|
Disc brakes have been lurking around for light years
on downhill rigs and other exotica, but it is only recently that
the technology has stabilised sufficiently to provide reliable
lightweight stoppers for cross-country bikes at a non-NASA price.
There's a bundle of reasons for getting excited about discs:
• You get truckloads of stopping power - even in the wet and even if
you ain't built like Twiggy.
• The braking surface is not immersed in mud, water and crap
on the trail.
• Rims don't wear out.
• There are no brake arms to wrestle with when removing a
wheel fitted with a wide-tread tyre.
• The good ones weigh no more than rim brakes.
• They just look sexy.
And as always some kill-joy needs
to point out the compromises:
• They cost more than rim brakes. Expect to pay an extra NZ$800- 1000
for a new bike spec'ed with discs front and rear. Retro fitting to
an existing bike, with disc-ready forks and frame, costs NZ$300-800 per end
plus another NZ$150-200 to build each new wheel with disc-ready hubs.
• Most models squeal a little when wet which is perhaps a small price
to pay but still annoying. Proper set-up and regular maintenance
can minimise this.
In my opinion discs are the best solution for off-road riding
- especially in winter conditions. If you and Santa are eyeing
up a new bike, then at the very least ensure it is disc-ready with
disc mounts on the fork and frame and if possible disc-ready hubs.
Disc Mounts
Annoyingly, there are two standards for disc mounts: the Hayes and the
International A-Type. Most manufacturers are moving towards the A-Type
but either is fine as adaptors are available to mix and match. If you're
dead keen to put a rear disc on a pre-disc frame you can get mounting
kits to do the job.
Hubs and Wheels
Because your rims don't wear out, and unless you regularly leap off tall
buildings and taco your landing gear, your disc wheels will last indefinitely.
So it's worth splashing out on good quality hubs, spokes and rims.
Disc only rims don't need any flat braking surface nor such thick sidewalls
so in theory can deliver the required strength with less weight than
their conventional cousins. They certainly look funky. Applying the
anchors at the hub results in large twisting forces transferred through
the spokes. Lightweight 15/16 gauge spokes, alloy nipples and Jenny
Craig radial spoke patterns might save 30g per wheel but you could
end up cursing the lack of reliability.
Hydraulic vs Cable
Early cable brakes were terrible - lacking serious stopping power. Equally,
hydraulic brakes often suffered when the oil became hot. The good brands
have got this sorted - the dodgy ones are still figuring it out. A
hydraulic system is easily balanced. Most designs take advantage of
this by moving both pads towards the rotor. Two-pot designs have one
hydraulic piston for each pad. Four-pot designs have two per side -
which allows for more contact area between pad and rotor and applies
differential pressure to supposedly eliminate squeal. Hah. With cable
and some hydraulic systems one pad is fixed while the opposite pad
pushes the disc against it. Different ways to skin the cat but both
equally effective in the field if designed properly
and regularly maintained. Some differences to consider:
• The most grunty hydraulic brakes deliver more stopping power but
that's only relevant if you're doing Jonah Lomu impersonations on the
Kamikaze downhill. Proper modulation is more important than absolute
power.
• Cable brakes are relatively simple. There's no fluid to leak and they don't
require bleeding. I like their "field maintainability".
• If you're retro fitting cable discs you can use your existing
break levers.
• Both systems are about the same weight although the lightest system
I know of is actually hydraulic.
• Hydraulic costs a little more - around an additional NZ$100
per wheel.
As always there are good and bad examples of both systems. Manufacturers
are constantly pumping newer, better, lighter models into the market
so before you buy bone up on the latest best buys. Magazine reviews,
talking to ya mates and a friendly bike shop all help to weigh
up the options. www.mtbr.com is
worth a visit for independent reviews.
|
