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.
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.....
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.
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.
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.
Who says you can't change gears in an auto - shit isn't that why they made the t-bar?
I do most of my city driving in 1st, 2nd or 3rd by pushing the t-bar backwards and forwards - you manual drivers should give it a go some time as you're small brain's don't have to remember to push the clutch (just joking guys - please don't kill me). In fact I was doing 100km/hr in 2nd gear @ about 4500 rpm yesterday afternoon just after taking the corner @ 60km/hr (I was being cautious as my rear tyres are starting to 'go-off'). As long as you're prepared for that small gap between the change, you can drive easily as well as a manual. Plus I have the ability of selecting the big 'D' if I get lazy - try that in your manual...
I'm coming up on 27k's on my premium brakes and am told I still got plenty of wear to go. That's better than most of the manual drivers I have read about.
Auto doesn't automatically mean slow and heavy. It's just like all you guys with small dicks would say - it's how you use it that counts....
Jeez I'm acting like a prick today - but a BIG prick.
Can we please have... VENTED DISCS ALL CORNERS!!! Standard!!! PLEASE.. Its dangerous and stupid and primative.. Solid rears.. Very 1980, when it was standard on most sedans. Single piston calipers?
BAII
-Vented front and rear standard across range.
-Twin piston rear calipers..
-Twin pistons at the front well if we must standard, but larger discs, copper plated internal fins
-But optional 4 piston calipers for XR, Ghia.. with reasonable discs, performance pads..
-GT and GT-P, yeh, where are the 6 pots?
Combined with a 100Kg cut from the kerb weight of the BAII and your talking atleast reasonable braking performance..
I look at a BA brakes and then at hatchbacks, japanese or european Sedans.. Hatchback is sporting horizontally opposed 2 piston vented rears.. 80's japanese cars with 4 piston fronts.. its just not right..
Can we please have... VENTED DISCS ALL CORNERS!!! Standard!!! PLEASE.. Its dangerous and stupid and primative.. Solid rears.. Very 1980, when it was standard on most sedans.
Someone's looking in the wrong stable. Although Falcons didn't have rear discs std, those that did have them had vented ones from XB to XF. Ford had the ball, they just dropped it along the way. Holdens only models to have vented rears in this period (to my knowledge)was the VN Grp A .
Can we please have... VENTED DISCS ALL CORNERS!!! Standard!!! PLEASE.. Its dangerous and stupid and primative.. Solid rears.. Very 1980, when it was standard on most sedans. Single piston calipers?
Vented discs are not always the way to go. Engineers need to consider the most likely type of driving expected for a given design. A rotor that runs too cool can be a problem, eg long periods of light use between hard stops. I recall reading about Lotus 49 F1 car (1967) that started with vented discs all-round but they found that they ran just too cold on some circuits! Answer? go back to solid ones....
AP is dead right - Brakes are basically energy converters - Kinetic to heat. Heat required to be dissipated by the braking system is directly proportional to mass and to speed squared. But there is that need for keeping the pad material at optimum temperature as much as possible.
Philbie check out CAPA's website, they have AP racing kits with 6 piston calipers for BA's availible. Dunno wat rotor size but i thuink the kit is about 4 or 5 grand.
ZETECR is correct. Brake pads operate in a temperature RANGE. Having brakes too cold can be worse than those getting too hot. And vice versa. Vented rotors can lead to that "oh my god" feeling when the brake pedal is pushed and the pads aren't up to temp.
Have a look at movitbrakes.com I am putting a set on the Cobra to replace the Brembos. 6pot 380x32mm rotors for the fronts and 2pot 332x32mm rotors on the rear. Wont list my cost. hehe I am paying dealer prices on them.
Holes are cast not drilled unlike Brembo Rotors, DBA Rotors and AP rotors.
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