disc brakes query

geepeetee said:

Hi

Are disc brakes on bikes a novelty or are they more effective?

The way i see it what you have on a bike is a large disc brake

anyway. The

Quoted message said:

traditional brake must be working on a much more effective diameter

(the

Quoted message said:

rim), but of course the newer disc brakes have a much larger friction

area.

Quoted message said:

These two elements considered, which is most effective.

later

Gary

Discs. Closer tolerances, away from the dirt and muck and materials
can be chosen for the job not the dual purpose of stopping and carrying
the tyre at reasonable weight.

General observation though is that cheap disc brakes can be much worse
than cheap rim brakes but good discs beat even the best rim brakes
hands down. Only Maguras come close.

Tony

in message <[email hidden]>, geepeetee

(') said:

Hi

Are disc brakes on bikes a novelty or are they more effective?

The way i see it what you have on a bike is a large disc brake anyway.

Yes, that's true. However the rim is often wet and, on mountain bikes,
muddy. The disk tends to get less wet and less muddy, and therefore to
perform a bit better in wet muddy conditions.

Also hydraulic brakes are much more sensitive than cable actuated ones
(obviously there are cable operated disks out there, and also
hydraulicly operated rim brakes).

Quoted message said:

The traditional brake must be working on a much more effective
diameter (the rim), but of course the newer disc brakes have a much
larger friction area.

These two elements considered, which is most effective.

In good conditions in the dry, rim brakes are at least as good as disk
brakes. Only in exceptionally horrible conditions do disk brakes have a
clear efficiency advantage. Disk brakes are easier to fit to some
designs of bike than rim brakes (e.g. monoblades). However, disk brakes
are inevitably heavier and more complex. So it's a tradeoff and there
really isn't a clear winner for all purposes. Most bikes you see with
disk brakes probably have them because the owner is a fashion victim
(but I have disk brakes on one of my mountain bikes, and like them very
much).

There's probably, overall, more difference in performance between
hydraulic and cable brakes than there is between disk and rim.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/

to err is human, to lisp divine
;; attributed to Kim Philby, oddly enough.

On Mon, 1 Nov 2004 18:12:21 -0000, "geepeetee"
<[email hidden]> wrote in message
<[email hidden]>:

Quoted message said:

Are disc brakes on bikes a novelty or are they more effective?

More effective and more predictable, for differing values of discs
(Hopes are good, the new Magura Julies are allegedly quite good, the
old Magura Julies were made of cheese and most (but not all) cable
operated ones are reportedly penc.

Quoted message said:

The way i see it what you have on a bike is a large disc brake anyway. The
traditional brake must be working on a much more effective diameter (the
rim), but of course the newer disc brakes have a much larger friction area.

But, as Tony says, on the disk there is a steel rotor and high
friction pads, the pressure can be cranked right up without wear
problems. Plus the rotor is not being dragged through the water and
mud like the rim is. And you can heat them to red hot without blowing
your tyre.

Guy
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geepeetee said:

Are disc brakes on bikes a novelty or are they more effective?

Can be either. Done /properly/[1] they're as good as you'll get, for
reasons outlined by the others. But a lot of them are done to look like
ones that are done properly and are no more effective than decent Vs but
heavier and wear out their more expensive pads faster.

If you're spending a four figure sum on a bike then basics like the
frame will be sorted and you might as well spend a fair chunk on the
best brakes going. But if the bike costs £200 then a set of discs on it
(a) won't be any better as brakes than Vs anyway and (b) will take money
from where it could be better spent, like the frame and transmission.

So on expensive bikes they're more effective[2], and on cheap bikes
they're a novelty.

Pete.

[1] "properly" equates with Real Engineering, which costs Actual Money
[2] assuming the money is spent on Real Engineering
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Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
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