Mountain Biking - Disc brakes?
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10-26-05, 11:14 PM
What are the difference between disc brakes and the chap kind, would it be better to spend xtra money for a bike with disc brakes.
10-26-05, 11:21 PM
I think it all depends on where you live. In the texas(in the middle of the desert) My (cheap) breaks work just fine. My buddie that has disk has had hell with them.
The main reason I went with disc brakes over rim brakes is that I can replace a cheap rotor instead of an expensive rim (more expensive once you factor in the work and time to move your old hub over). Not to mention they work better in wet conditions (but, then again, I've never used really high end rim brakes). An added side effect is that I bought easy to tweak calipers (Avid BB7s; I've put enough miles on my new bike to need to readjust for pad break-in and I did the initial setup myself) that are so wonderfully easy to adjust compared to any rim brake setup I've seen; not all calipers are so user friendly.
Here we go again:
The following has been reposted by me more times than I care to admit
Why are discs better than rim brakes?
The difference is friction. Friction is of course the force acting against the momentum. Friction under all circumstances will be greater in a disc system than a rim system. Not even ceramic rims and their pads can compare to the sustainable friction of a disc system. Not to mention the effects of inclement conditions on rim brakes.
Let's start by taking a look at the physics involved. There's a law of physics that states how an object in motion has a certain amount of energy due to its momentum. This energy is called kinetic energy. In order for this object in motion to stop or slow down, it must lose some or all of its kinetic energy. It does this by converting the kinetic energy to heat.
It's pretty simple. At your wheel you have a metal disc and a set of friction pads. The pads squeeze or push onto the metal. When this happens, you create friction. Friction generates heat, of course. Since the wheel is turning, then the kinetic energy of your momentum is converted to heat at this point and discharged harmlessly into the atmosphere (with a slight loss of pad material), and your bike slows down. The faster it is going, the more heat is needed to stop it. The more pressure you apply to the pads, the faster it can discharge the kinetic energy. The disc aids in the discharge of the heat generated. The surface area of the rotor allows heat to dissipate more quickly.
Rim brakes work well, but they have a hard time shedding heat well enough to prevent fade when used really hard. Brake fade occurs when the brake overheats dramatically; braking power is vastly reduced. The fact that rubber compound rim brake pads can only sustain so much heat and pressure before they break loose is another key point as is the fact that disc pads, being made of a more durable substance, are not prone to the same failures.
Disc brakes handle heat load and dissipation better than calipers.
They don't transfer the heat generated directly to the rim, like calipers.
Disc rotors are MUCH cheaper to replace than an entire rim (as low as $17). As far as being able to lock a wheel: yes you can lock a wheel much easier with a disc than you can a caliper of any type, however if your brakes are PROPERLY setup, you also have greater modulation with less effort than any caliper system ever invented.
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