{"id":9658,"date":"2019-07-02T09:05:59","date_gmt":"2019-07-01T23:05:59","guid":{"rendered":"https:\/\/www.privatefleet.com.au\/blog\/?p=9658"},"modified":"2020-06-20T00:10:51","modified_gmt":"2020-06-19T14:10:51","slug":"give-me-a-brake","status":"publish","type":"post","link":"https:\/\/www.privatefleet.com.au\/blog\/blog\/give-me-a-brake\/","title":{"rendered":"Give Me A Brake"},"content":{"rendered":"

\"\"Imagine that you\u2019re driving along a typical suburban street.\u00a0 A movement to the side catches your eye and you spot somebody\u2019s dog off the leash madly rushing full tilt down a driveway, barking madly at the cat across the road.\u00a0 Next thing you know, Doggo is rushing into the road.\u00a0 Without thinking, your right foot darts off the accelerator and hard onto the brake.\u00a0 Your car screeches to a standstill, stopping short of that lunatic of a dog and shoving you hard against your seatbelt.\u00a0 You growl something about idiotic animals and people who can\u2019t control their dogs, then keep on going, barely thinking about the mechanical miracle that has just taken place.<\/p>\n

Brakes. We take them for granted, especially after we\u2019ve been driving for a few years.\u00a0 However, they are super-important for safety.\u00a0 Imagine what it would be like without them.\u00a0 You might have had a small taste of this sort of thing as a child if you screamed downhill on a scooter or skateboard (or, in my case, a bike with worn-out brake pads) \u2013 that feeling of being out of control and knowing that gravity will accelerate you faster and that there\u2019s no way of checking or slowing that thing down.<\/p>\n

Needless to say, brakes pre-date cars.\u00a0 Steam trains needed them and so did stagecoaches, and the basic principle behind all brakes is the same.\u00a0 The vehicle is moving because the wheels are turning, so to stop it moving or to slow that motion down, one needs to slow the wheels down. This is done by clamping something large and hard onto the wheel, which produces friction that soaks up the kinetic energy of the wheels. And this is the first and most important mechanical principle behind any brake: friction.\u00a0 The bigger the surface area applied to the turning wheels and the more force it\u2019s applied with, the more quickly the turning stops.<\/p>\n

In your car, the friction is applied by disc brakes, which have been around since Citro\u00ebn put them on mass produced cars in 1955.\u00a0 Disc brakes consist of a metal disc that\u2019s incorporated into the wheel. You can have a powerful pair of callipers that grab this disc as it spins and slow the turning that way.\u00a0 You can think of it as a more sophisticated adaptation of your old bike brakes: instead of grabbing the whole rim, it grabs something near the centre. The callipers are fitted with brake pads that are usually made of tough rubber, which absorbs heaps of force and can handle heat \u2013 and you need to make sure that you replace your brake pads on a regular basis, as they do wear out over time and you\u2019re sunk without them.\u00a0 You\u2019ve also got drum brakes (or disc and drum), where a stationary disk covered with an energy absorbing lining, known as a shoe, presses against the disc, applying the necessary friction.<\/p>\n

A lot of kinetic energy and a lot of momentum are involved in a moving car.\u00a0 However, it takes the subtlest bit of pressure to slow a vehicle from, say, 100 km\/h to 85 km\/h as you approach a corner.\u00a0 If your average mid-sized sedan has a mass of 1600 kg and the equation for velocity is K = (m \u00d7 v2<\/sup>)\/2\u2026 you\u2019ll have gone from 617.83 kilojoules to 445.98 kilojoules or a difference of 171 kJ.\u00a0 This is equivalent to roughly the energy expended by a petite woman doing slow dancing for quarter of an hour\u2026 and you sure didn\u2019t apply that much with that little twitch of your foot. Obviously, something\u2019s happened to amplify what your feet and legs did or the car wouldn\u2019t have responded one iota.<\/p>\n

The next mechanical principle that kicks in is the one discovered by Archimedes and I don\u2019t mean the one that saw him running through the streets in the nude shouting \u201cEureka!\u201d after his bathtub overflowed.\u00a0 I mean the \u201cGive me a long enough lever and a firm place to stand, and I can move the world.\u201d In other words, the lever principle. One tiny movement on the short end leads to a lot of movement on the long end.\u00a0 This is certainly at play in your brake system but amplification comes in the form of fluid courtesy of the principles of hydraulics.\u00a0 Don\u2019t make me go into the equations for hydraulics, as that\u2019s university-level physics and I didn\u2019t study that.<\/p>\n

Fluids can\u2019t be squashed, which is how water pistols work. Actually, a water pistol is a good place to start understanding the principles of hydraulics. You couldn\u2019t throw water with one finger very far or with much force, but by applying pressure to that water, you can get quite a bit of water going a fair distance, preferably onto your big brother\u2019s face.\u00a0 The main force goes from your brake pedal to the master cylinder, which converts the force of your foot into hydraulic pressure, like your finger on the trigger of a water pistol.\u00a0 The brake fluid then exerts pressure on the slave cylinders (one for each wheel that has the brakes) and the slaves apply the brake drum or the callipers, and everything kicks in to slow the vehicle down.<\/p>\n

There are a lot of moving parts involved and naturally, given the nature of things, the business end of the brake will wear out over time.\u00a0 And they will need to be replaced, so you really don\u2019t want to try cheating or skipping on this important part of car maintenance.<\/p>\n

If, for whatever reason, you\u2019re in the scary situation where any of these systems fails, here\u2019s what you do:
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