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Should brake discs get hot?

Kwik Fit | Friday 2nd August 2019 12:14pm

car tyre with the brake rotor on the inside and red brake calipers

Your car’s brakes work by converting kinetic energy (the motion of your wheels) into heat so that your vehicle can safely come to a stop. This means that it’s completely natural for brakes to get hot in order to stop your vehicle.

But when do hot brakes become dangerous? We’ve answered this question and more in this helpful article. Read on to find out what hot brakes can do to your vehicle.

How do car brakes work?

Before we can think about how hot our vehicle’s brake discs get, we need to understand how the brakes work.

To slow your vehicle down, you press down on the brake pedal. When you do this, brake fluid travels to your brake calipers. The harder you press the brake, the more fluid is applied to your brakes. This is called hydraulic force multiplication.

After this, the brake pads that are positioned either side of the brake disc, or rotor, will squeeze together, trapping the rotating brake disc in the middle. As the brake pads close around the rotor, they slow it down, causing your car to decelerate. It is this action that causes a lot of friction. Friction produces heat, which is why your brake discs may become hot after braking for a prolonged period of time.

It takes a lot of pressure to stop a one tonne vehicle. This is why you need to keep your brakes maintained and ensure that they're working properly, otherwise you could cause a serious accident.

How hot should brake discs get?

Now we’ve determined that it’s okay for your brake discs to get a little bit hot, but what’s the maximum temperature they can reach while continuing to work safely?

For standard road cars, you should expect your brake discs to reach around 130°C. The brake discs on track cars can reach around 500°C, but these vehicles are built so they can cope with such an extreme temperature.

If you’re frequently braking, without allowing time for your brakes to cool back down, you could experience brake fade.

What is brake fade?

Brake fade can occur as a result of excessive braking, which is why it’s so important to keep your brakes as cool as possible. Below, we’ve outlined the types of brake fade you may experience and how you may be able to prevent each one from occurring.

Friction fade

This is the most common cause of brake fade. Your brake pads can create a lot of friction and heat when they’re working to slow your car down. If you are continuously applying the brakes, and creating more heat, you aren’t enabling any time for the brakes to cool down before they’re applied again. For example, if you’re driving down a long hill you may be tempted to gently apply the brakes to slow down your vehicle. Instead, it’s more beneficial to apply the brakes firmly for just a few seconds to get your speed down, and then use your gears to slow the engine down.

When you put your foot on the brake pedal, you should apply the brakes for a few seconds before taking your foot back off. This method will reduce the chance of friction fade.

If you’re already experiencing friction fade, you’ll need to allow the brakes to completely cool for at least an hour before you drive the car again.

Brake fluid fade

Most car manufacturers advise that you change your brake fluid periodically. If you don’t change your brake fluid, it can degrade and begin to absorb water. This excess water can cause the brake fluid to boil, which will produce steam. The brakes may begin to feel spongy and could even stop working.

You should have your brake fluid changed at least every couple of years.

How to tell if brake discs need replacing

If your brake discs have been subjected to excess heat, they may need replacing altogether. Brake rotors can begin to warp if you don’t allow your brakes to cool down correctly. The rotor should have a flat surface so that the brake pads can keep in contact with it at all times. If the rotor is warped, you may feel a movement in the brake pedal or the vehicle might jerk as it comes to a stop.

You may also be able to tell if a rotor has overheated by looking at it. The surface could be discoloured or it could be a blue or purple colour. This discolouration can cause the surface to harden and means the brake pads may not work properly to slow the rotor down. This might make your vehicle come to a stop much slower than it should, which could be dangerous.

Always be careful when looking at your brakes. If you’re checking your car’s brake discs, you should make sure that they have had ample time to cool down. If you touch the surface when it’s still hot, it could burn you.

mechanic changing a disc rotor in a garage

How to cool hot brakes

Hot brakes shouldn’t be something to worry about unless you experience any of the following:

  • Vibration in the pedal when you apply the brake
  • Squealing or screeching noise when you apply the brake
  • A burning smell
  • Smoke coming from the tyres
  • Spongy/soft brakes

If you think your brakes are overheating, there are a few ways you can try to cool them down while you’re on the road.

First, you should try to avoid overusing the brakes. Always look ahead of you for hazards so that you can see them more quickly and bring your car to a stop without slamming on the pedals.

As previously mentioned, be mindful when you’re going downhill that you aren’t constantly applying pressure to the brake pedal. You should allow your brakes to cool down in between uses.

You could try engine braking. You shouldn’t do this all the time, but it can be a useful technique if you think your brakes are overheating. You should downshift the gears, moving down from one gear to another, allowing your revs to increase but keeping your foot off the accelerator so the car is continuing to slow down. This way of coming to a stop can be slower than applying the brakes, so make sure you have plenty of room in front of you to decelerate this way.

For track cars, you can have brake ducts installed. These work by channelling air directly to the brake disc as you drive. This air is much cooler than the brakes and the airflow helps to move the hot air away. This allows the brakes to get rid of the heat at a much faster rate, and it alters the average temperature of the brakes. Without a brake duct, this hot air finds it hard to escape from the brake disc.

Tags : Brakes

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