Why drums in rear and discs in front ?

[abhaybakshi]

A small query...why Indian car manufacturers provide drums at rear tyres and discs in front ?

Why can't they provide discs on all four ?? or is there any other reason ?
(I guess cost)

[Zappo]

Well, actually cost is a big reason for this setup. However having said that this setup is mostly adequate for most of the everyday use cars. Anyhow most of the modern cars drive the front wheels. The rear wheels are only pulled. So if the front wheels have a good braking setup (perforated/ventilated discs) this proves adequate along with a good drum setup at the rear.

Read the edmunds article on the same.

[CrAzY dRiVeR]

Also, on braking... The main component of vehicle weight acts on the front wheels, and only a small component of it acts on the rear wheels

In simpler words, weight gets concentrated towards front due to the inertia of the vehicle

So... We need better braking at the front...

Even in cases where both discs are provided, the front brakes will be a disc of bigger dia, than the rear ones...

[theMAG]

Cost. C+/D segments and above have discs all-around.

[condor]

Originally Posted by Zappo

Anyhow most of the modern cars drive the front wheels. The rear wheels are only pulled.

Zappo, are you sure about this? If I were to extend this logic, then RWD vehicles would have discs at the rear and drums at the front.

The same edmunds article gives a good explaination to Abhay's question: "Combined with the fact that between 60 and 90 percent of a vehicle's stopping power comes from the front wheels, it's clear that a well-designed, modern drum brake is all that's required for most rear wheel brake duty"

[Zappo]

Hmmm... but why is it that 60 to 90% of the stopping power comes from the front? Probably one of the reasons is that if the "driven" wheels are stopped adequately the rear wheels which anyhow do not have a power of their own are easier to stop. Of course another big reason could be the inertia thing. With the engine and other components being there at the front the inertia starts generating from the front. That is where you need the max stopping power, as pointed out by CD.

[sharathjeppu]

Does the ABS work differently if the rear has a disc brake vis-a-vis a drum brake? I was always curious about this.

[revtech]

i guess it would work the same way.intention being to prevent locking.

[Rehaan]

Originally Posted by sharathjeppu

Does the ABS work differently if the rear has a disc brake vis-a-vis a drum brake? I was always curious about this.

I seem to be under the impression that it is not possible to have 4-wheel ABS if you have drums at the rear..... (true?)

cya
R

[Desert fox]

ALSO helps the vehicle in deparment of the mechanicaly operated handbrake. Modern(er) 4-disc brake cars come with drums co-existing with the rear discs.

[rocksterraghu]

Now it's time for me to express my opinions and understandings.

* Think about it this way, on a RWD, if you pull the hand brakes while the car is still in motion, would it still spin the car? That should answer one question. Having the car in motion and applying harder brakes on the rear wheels is never a good idea, regardless of the type of vehicle.

* Regarding ABS, it shouldn't really matter. The ABS just lets the wheel rotate when there is a slippery surface where the chances of the car sliding are higher when they're not rotated. So, what technology is involved to stop the wheels from rotating is out of question.

Disagree with me? Please go ahead and correct me.

[condor]

Zappo, more than driven wheels, doesnt it make more sense when we consider the direction of motion? The inertia is also in the direction of motion, and it's more effective to stop it there than holding the vehicle back, from the rear end.

[WhiteKnight]

Originally Posted by condor

doesnt it make more sense when we consider the direction of motion? The inertia is also in the direction of motion, and it's more effective to stop it there than holding the vehicle back, from the rear end.

Spot on!! Add to it the weight trasfer. In case of deceleration, weight is transfered to the front, meaning less grip at rear. So a brake biased to rear would only help locking up the rear.

[vid6639]

Exactly whiteknight it's due to the weight transfer.

Try going in reverse and pull the handbrake, you will notice the brakes will not lock. Why? because the weight transfer goes to the rear giving more inertia and the brakes need more force to stop the car.

it does not make difference whether RWD or FWD or even if the car's front engined or rear engined.

Even in a rear engined RWD the braking force will be more for the fronts than the rears.

[adya33]

Originally Posted by Rehaan

I seem to be under the impression that it is not possible to have 4-wheel ABS if you have drums at the rear..... (true?)

cya
R

Yup. Incase of cars with rear drum breaks the ABS module is only connected to front wheels.

Also having disc breaks to all 4 wheels without ABS is a suicide. The car will lockup more often than car with drums in rear.
This is the reason all cars with disc breaks all around come with ABS.