What does the brake fade percent mean?

[Pringles]

I read the question mark on the braking graph, but it doesn't really explain what brake fade is. Does 10% mean you can only brake 10 times?

[david]

As brakes heat up they lose effectiveness. So 10% fade means they're only 90% efficient - stopping distance increases. :)

[Pringles]

Originally posted by david:

As brakes heat up they lose effectiveness. So 10% fade means they're only 90% efficient - stopping distance increases. :)

So brake fade isn't that the brakes lose efficiency over time?

[david]

Has nothing to do with time, has everything to do with heat. That's why adding brake cooling reduces it. :)

[Admiral Obvious]

The way brakes work is by converting your motion into heat by grabbing the brake disc or drum with a brake pad. However, brakes can only soak up so much heat. When the brake hits a certain point, the brake can't actually apply more heat to the brake disc, and it winds up having the brake pad "floating" over the disc.

Brake fade will usually only happen after repeated, hard, high speed braking, which is the sportiness fade value.

[Pringles]

why does heat make the car go slower??

[Admiral Obvious]

Originally posted by Pringles:

why does heat make the car go slower??

The brake pads grab the brake rotor to slow the car down via friction, which generates heat. When the brakes have too much heat, they'll start to lose performance, which is known as fade.

[Pringles]

So isn't it the friction that slows down the car not the heat?

[Admiral Obvious]

Originally posted by Pringles:

So isn't it the friction that slows down the car not the heat?

Friction generates heat. Too much heat makes it harder to apply friction, so you end up not being able to apply friction and you get worse results out of the brakes.

[david]

Originally posted by Pringles:

So isn't it the friction that slows down the car not the heat?

You are correct. Friction slows the car. Heat doesn't slow the car.

But... as rotors/drums/pads heat up they expand slightly, which gives more friction to a point as there are larger areas of friction. That's why there's optimum temperatures for brakes.

Not enough heat and brakes are slightly less efficient.

Too much heat reduces the brake pads' ability to create the friction necessary to slow the car - that's brake fade. :)

[[CAMSO] MrChips]

Originally posted by david:

Originally posted by Pringles:

So isn't it the friction that slows down the car not the heat?

You are correct. Friction slows the car. Heat doesn't slow the car.

But... as rotors/drums/pads heat up they expand slightly, which gives more friction to a point as there are larger areas of friction. That's why there's optimum temperatures for brakes.

Not enough heat and brakes are slightly less efficient.

Too much heat reduces the brake pads' ability to create the friction necessary to slow the car - that's brake fade. :)

In the case of drum brakes, too much heat causes the drums to expand too much, and then you can't generate the clamping force necessary to stop the car anymore. Hence why disc brakes are superior in nearly all passenger car applications.

Also, if you really want to get into the nitty-gritty of the physics, when you apply the brakes, so much heat is generated at a microscopic level that the brake pads/shoes actually transition from solid to gas. A little bit is fine - normal, even - but if the pads and rotors/drums are too hot, then too much gas forms at the friction interface and it causes the pads/shoes to float, which again reduces clamping force.

[Zeivo]

Originally posted by CAMSO MrChips:

Originally posted by david:

You are correct. Friction slows the car. Heat doesn't slow the car.

But... as rotors/drums/pads heat up they expand slightly, which gives more friction to a point as there are larger areas of friction. That's why there's optimum temperatures for brakes.

Not enough heat and brakes are slightly less efficient.

Too much heat reduces the brake pads' ability to create the friction necessary to slow the car - that's brake fade. :)

In the case of drum brakes, too much heat causes the drums to expand too much, and then you can't generate the clamping force necessary to stop the car anymore. Hence why disc brakes are superior in nearly all passenger car applications.

Also, if you really want to get into the nitty-gritty of the physics, when you apply the brakes, so much heat is generated at a microscopic level that the brake pads/shoes actually transition from solid to gas. A little bit is fine - normal, even - but if the pads and rotors/drums are too hot, then too much gas forms at the friction interface and it causes the pads/shoes to float, which again reduces clamping force.

This is a great explanation, I was literally about to get on today and spend 10 minutes typing somthing almost exactly like this
Thanks chips :D

[david]

Originally posted by CAMSO MrChips:

Also, if you really want to get into the nitty-gritty of the physics...

I kept my responses to what "brake fade" refers to in the game.

If we really wanted to get into the nitty gritty, overheating brakes can lead to "pad fade" (this is the only time I've heard it referred to as "brake fade"), as well as cracked rotors and brake fluid boil.

Hopefully Pringles now has a clear understanding of what the game is referencing. :)

[Pringles]

So 10% brake fade isn't that bad? If the brakes are working at 90% efficiency, that's still better than brakes with 0% brake fade that are weaker, am I getting that right?

[Zeivo]

Originally posted by Pringles:

So 10% brake fade isn't that bad? If the brakes are working at 90% efficiency, that's still better than brakes with 0% brake fade that are weaker, am I getting that right?

yes, well done
most cars like cheap ones for example the ford ka, c max s max mazda mitsubishi and toyotas these days and even before had a brake fade like this
so ya it aint bad
unless its a rich car

[CBR JGWRR]

Originally posted by Pringles:

So 10% brake fade isn't that bad? If the brakes are working at 90% efficiency, that's still better than brakes with 0% brake fade that are weaker, am I getting that right?

Depends.

On a racing/track/super/hyper/sports car, where repeated braking from high speed is a reasonable sequence of events, 10% brake fade is something that would absolutely affect the driver and the vehicle and could well lead to insufficient braking availability in the event of a potential crash at speed.

On a normal, sensibly driven road car, where only an absolute idiot drives in such a way that they need to do multiple emergency stops and 10% brake fade is extremely unlikely to be noticed outside of specifically conducted testing for it. (this is because the vehicle's kinetic energy increases with the square of the velocity, and therefore means one 100 mph to 0 stop, and four 50 mph to 0 stops, put roughly equal amounts of energy into the braking system; the latter is slightly less because of having a small amount of time to cool from re-accelerating to 50 mph each time)