is this brake realy better then other cantilever brakes? I build my Orbea up with Tektro CR 720 front and rear (wide canti). I have seen that the Specialized Crux have on the front a wide, and on the rear a narrow brake. Is an narrow canti on the rear better?
Narrow gives you the ability to change mechanical advantage. With wide pads you're pretty much stuck with what you've got.
The first thing to do is get some cool stop salmon pads (file off the lip) and see what that does for you. Really only about 30% of your braking power comes from the rear anyways so it's not like you need a disc brake there or something.
If you're still not happy pick up some Shortys or something. No reason to get the Ultimates. Start with the stock straddle cable. If you're still not happy get a straddle cable carrier and a straddle cable and put it three fingers above the tire. That's a good starting point for more mechanical advantage.
+1 on the Kool-Stop salmons. I have set up some wide-profile Shimanos on the monstercross bike. Stock pads make you think you *might* stop. Kool Stop salmons will stop you *now*, change the performance to more like V-brakes. I've bought these for multiple bikes and they always make a big difference to me.
the ultimate's are the best I have tried, shorty 6 and 4 were and are crap. Spooky's are fine as long as you didn't actually want to stop. Pauls are great but expensive and more challenging to set up. Zero Gravity brakes are super light but squeal horribly. The wide profiles give more clearance, the narrow gives more modulation, but both have plenty of power to stop you. No one the pro teams running these right now are running them wide, even last week in the mud and muck.