Help me understand caliper design...
There's one thing about most brake calipers that has bugged me, and maybe I'm missing something.
Most brake calipers have a large open section above the pads. In many cases this opening is large enough to allow the pads to be extracted through it.
If we look at a caliper, it has a huge slot through it, compromising rigidity. The pistons press inward and the caliper tries to 'open' itself, sort of like a book opening. The best way to keep this spreading from occurring is to connect the halves with the shortest possible brace: right over the top. Instead, most of these calipers have a huge, flex-encouraging opening right on top. They choose to route the (longer,heavier,flexier)bracing structure to the front and the rear portions of the caliper. Why?
I can see the practicality of an open-topped caliper when it comes to passenger cars, but on a bike, I can't understand it.
2 words heat , and weight
plus convenience, Ive never had a single issue with the caliper flexing open
Most of them are two piece designs with bolts located on the top that connects the two halves. They are stronger than the material and handle the loads. Even the one-piece BB7s had bolts located through it for strength.
wyrd bið ful ãræd
Easy of centering the caliper over the rotor and to change pads without removing the caliper. And to be able to monitor the wear of your pads ... Though I must admit that you can actually overturn your bike to inspect your pads for those calipers which has not got the 'slot' above.
Dissipation of heat ...
I am using the 2008 XT which is a 1 piece caliper and I think with a bike the forces that you apply to the pistons to stop a bike will be much lower than for a car and so the 'flex' issues you mentioned will not be a problem.
Martas, for example, have an 'enclosed' design like I was describing. There's no opening up top, either for pad removal or inspection. I don't run Maguras, but I know that they're among the lightest.
It just seems to me that in order to make something stiff, you want the structure to directly resist the forces.
I've never seen anything to indicate how much extra cooling occurs in an open caliper design. If it's mainly a matter of surface area, then a few fins would help there.
dont you know the holy grail of biking?
Originally Posted by D.F.L.
sure you can make pretty much any part on a bike stronger or stiffer, but at what cost? most people dont want a 45lb bike, nor one that cost $7000 because of all the exotic materials used. besides has anyone heard of any problems with calipers flexing open?no snapped bolts?
if it aint broke , why fix it?
Magura's have a slightly different design... they use a "single brace" of rather narrow angular section over the rotor. So, most air is swept in the direction of air flow. The pad/rotor interface is in the same direction that the air flows... think like a channel, with a brace on top.
Originally Posted by D.F.L.
Off course, you have to remove the wheel to change pads.
It's another way to skin a cat. Open back calipers are just a different design not any less weak or inefficient for the reasons others have mentioned.
Magura also uses fins on the hose connector to the caliper.
However... There is a drawback that I see to implement fins on a MTB brake... we ride on dirt and dirt sticks to fins reducing drastically heat dissipation. Remember dirt is mostly silica and silica has a crappy heat transfer coefficient. It takes just a little of dirt over radiating area to reduce heat transfer.