[Harrie]

We are seeing so many people wanting to upgrade their brakes, fix discs at rear etc etc... so i thought may be i'll just share so of my thoughts on this topic. most of it is from information i have read in books or websites over a period of time. so i might be wrong at places also. here goes...

A car travelling at a particular speed comes to rest when we apply the brakes. The brakes (or more specifically the brake callipers) provide a torque which tries to hold the rotating wheels in position. Depending on the amount of friction available between the road and the tire, the car stops or the wheel locks up and drags for a while and stops. Now these are stuff everyone knows.

There are two basic forces acting during braking

1. Frictional force between the tires and road
2. Braking torque supplied by the brakes

The effect of braking:

1. Front wheels lock up - when this happens the car just slides forward we loose steering capablity (of course there is no ABS)
2. Rear wheels lock up - when this happens the rear end starts bouncing all over the place just like applying the hand brakes only

Now let me simplify things further...

Wheels lock up when the frictional force is less than braking torque. Frictional force is not constant at all times.

frictional force = mu * weight acting on the wheels

now suppose weight distribution in a car is 50/50 then when stationary the weight distribution will be same all four wheels. lets say the weight is 100 then the weights on each wheels will be 25

under heavy breaking almost 50% of the weight on the rear is transferred to the front. so now the weights in front will be 37.5 while in the rear it will be 12.5 each

1. Front wheels have more weight acting on them and hence the frictional force is more so they wont lock up as easily.

2. The rear wheels have less weight acting on them and hence they will lock up easily compared to the front wheels.

Suppose you upgrade to rear discs:

The rear braking torque will greatly improve. Now when yuo brake hard, the brakes will lock up even more early and make for a scary moment. So every time you try braking it will be like some one pulling the hand brakes!

Suppose you upgrade the front brakes to ceramics :

In this case we are assuming that the braking torque is increased greatly. What will happen here is that even under severe braking the car will be stable as the front will lock up first and keep the car steady. But the stopping distance would improve as a sliding car loses momentum slowly compared to a rolling one.

Either cases the car will be slow around a track because in the first case it will have heavy over ster while in the second case it will have under steer.

So what is the moral of the story?

Before you go about upgrading the brakes give it a clear thought. Its not always true that a bigger brake would give shorter stopping distances. Instead go for stickier tires. That way you can get better braking without affecting any of the car's handling charecteristics.

Of course another factor i have not considered is the suspension. But maybe i'll put up the effect of the suspension on the car's handling sometime later.

hope this was useful.

[iceman91]

quite true harrie...will definitely break a lot of beliefs about modded brakes....!!

[jigarmuni]

Good write up harrie, but i think... if u are modding ur brakes, its a must to upgrade your tires as well as suspension...!

[Harrie]

Yes jigar i suppose we must upgrade the tires and suspension as well to take care of the brake bias problems. I guess that is necessay to optimize weight transfer and braking.

[jigarmuni]

yeah but i doubt, u can change ur brake bias settings on street cars!! And stiffening the front suspension should help avoid locking up the front brakes...!

[Psycho]

Originally Posted by jigarmuni

yeah but i doubt, u can change ur brake bias settings on street cars!!

The brake bias can be adjusted on the drum brakes but only slightly by using the rear adjuster nut on the brakes by changing the distance of the brakepads to the drum.

However please do not do it yourself as a mis-setting may lead to your rear brakes not working properly when needed, please do go to a good mech to get this done.

And there are a few more techniques of improving the braking capability of a car, I shall list them in the order of benifit:

1) Larger footprint of the tyres (Avoids the wheel from locking up)
2) Brake Pads: Sport Pads are able to improve the resistance on the drums and discs.
3) Better Brake booster (Improves braking response of the car but changes the braking characteristics)
4) A harder front suspension: (about 25 - 50 % stiffer) helps the car to transfer the torque evenly on the front discs and the brakes will work longer without locking up.
5) Grooved Discs: CNC grooved dics also improve frictional rating of the dics but however reduces the life of the brake pads. Good for track racing (especially when it has both grooves and holes for better ventilation)

[Harrie]

Increasing the foot print and the stiffness of the front suspension are better i think. Because the rest might upset the balance of the car. I am trying to find some emprical formulas so i can plot it and maybe arrive at a optimum range. But its proving to be very very elusive. All i am getting is experimental datas. Let me see maybe i can develop it for one particular car.

[Rtech]

Only a switch to rear discs may not decrease the stopping distance, but what it does do is add the ability to modulate them a lot better than drums. Also, in they are more efficient and have better cooling than drums. They disperse with water better as well.

So, all these benefits add up to make discs a far superior choice for a person looking for better overall braking performance.

[RX135]

It still makes sense to upgrade the brakes in case they are providing inadequate breaking resistance. That is why for different vehicles, there are different braking distances for same set of tyres (of course, weight *does* play a big factor here). So, having stickiest tyre may not be the alternative for your car if braking force is not adequate. Basically, both the factors go hand in hand.

[Harrie]

Another factor i have left out is the weight. Strangely it improves braking as well as worsens it. If the weight is more, then the tires can generate more frictional force which can retard the car better wothout locking up the tires.

But a heavier car has got more inertia. So it would take a longer time to come to rest as per newton's law. (is it the 1st or 2nd?)

Funny things cars are. Atleast the physics behind the cars are funny but hey they are all the more interesting!

[Rtech]

The postioning of weight is more important than th actual weight itself. This is why the 911 is so awesome on the brakes!

[jigarmuni]

Originally Posted by Psycho

3) Better Brake booster (Improves braking response of the car but changes the braking characteristics)

Putting a bigger brake booster then the stock one, will make your wheels lock up much more easily.

I think increasing the diameter and thickness of the disc... should also be a good option. Plus a bigger master cylinder, and more of no. of pots for the calliper should do the job well....!

[nitrous]

no. of pots for the calliper should do the job well....!

i think u're referring to the pistons of the brake callipers. i dont think this can be done on most of indian cars other than a few cars for which u have to import these brake sets.

[Edmund]

How easy is it to upgrade the front disc brakes on any car, is it a simple bolt on job if the holes match???
As in the entire unit.....disc, calipers et al....

[drifter]

Its not as simple as it sounds...the entire assembly needs to be changed...however there are upgrade kits available abroad which are car specific. So that makes it a little easier.

Drifter