Forum: bicycles.stackexchange.com
Tags: <brakes><wear>
Title: What is best for your brakes when stopping at the bottom of the hill?
Question: You are at the top of a hill and want to stop at the bottom. What is best for your brakes so you don't wear them down:   brake continuously; or   brake when you reach the bottom?

Answers:
sents: text: In terms of wearing out the brakes, they will wear less when you brake at the bottom.
text: When you descend a hill you have a fixed amount of energy to lose, and when you descend at a higher speed, a larger proportion of that energy is lost to wind resistance.
text: Practically however, brake pads/blocks tend to last a long time and are cheap to replace, wear is not really something to consider too much.
text: It's better to descend safely at a speed you feel comfortable with.
answer_details: author: bicycles.stackexchange.com/users/14027/Andy P
score: 53
sents: text: One should not trade their safety for prolonging brake pads life.
text: Thus gaining the speed and hoping to lose it at the very end of the ride is not the wisest thing to do.
text: Having said that the question is rather whether to: lightly but constantly brake maintaining more or less constant speed; or gain some speed, brake hard, repeat
text: I'd opt for the latter since it allows the rims or discs to cool down thus having them ready and at considerable efficiency
text: should you suddenly need them.
text: Furthermore, you can analyse the evolution of the roller brakes -
text: the latter the generation
text: the larger the radiator for the drum -
text: it was observed that on longer descends when the brakes were partly engaged, they did overheat and lose their braking capability.
text: With larger radiators they did overheat, much later (if ever) though.
answer_details: author: bicycles.stackexchange.com/users/34697/Mike
score: 43
sents: text: There are really two optimal solutions: Go as fast as you dare , perhaps slightly braking, maximize your frontal area (thereby maximizing air resistance) then brake at the end quickly.
text: The idea here is that you are obtaining part of the braking force from air resistance due to the maximized frontal area and maximized speed.
text: Go very, very slowly, braking all the time .
text: The idea here is that the slower you descend, the less the braking power needed is.
text: Power is force times velocity; force stays the same for a given hill, but velocity is something you can affect.
text: Because braking power is lower, the heat dissipation required per unit time is lower, and thus, brake temperature is lower.
text: The interim solution, by continuously braking at an intermediate speed, a speed at which air resistance isn't major braking factor but a speed at which the brakes are heated above the boiling point of water is the problematic strategy.
text: It can cause very fast brake pad wear.
text: Depends on the hill which of there strategies should be used.
text: The problem with the first one is that if the hill is very steep, chances are you may not descend at a speed that would offer good air resistance to dissipate majority of the energy.
text: So, you have to estimate if you dare to choose the first strategy.
text: And remember to use both front and rear brakes so that you have more heat dissipation capacity.
answer_details: author: bicycles.stackexchange.com/users/33932/juhist
score: 17
sents: text: This question is about whether you should execute the bicycle equivalent of a suicide burn.
text: It is faster and more energy-efficient to brake as hard as you can as late as possible than to control your speed early.
text: For a rocket this means sparing fuel, for your brakes this means producing less heat.
text: Do note that the name doesn't come from nowhere.
text: It's too dangerous to depend on your maximum thrust to not slam into an hard object like the Moon at highway speeds, rockets generally do control their rate of descent early on.
text: The other consideration is that your brakes are much better at dissipating when not in contact with the disc, so even if you brake early, it's better to break harder but not continuously.
answer_details: author: bicycles.stackexchange.com/users/39870/Kafein
score: 6
sents: text: Some modern disc brake systems feature special cooling fins to keep the temperatures in check.
text: Greater speeds cause improved flow of air around these fins, thus improving their ability to dissipate heat.
text: Letting your speed grow until you apply the brakes cools them down, whereas constantly applying them a bit would result in constant heat generation without the same cooling benefits.
text: Basically all the heat your brakes generate must be dissipated to the air around your bike, so this applies to brakes without these fins too, although it's far more noticeable with the fins.
text: I recommend braking down whenever you feel you're about to go too fast for your own comfort, then letting go of the brakes for a while and repeating this until you're at the bottom.
answer_details: author: bicycles.stackexchange.com/users/39798/Walto Salonen
score: 1

Summary of the answers:
In terms of wearing out the brakes, they will wear less when you brake at the bottom. Practically however, brake pads/blocks tend to last a long time and are cheap to replace, wear is not really something to consider too much.  It's better to descend safely at a speed you feel comfortable with. One should not trade their safety for prolonging brake pads life.
Keeping the pads touching the rims heats them up from friction and prevents airflow from cooling them down. For this reason, braking at the bottom or once you reach a certain speed would reduce heat and wear. Practically though, brakes are cheap and fairly long lasting, so you should not compromise safety to avoid wear. Modern brakes use cooling fins and are better at dissipating heat, so wear and loss of effectiveness are less of a concern.