different designs of (caliper) brakes

why are cantilever brakes deemed good for tourers / mountain bikes,
but side-pulls or centre-pulls for "racing" type bikes. Surely you
need good brakes whatever, and though tourers might be heavier, racers
are likely to be going faster. Downhill there might not be much in it
in top speed. Doesn't everyone need the best available brakes?

Likewise, why different chainsets ?. I can understand hubs and gear
mechanisms as prevention of grit ingress is relevant.

Just idle curiousity as I've said, so not saying it's wrong

Hywel

in message .com,
hyweldavies ') wrote:

why are cantilever brakes deemed good for tourers / mountain bikes,
but side-pulls or centre-pulls for "racing" type bikes. Surely you
need good brakes whatever, and though tourers might be heavier, racers
are likely to be going faster. Downhill there might not be much in it
in top speed. Doesn't everyone need the best available brakes?

Cantis are more powerful. This is not such an issue as you might think -
dual pivot calipers are still enough to lift the rear wheel of a bike,
even with me aboard and I'm no lightweight.

I think the issue is that calipers are more aerodynamic - and on a race
bike every little helps. But it's also partly tradition. Cantis are used
in cyclo-cross racing, where the rims are often coated with mud.

Likewise, why different chainsets ?. I can understand hubs and gear
mechanisms as prevention of grit ingress is relevant.

Gearing, nothing else. Occasionally you will see a triple or a compact
double even on a professional racer's bike, on brutal mountain stages.
Usually the pros reckon to be going fast enough that they can spin 39x26
even on climbs, but when they don't they'll fit lower gears.

--
(Simon Brooke) http://www.jasmine.org.uk/~simon/

;; So, before proceeding with definitive screwing, choose the
;; position most congenital.
-- instructions for fitting bicycle handlebars

On 2007-07-14, hyweldavies wrote:
why are cantilever brakes deemed good for tourers / mountain bikes,
but side-pulls or centre-pulls for "racing" type bikes. Surely you
need good brakes whatever, and though tourers might be heavier, racers
are likely to be going faster. Downhill there might not be much in it
in top speed. Doesn't everyone need the best available brakes?

I think it's more that on a touring bike you need room around the wheel
for mudguards, and cantilever brakes are less in the way.

For a mountain bike you need plenty of space around the tyres to allow
for a coating of mud a few inches thick.

You might want higher-performance brakes on a tourer since you might be
going to load it up with a lot of weight and then ride it down
mountains. But I don't believe cantilever brakes are fundamentally any
different in performance to sidepulls or any other kind of rim brake.

Likewise, why different chainsets ?.

Just different ratios. On tourers you need the granny cog for carrying
your tent, pots and pans etc. up hills. On racers you don't because you
weigh 70kg and have a VO2 max of 88.

Mountain bikes also need the very low gears for getting up very steep
hills on rough terrain.

I can understand hubs and gear mechanisms as prevention of grit
ingress is relevant.

I suppose mountain bike hubs should also be tougher to withstand
thumping over rocks etc. but I don't know if they are.

As for things like rear derailleurs, what's the difference between
Alivio (supposedly a mountain bike group) and Sora (a similarly priced
"road" group, but available with a long cage)? Not much I should think.
Perhaps as you suggest Alivio is more mud-proof in some way.

On 2007-07-15, Simon Brooke wrote:
in message .com,
hyweldavies ') wrote:

why are cantilever brakes deemed good for tourers / mountain bikes,
but side-pulls or centre-pulls for "racing" type bikes. Surely you
need good brakes whatever, and though tourers might be heavier, racers
are likely to be going faster. Downhill there might not be much in it
in top speed. Doesn't everyone need the best available brakes?

Cantis are more powerful.

Not really, unless you mean that in some non-technical sense.

There are two basic metrics for a brake: how much mechanical advantage,
and how much power can it dissipate. All rim brakes should dissipate
about the same amount of power since that depends on how quickly the rim
can transfer heat to the surrounding air. Different pad materials might
make a difference.

Mechanical advantage may be higher for cantis, but not by much or people
would keep getting taken by surprise and thrown over the handlebars.

This is not such an issue as you might think - dual pivot calipers are
still enough to lift the rear wheel of a bike, even with me aboard and
I'm no lightweight.

Whether you can lift the rear wheel doesn't really depend (in theory) on
your weight, and certainly not on the power of the brakes.

It depends on weight distribution and on whether the front tyre has
enough grip, provided the brakes are good enough for the tyre grip to be
the limiting factor, but they should be on any half-decent bike. As for
braking power, that's more about how long the brakes keep working after
prolonged use without enough time between applications for things to
cool down. Assuming one's lifting the rear wheel from cold power
dissipation doesn't make any difference, unless it's so bad the brakes
overheat over the very short time taken to perform the manoeuvre itself,
and this is most unlikely.

In article , Ben C
says...
On 2007-07-14, hyweldavies wrote:
why are cantilever brakes deemed good for tourers / mountain bikes,
but side-pulls or centre-pulls for "racing" type bikes. Surely you
need good brakes whatever, and though tourers might be heavier, racers
are likely to be going faster. Downhill there might not be much in it
in top speed. Doesn't everyone need the best available brakes?

I think it's more that on a touring bike you need room around the wheel
for mudguards, and cantilever brakes are less in the way.

It's not really about being in the way, more about the lower mechanical
advantage and decreased rigidity inherent in long-reach caliper brakes.
Close-clearance race frames can use short calipers so don't have a
problem.

Cantis are more powerful.

Not really, unless you mean that in some non-technical sense.

There are two basic metrics for a brake: how much mechanical
advantage, and how much power can it dissipate. All rim brakes should
dissipate about the same amount of power since that depends on how
quickly the rim can transfer heat to the surrounding air. Different
pad materials might make a difference.

Mechanical advantage may be higher for cantis, but not by much or
people would keep getting taken by surprise and thrown over the
handlebars.

Wot, so V-brakes aren't more powerful than dual pivots, or dual pivots more
powerful than single pivots? I don't understand.

On 2007-07-15, Mark pleasegivegenerously@warmail*turn_up_the_heat_to_ reply*.com.invalid wrote:
Cantis are more powerful.

Not really, unless you mean that in some non-technical sense.

There are two basic metrics for a brake: how much mechanical
advantage, and how much power can it dissipate. All rim brakes should
dissipate about the same amount of power since that depends on how
quickly the rim can transfer heat to the surrounding air. Different
pad materials might make a difference.

Mechanical advantage may be higher for cantis, but not by much or
people would keep getting taken by surprise and thrown over the
handlebars.

Wot, so V-brakes aren't more powerful than dual pivots, or dual pivots more
powerful than single pivots? I don't understand.

I would expect them all to have about the same power dissipation since
they all work by clamping the usual rubber pads against the rim. That
works fine until at some point things get too hot and something bad
happens like the tyres blowing off (which may have been what happened to
poor Michael Rogers today).

There may be differences in mechanical advantage between those brakes--
in other words, with some designs a given force squeezing on the lever
will produce a higher force at the pads.

Higher force does not mean higher power dissipation or better braking
unless the mechanical advantage is so low that the rider's full strength
on the lever is insufficient to apply enough force to produce maximum
power dissipation.

The goal is not to maximize mechanical advantage, but to provide the
right amount of mechanical advantage.

Rob Morley made a good point which I understood as saying that if there
is a big distance from the rim to the fork, as you would find on a
tourer or mountain bike, then it may be harder to design a single-pivot
caliper brake with enough mechanical advantage. The different layout of
the frame dictates the different design of brake mechanism.

Wot, so V-brakes aren't more powerful than dual pivots, or dual
pivots more powerful than single pivots? I don't understand.

There may be differences in mechanical advantage between those
brakes-- in other words, with some designs a given force squeezing on
the lever will produce a higher force at the pads.

So when you say they've all got the same power, you meant in some flawed
'technical' sense, but in this strange thing we call 'real life' V beats
single pivot hand down. What's the reason for ignoring the massive
mechanical advantage of Vs over single pivots in your analysis? It all
seems a little bit 'bumblebees can't fly'.

in message , Mark
('pleasegivegenerously@warmail*turn_up_the_heat_to _reply*.com.invalid')
wrote:

Cantis are more powerful.

Not really, unless you mean that in some non-technical sense.

There are two basic metrics for a brake: how much mechanical
advantage, and how much power can it dissipate. All rim brakes should
dissipate about the same amount of power since that depends on how
quickly the rim can transfer heat to the surrounding air. Different
pad materials might make a difference.

Mechanical advantage may be higher for cantis, but not by much or
people would keep getting taken by surprise and thrown over the
handlebars.

Wot, so V-brakes aren't more powerful than dual pivots, or dual pivots
more
powerful than single pivots? I don't understand.

V (and canti, which are just a different implementation of the same
mechanical principle) are more powerful than calipers, because they have
more leverage and, because attached to each fork leg, are stiffer. Drop
for drop, dual pivot calipers have more leverage than single pivot
calipers. Short drop calipers have more leverage and are stiffer than deep
drop calipers.

As Ben C says, brakes operate by converting kinetic energy into heat energy
and then dumping that heat energy to the surrounding air. Given optimum
pressure on the rim, all rim brakes should be equal, because the limit is
how fast the rim can radiate heat. But in typical cycling that limit
condition is never reached, and it's clear that cable operated brakes
don't ever achieve optimum pressure on the rim, since Magura hydraulic rim
brakes are noticeably more effective in extreme braking situations such as
loaded tandems.

Having said that, almost any brake, if applied continuously on a long
enough, steep enough hill, will eventually build up enough heat in the rim
to blow the tyre off. The moral of which (if you want to slow down) is,
sit up and use your body as an air-brake; use your brakes when approaching
corners, let your rims cool on the straights.

--
(Simon Brooke) http://www.jasmine.org.uk/~simon/

;; Life would be much easier if I had the source code.

On 2007-07-16, Mark pleasegivegenerously@warmail*turn_up_the_heat_to_ reply*.com.invalid wrote:
Wot, so V-brakes aren't more powerful than dual pivots, or dual
pivots more powerful than single pivots? I don't understand.

There may be differences in mechanical advantage between those
brakes-- in other words, with some designs a given force squeezing on
the lever will produce a higher force at the pads.

So when you say they've all got the same power, you meant in some flawed
'technical' sense

I'm not going to apologize for attempting to clarify the difference
between leverage and power.

but in this strange thing we call 'real life' V beats single pivot
hand down.

Does it? I have never observed this phenomenon. The single pivot brakes
on my racer, on which the rim is very close to the fork crown, work just
as well as any other brakes I've used, including Vs and cantilevers.

What's the reason for ignoring the massive mechanical advantage of Vs
over single pivots in your analysis?

I already explained that.