Quote:
Originally Posted by vikram_d Why does everbody have the impression that ABS will shorten braking distance. IT WILL NOT. The primary objective of ABS is to give you control over the vehicle during emergency braking. |
Agreed about the primary objective.
However, ABS
does reduce braking distance as well!! (in
most cases).
Provided :
1. It is a well designed/top quality ABS system.
2. The road is dry (no snow/sand/gravel etc).
ABS will however greatly
increase stopping distance on snow/sand/gravel etc.
Quote:
Originally Posted by Sreenivas does that mean the Car (referring to SX4) which has drums on the rear wheels will not be of much use even though it has ABS ? |
Please find your answer / continue the discussion in this thread >
http://www.team-bhp.com/forum/techni...ur-wheels.html Quote:
Originally Posted by ram Braking friction generates heat, causing both braking disks and braking drums to expand.
A hot disk expands towards the brake calliper, causing braking to be more effective.
On the contrary a hot drum expands away from the brake shoes, causing braking to be less effective. This is called brake "fading".
Try it with a Fiat or Ambassador. After a couple of high-speed braking episodes, such as when trying to stop a heavily loaded car going downhill, the brakes will fade!
Besides, disk brake rotors, are also fully and nakedly exposed to outside air. So they are constantly cooled, reducing the tendency to stay oversize. |
Ram,
Interesting explanation, but i feel like you have only touched the tip of the iceberg. Expansion is not really the most significant cause for brake fade, and would only apply if :
- The drums were not self adjusting (all passenger cars w/ drums these days have self adjusting drums (?)).
- The brake shoes were severely worn out as well.
To add to what you said, the cause of (any kind) of brake fade is always heat
(which is generated when friction is used to decelerate the vehicle).
I would say the most commonly experienced cause of brake fade is due to the heat changing the co-efficient of friction of the braking surfaces.
Think of the co-efficient of friction as the amount of frictional force between two materials. eg. sandpaper-on-sandpaper would have a much higher co-efficient of friction than glass-on-glass.
Now, when it comes to brakepads-on-rotor, the coeffieint of friction typically goes up (gets better) just a little as they get warmed up. (This is also the reason why some racing compound pads need to be brought up to temperature before they start working at their best).
However, once the temperature crosses a certain point, the c.o.f begins to drop rapidly. - Meaning the two surfaces have much less friction (stopping power) between them. This is what causes brake fade.
When you use the brakes a lot for continuous periods (eg. going downhill), it generates a lot of heat, which can push the brakepads etc past their ideal operating temperatures - which causes brakefade.
Always use engine braking when possible :
http://www.team-bhp.com/forum/techni...ar-brakes.html
Another cause for brake fade (felt as a spongy pedal) is when the heat from the brakes gets transfered to the brake fluid. This can cause the impurities/humidity/gases in the brake fluid to boil and expand.
Brake fluid in its regular state does not compress easily, and hence is used to transfer pressure from the brake pedal/braking system to the discs very effectively. However, once gasses are present in the brake lines, they can be compressed a little - and hence braking force is not transferred as effectively since the gasses are being compressed as well everytime you press the pedal. This is what causes the "spongy" feel and reduces the effectiveness of the braking system.
You can fix this by doing a brake bleed :
http://www.team-bhp.com/forum/techni...-bleeding.html
Yet another cause for brake fade is the gasses that are liberated from the brake pad itself when they are heated, and hence affect braking. This is called "green fade".
...and after typing all that i found this link which says the same thing probably in a more understandable manner!
Check it out :
HEL Brake Lines - Brake Doctor
cya
R