantage"
Sheldon Brown is usually a good place to start.

 

[Cyclopathic]

Bridging wire? I take it you mean cantilever rather than caliper.
Got a few hours? Google "Cantilever brakes mechanical advantage"
Sheldon Brown is usually a good place to start.

Yes. Yes I did mean cantilever. The confusion crept in with them both starting with the same letter. And it was early and the coffee hadn't kicked in.
What really? Look it up myself? Aw...but I wanted someone just to tell me. I'm clinically lazy you know and trying to get it recognised as a proper condition. Thanks for the tip though. I'll ask uncle Sheldon.

 

[02GF74]

for optimum efficiency, I seem to recall the brakes need to be set so the stradle wires are at 90 degree - you could, and probably still can, purchase wire of different lengths.

 

[Cyclopathic]

Bridging wire? I take it you mean cantilever rather than caliper.
Got a few hours? Google "Cantilever brakes mechanical advantage"
Sheldon Brown is usually a good place to start.

Jees, just looked at the Sheldon page on this and my head hurts. I think I'll just sort of do it so it feels about right.

 

[PpPete]

Jees, just looked at the Sheldon page on this and my head hurts. I think I'll just sort of do it so it feels about right.

I do have some of these for which I still have the instructions, all my others get the "suck it and see" approach.
Within reasonable limits, shorter straddle cable = harder sharper braking
longer cable = more modulation

 

[mickle]

Shorter straddle cable = more mechanical advantage =more power and more modulation - but the brake feels spongy, which many people don't like.
Longer straddle cable = less power and less modulation but the brakes have a firmer feel at the lever - which many folks take to mean 'more power'. 'Cept they wrong.

Drop the straddle wire until it just clears the reflector bracket /mudguard/tyre. Put up with slightly spongy feeling brakes until you get used to it. You can't go wrong.

 

[mrandmrspoves]

Many later cantilevers actually have a straddle wire tube and an indicator to show the correct angle of 90 degrees

 

[mickle]

What you're after is a ninety (or more) degree angle between the straddle cable and a line drawn between the pivot and the cable anchor point.

 

[Cyclopathic]

What you're after is a ninety (or more) degree angle between the straddle cable and a line drawn between the pivot and the cable anchor point.

This does seem to be the consensus but there also seems a lot of room for adjustment to suit different types of cantilever brake for either harder or softer braking. I think I'll just take the 90 deg' as a starting point and adjust if it feels necessary.
I only really thought of it because I was reading a book on frame building for touring bikes and there was a shot of a bike the guy had made which had a really long bridging cable giving a bridge close to the h'bars and a much smaller internal angle than 90 degs. I assume he wanted more modulation than outright stopping power.
Thanks for the advice.

 

[RecordAceFromNew]

I am afraid the oft quoted 90 degree objective is a red herring, generally, and Sheldon's guide is not much help on this subject either. The only meaningful and helpful assessment (it is not a guide per se) of canti performance in the public domain, as far as I can see, is given here and in the associated links.

Imho the set up best practice depends significantly on whether the canti has a narrow, medium or wide profile. For narrow and medium profile models, the lower the yoke the higher the mechanical advantage/leverage/power, but the more demand it would then impose on rim trueness, pad/rim closeness maintenance and cabling system quality, or you would run out of lever pull.

 

[Cyclopathic]

^It's interesting but I think by the time I'd worked out how the graph actually related to a particular set up I was looking at I could probably have sorted it out by rough judgement and adjustment. The graphs do give an idea of the forces and principles very well though.