A U brake is a brake that works like a centerpull caliper, only with the pivots mounted directly to the frame or fork. The "L"-shaped arms cross over above the tire, so the left brake shoe is operated by the right side of the transverse cable. A U brake uses studs (bosses) attached to the front fork or frame above the rim, rather than below it, as with conventional cantilevers. U brakes use the same type and placement of studs as rolle- rcam brakes do.
In 1986- 88 there was a fad for equipping mountain bikes with U brakes mounted underneath the chainstays. This provided a nice clean look to the seatstay area of the bicycle, and provided a somewhat simpler cable routing. In addition, as the chainstays are larger and more rigid than typical seatstays, the "problem" of flexing of the studs under load was reduced. Conventional cantilever brakes cannot be mounted on the chainstays, because they would get in the way of the cranks.
Although U brakes were cool- looking and powerful, the fad died quite abruptly when people actually started using the bikes that were sold with chainstay-mounted U brakes. They had several serious drawbacks:
* The inaccessible location made it very difficult to service or adjust the brakes. * They complicated the process of wheel removal. * They tended to get clogged with mud. * The mechanical advantage would decrease as the brake was applied harder, and as the brake shoes wore. * Due to the high-mounted studs, if you didn't monitor the brake shoe wear carefully, as they would wear, they would hit higher and higher on the rim. Eventually, they would overshoot the rim and start rubbing on the tire sidewall.
In recent years U brakes have been making a bit of a comeback on freestyle bikes.
==Einstellen von U-Brakes==