How Do Brakes Work? The Science of Stopping

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If you’ve ever wondered just how mountain bike brakes work but been too afraid to ask, this video might just bring you some answers.

Although it’s from SRAM, it’s not telling you to go and buy their brakes. Instead, it’s telling you that the brake that will be best for you depends on a whole variety of factors. Riding trails? You want trail brakes… right? Nope. Apparently it matters how fast you’re riding, how heavy you are, how often you ride… and a whole lot more.

Should you have mineral oil, or DOT fluid? Well, that depends too. There are no simple answers, but there’s a whole lot of science and information packed into this short video.

Your first task is to watch it.

And of course, your second task is to head to the comments section and regale us with tales of why it’s wrong, you’re right, and your own personal recommendations for which brakes work best for you and so will of course work perfectly well for the rest of us. Got it?

And your third task is to check out the colour of your rotors. Are you in camp brown, or camp rainbow? No idea what we’re talking about? Watch the video and all will become clear!

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Hannah Dobson

Managing Editor

I came to Singletrack having decided there must be more to life than meetings. I like all bikes, but especially unusual ones. More than bikes, I like what bikes do. I think that they link people and places; that cycling creates a connection between us and our environment; bikes create communities; deliver freedom; bring joy; and improve fitness. They're environmentally friendly and create friendly environments. I try to write about all these things in the hope that others might discover the joy of bikes too.

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  • How Do Brakes Work? The Science of Stopping
  • BruceWee
    Full Member

    If moisture could pass through the joints and seals to get into the system when there is no pressure differential, fluid would squirt out when you applied the brakes. This doesn’t happen because the system is sealed.

    There are microscopic holes in all the seals. You have to remember that DOT fluid is hygroscopic and actually attracts water.

    Often a seal only seals properly when it’s under pressure so it’s entirely possible that the brakes won’t leak but can still absorb moisture.

    According to your logic there is no need to ever change brake fluid. Do you ever change your brake fluid? Why?

    Posted 2 years ago
    Olly
    Free Member

    My very first Hope brake had an adjuster on the top of the reservoir. Even when they were brand new they would lock on if left in the sun and you had to back off the adjuster to be able to ride the bike again.

    C2s, the C being for Closed. (i believe)

    In a closed system, the reservoir feeds the hose further down the valve, so when you pull on the lever, the reservoir itself is also under pressure. There is a plunger under the adjuster that pushes the fluid up and down exactly as the plunger on the lever does.

    On a modern Open system, (i think) the oil reservoir port is positioned so that as you pull the lever, the reservoir is seperated from the pressurised brake system, and is never under pressure itself. As you release the brake the port opens, and the fluid can equalise its pressure/volume with the reservoir, which is open to atmospheric pressuire (save for a diapram that just keeps the air our the fluid and the fluid in the reservoir) to compensate for pad wear and also heating.

    [edit]

    Brake systems are highly pressurized when you clamp on the brakes. The fluid on the inside is at much greater pressure than the air on the outside. If moisture could pass through the joints and seals to get into the system when there is no pressure differential, fluid would squirt out when you applied the brakes. This doesn’t happen because the system is sealed.

    only down stream of the lever. the reservoir doesnt pressurise, and is effectively open to atmosphere. The diaphram only keeps the fluid in the right place, but wont stop moisture getting in the fluid.

    Posted 2 years ago
    thols2
    Full Member

    The diaphram only keeps the fluid in the right place, but wont stop moisture getting in the fluid.

    It seals the fluid from the atmosphere. Moisture can’t get in unless the diaphram is damaged.

    Posted 2 years ago
    BruceWee
    Full Member

    only down stream of the lever. the reservoir doesnt pressurise, and is effectively open to atmosphere. The diaphram only keeps the fluid in the right place, but wont stop moisture getting in the fluid.

    That makes a lot of sense actually.

    I’ve found that if the fluid has expanded so that the reservoir is effectively overfilled and I try to push the pads back to get the bleed block in the fluid is actually pushed out past the seal.

    At the time I remember wondering how it was able to withstand the pressure of the braking system so your explanation clears that up.

    Posted 2 years ago
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