Why Late Model Cars Need Bigger Brakes (BA Falcon) - Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars

Aussie Pete · 05-19-2003, 16:25

Some numbers to show you why late model cars need better brakes than those of earlier years. You have to remember that the brakes on cars today are handling much bigger levels of energy.

I have assumed the energy absorbed by the brakes is the entire amount of kinetic energy lost while slowing down (not quite true). Also, kinetic energy is one half mass times velocity squared.

Take a stop from 100km/h (27.8m/s):

1200kg car; E = 1/2 x 1200 x 27.8^2 = 463700 J
1800kg car; E = 1/2 x 1800 x 27.8^2 = 695550 J (1.5 times the energy)

However, consider that the cars today are generally capable of much higher speeds and accelerate better between two points and the issue becomes even worse:

1200kg car at 80km/h (22.2m/s); E = 295700 J
1800kg car at 100km/h; E = 695550 J (2.35 times the energy)

Now the big eye opener. Let's say you're on a winding road. You make repeated applications on the brakes to slow down for corners. In this case we assume the newer car accelerates better and handles better.

1200kg car cornering at 70km/h and accelerating to 100km/h

E = 1/2 x 1200 x 27.8^2 - 1/2 x 1200 x 19.5^2 = 463700 - 228150 = 235550 J

1800kg car cornering at 80km/h and accelerating to 120km/h

E = 1/2 x 1800 x 33.3^2 - 1/2 x 1800 x 22.2^2 = 998000 - 443550 = 554450 J (2.35 times the energy EVERY corner)

Now you see why the issue just gets bigger and bigger as cars get better and heavier.

KenOath · 05-19-2003, 17:07

You bored AP?

AusXH · 05-19-2003, 19:14

/me thinks he's trying to justify them huge arse Brembo's :s6:

Aussie Pete · 05-19-2003, 22:58

Nah, some people were saying how older cars never seemed to have brake shudder etc.

ford.boy · 05-19-2003, 23:07

Ahh, yr ten science is good for something.

FTEfan · 05-20-2003, 02:11

Older cars would be hard pressed to generate enough heat in the brakes due to the speed and constant stopping.

smciner1 · 05-20-2003, 02:13

I have noticed that aerodynamics plays it part at highway speeds. Lift off the throttle at 100 km/h in my EF XR6 and it takes forever to loose some speed.

Do the same in my XB GT and it slows down a lot quicker.
so while improved aerodynamics helps late model cars in acceleration, fuel economy and wind noise, there is a (small) down side to it.

As an interesting thought to this, my EF XR6 and XB GT have very similar sized rotors, but the XB has vented rear disks standard, something that is a $6,000-00 option on a new GT. Just food for thought.

P.S. Thanks for the brush up on the Physics lesson AP.....

WBT56 · 05-20-2003, 02:35

Another issue is that most injected engines hold the revs up a little while coasting, and this means that you are on the brakes more to keep to the in town limit. I know a bloke who had two identical cars, except one was an auto and one was a manual. The auto used 3 times the brake pads of the manual.

JC-XR8 · 05-20-2003, 05:45

That's because in a manual you change down through the gears (manually) which 'engages' engine braking. An auto changes down (automatically) as it hits certain speeds and has little or no engine braking effect. Unless, of course, you change the auto down manually to help with engine braking.

WBT56 · 05-21-2003, 01:48

It's more than that. The engine in either case does not return to base idle with no throttle- the idle stays high. Disconnect your VSS in an injected manual and go for a drive. The engine braking is greatly increased when the PCM thinks the car is stationary.