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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 |
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#2
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different designs of (caliper) brakes
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 |
#3
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different designs of (caliper) brakes
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. |
#4
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different designs of (caliper) brakes
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. |
#5
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different designs of (caliper) brakes
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#6
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different designs of (caliper) 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. Wot, so V-brakes aren't more powerful than dual pivots, or dual pivots more powerful than single pivots? I don't understand. |
#7
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different designs of (caliper) brakes
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. |
#8
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different designs of (caliper) brakes
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'. |
#9
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different designs of (caliper) brakes
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. |
#10
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different designs of (caliper) brakes
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. |
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