1/8/2024 0 Comments Anti lock braking system pumpABS won’t help with that – but that’s where Electronic Stability Control comes in. There’s also the potential for tyres to slip sideways if cornering too fast. That rapid bursting is what makes the characteristic ABS crunching noise.ĪBS just controls the ‘straight line’ action of the tyres on the road, but that was sufficient for my purposes yesterday. It’s like what you need to do on a non-ABS car (probably there aren’t too many of these on the roads any more) – pump the brake pedal yourself. It allows the braking to take full effect, but then releases the brakes momentarily when they ‘lock’, before applying the braking again. The ABS senses when the wheels have locked, and then pumps brake fluid in bursts. You will take longer to stop with sliding tyres than with rolling tyres. But also, since the coefficient of kinetic (or ‘sliding’) friction is generally less than the coefficient of static friction ( EngineeringToolbox gives about 0.5-0.8 for rubber against dry asphalt), it means that the total braking force is lower. First it means that you have lost control of the car, and it doesn’t do your tyres any good. If the braking on a moving car is too severe, the frictional force between the road and the tyre is insufficient to keep the tyre sticking to the road, and thus ‘rolling’. However, there is a limit to that frictional force, and this is why wheels can lock and cars slide, especially on a wet, icy or loose-surface road. The frictional force between the road and the tyres is sufficient to prevent the car from sliding backwards down the hill. It also means that, by applying the handbrake and locking the wheels, the car can park happily on some very steep gradients, provided it’s not icy. The bit of the tyre in contact with the ground is always stationary with respect to the ground. Rubber against dry asphalt has a high coefficient of static friction (a measure of stickiness between surfaces) – EngineeringToolbox gives it as about 0.9 – which means that when a car is moving forward the tyres are rolling, not sliding, along the road. Braking ultimately depends on how good your tyre’s grip with the road is.
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