Originally Posted by
steltz02
The rear U-brake isn't really a 'problem' it's just not ideal (only from what I've read, not experienced) for touring for several reasons. 1.) U-brakes are hard to find at bike shops in the US and even more difficult in the third world making replacing them difficult. You need to bring an extra one with you and if that one goes down, you're out of luck. (obviously not likely, but you want to have the ability to replace all parts) 2.) Due to the U-brake geometry as the pads start to wear, they move closer and closer to the tire and must be repositioned or replaced or they will bite into the tire and ruin it. (easily alleviated with proper maintenance). 3.) Due to their placement they get filled with mud in messy riding situations and drastically lose stopping power.
Once again, this is not from personal experience, only from what I have read.
I've had a couple of bikes with chainstay U-brakes and a couple with seatstay U-brakes. As noted above the chainstay ones are a big problem in the mud.
However, I've not found availability in the US to be a problem. Any shop that caters to BMXers to any extent will likely have a brake that would fit (not all U-brakes will work under-chainstay).