Techniques for braking on steep descents

[Jon in Sweden]

This thread has grown arms and legs - quite unexpected!

It's been a very interesting read though. I was out last night on the bike that I used in the UK. But being back home in Sweden, I think I touched the brakes twice? Once when coming to a stop at the meeting point for the ride and once to come to a stop at my house. That was honestly it.

So techniques for heavy braking don't really apply here!

[pwa]

This thread has grown arms and legs - quite unexpected!

It's been a very interesting read though. I was out last night on the bike that I used in the UK. But being back home in Sweden, I think I touched the brakes twice? Once when coming to a stop at the meeting point for the ride and once to come to a stop at my house. That was honestly it.

So techniques for heavy braking don't really apply here!

And that is why terrain influences how long wheel rims last on bikes with rim brakes.

[Bmblbzzz]

And why the Dutch can love back-pedal brakes.

[Jon in Sweden]

And that is why terrain influences how long wheel rims last on bikes with rim brakes.

Absolutely. Whilst we actually live in a fairly hilly landscape, the roads here are designed to be driven in winter. Sharp corners, abrupt junctions and steep (more than 8%) inclines are dangerous in winter with full snow cover (even with studded tyres) so there are very few asphalt roads like that.

The gravel is another matter though. Whilst I'd choose rim brakes on the road, discs are needed on gravel.

And in deep snow actually. Rim brakes are absolutely and totally useless in deep snow.

[Biospace]

..it’s the efficiency of disc brakes as brakes which makes them liable to overheat……

Agree or disagree?

Was it you who mentioned an elephant in the room? Both that and your statement above are misleading, any brake's efficiency/ability to transform energy of a moving mass into heat makes it liable to overheating.

Isn't it how a particular brake is specified for its purpose which determines whether or not it's liable to overheat? Drum brakes on motor vehicles developed a reputation for overheating because while engine power, vehicle loads and speeds increased, the increase in size of brake did not keep pace, Pebble mentions this in his last post about 'wagon' brakes.

Disc brakes on a bicycle are perhaps intended more than anything to stop a mountain bike when riding through inches of mud which contaminates the rims. Because they appear to work better in the rain than rim brakes (although not as well as drums) and look smart to most eyes, they're seen as 'good brakes' even for use on tarmac although it's often the invisible hydraulic control which makes them so effective.

[Bmblbzzz]

Disc brakes produce more heat because they're more efficient at converting kinetic energy to thermal energy. If they overheat, it's because they're not dissipating that heat fast enough. Producing heat is an inevitable (and desired) result of friction braking; overheating is not. We should make that distinction.

[Jdsk]

The maximum rate of conversion of energy is obviously central to this, and differs between different types of brakes.

But I wouldn't describe that as efficiency. Efficiency is usually some sort of ratio, and of course in braking systems the relation between applied force at the levers and resultant force at the braking surface is that sort of thing. But maximum rate of conversion of energy isn't.

Jonathan

[Jdsk]

...
The cooling effect of liquid water is good, but the energy requirements for the production of steam are truly exceptional; it takes a lot of energy to heat liquid water from ambient to 100C, but it takes about ten times that amount to turn it into steam. This is why you can be easily scalded by steam, and why if you are wet, you are usually cold, too.
...

My emboldening.

The cooling effect of being wet comes from the loss of insulation by air and the heating of the water and the latent heat of evaporation of the water. Nothing gets to 100°C, and I suspect that the effect of the latent heat of evaporation is greater than that of the bulk heating of the water.

Jonathan

[Biospace]

Disc brakes produce more heat because they're more efficient at converting kinetic energy to thermal energy.
...

Introducing 'efficiency' here can lead to all sorts of confusion and misunderstanding, I qualified how Colin531 was appearing to use the term as "ability to transform energy".

Put simply, disc brakes can be made smaller in diameter than drums for a given amount of reliable effort.

[Bmblbzzz]

Sorry, incorrect term. Perhaps effective would be a better term? Although I think there probably is an element of efficiency in there: disc brakes produce more retardation (and therefore more heat) for a given pressure on the lever.

[Carlton green]

Sorry, incorrect term. Perhaps effective would be a better term? Although I think there probably is an element of efficiency in there: disc brakes produce more retardation (and therefore more heat) for a given pressure on the lever.

As far as I’m concerned your post conveyed the intended meaning. Of course we could all word things a little better and offer more informed comment, however this is a discussion forum not a University Lecture Hall. I could be mistaken but from time to time I sense a degree of pedantry here, that’s unfortunate because such obsessiveness takes away from a discussion forum ….

[Jdsk]

Sorry, incorrect term. Perhaps effective would be a better term? Although I think there probably is an element of efficiency in there: disc brakes produce more retardation (and therefore more heat) for a given pressure on the lever.

As far as I’m concerned your post conveyed the intended meaning. Of course we could all word things a little better and offer more informed comment, however this is a discussion forum not a University Lecture Hall. I could be mistaken but from time to time I sense a degree of pedantry here, that’s unfortunate because such obsessiveness takes away from a discussion forum ….

If you want to describe the physics of braking (or anything else) it's wise to use the common language of physics. That avoids confusion and saves time.

Jonathan

[531colin]

Duplicate

[531colin]

Sorry, incorrect term. Perhaps effective would be a better term? Although I think there probably is an element of efficiency in there: disc brakes produce more retardation (and therefore more heat) for a given pressure on the lever.

Sorry, should I have defined the term “brake”?
As above a brake is a device to retard (in this case) a bicycle. Do I need to define bicycle?
As the function of a brake is to retard the bicycle, a brake which is effective or efficient or just plain old good ; will be good at retarding a bicycle.
And as earlier in the thread, heat will be produced…
As has “ more heat than light” on several occasions.
The amount of heat is proportional to the amount of retardation and independent of the type of brake.

[531colin]

A brake is a brake.
A tandem drag brake won’t lock the wheel.
A disc brake will lock the wheel.
Therefore a disc brake can produce more heat than a drag brake.
I expect somebody will misinterpret that; you can misinterpret anything if you try.