Dual Brake Discs

[The Moose]

I was just mulling things over and I was thinking about why no-one (probably most specific to racing to be honest), don't use double brake discs per corner.

If this was viable, would it actually help retard the car quicker, or are the setups available at the moment good enough for there to be no additional benefit?

Also, I guess, it would keep each disc and pad cooler?

[Gibby78]

I'd say rotational mass, spinning up 2 of everything sapps power, probably also weight and width constrictions, I'm not an engineer on these things but that'd be my guess

[Si_steve]

Mainly the space etc would be a problem, then there's the unsprung weight issue.

[havoc]

With regard to rotational mass the moment of inertia would be smaller for 2x small discs than 1x large disc.

However, you'd need 2x calipers, 2x hoses, and some sort of advanced ABS system able to cope.

For a road-car, pretty pointless, even for a supercar. For a race car, you probably don't need to worry due to the light weight of most single-seaters.

[stick100]

i would of thought bigger disk's and better quilty like carbon ceramic would do the job and they wouldn't take up as much room and weigh alot less

[kambites]

havoc said:

With regard to rotational mass the moment of inertia would be smaller for 2x small discs than 1x large disc.

Presumably the opposite is true for braking force, though - that a force applied further from the centre of the hub has greater stopping effect than a force applied near the hub?

[mrmr96]

I think that you'll find that braking force is limited by the grip of the tyres, so twin brake disc setups would not help to slow the car down better.

The reason why high performance/race cars use big brakes is not to increase the peak braking force, but to enable multiple brake applications without overheating the system, and also to enable a greater level of control via pressure modulation. So cooling is important, as it correct selection of pad/disc material and of course brake fluid. High performance cars and race cars are setup to keep their big brakes cool, so they can brake hard time after time.

But the bottom lime is once you have the temp under control, and the level of modulation you need, the tyres are the weakest link and so more discs wouldn't help.

[anonymous-user]

Actually, we already do use "dual" discs! (it's just that they are held apart by thin bits of solid metal (a vented disc! ;-)


(the limitation on brake systems is not one of a maximum brake torque, but one of heat rejection. Simple hydraulics allow us to design a system that applies sufficient clamping force to the pad/disc interface to generate massive brake torques (even with a relatively low Mu(<0.4)), but removing the heat from the disc becomes the limiting factor in a practical system)

[mrmr96]

Max_Torque said:

removing the heat from the disc becomes the limiting factor in a practical system)

I agree with that, but wouldn't you say that once the heat issue is resolved (e.g. ducting etc in race cars) then tyre grip is the main issue?


Think about all the F1 cars you see locking brakes into tight turns... they have plenty of braking force available, but not enough grip.

[Matt UK]

mrmr96 said:

I think that you'll find that braking force is limited by the grip of the tyres, so twin brake disc setups would not help to slow the car down better.

The reason why high performance/race cars use big brakes is not to increase the peak braking force, but to enable multiple brake applications without overheating the system, and also to enable a greater level of control via pressure modulation. So cooling is important, as it correct selection of pad/disc material and of course brake fluid. High performance cars and race cars are setup to keep their big brakes cool, so they can brake hard time after time.

But the bottom lime is once you have the temp under control, and the level of modulation you need, the tyres are the weakest link and so more discs wouldn't help.

Makes perfect sense to me

[seagrey]

Why would you bother?
I would guess that there isnt a car made today that couldn`t lock its wheels with the abs switched off,
if you can lock up the wheels then the system is already over efficient,two discs per corner would just be belt and braces.

The braking force on the wheel would only be as strong as the most efficient of the two calipers on each corner anyway as even with identical calipers there would be slight variations in force according to temp of fluid,temp of pads and discs,friction diferences between discs etc...
There would be no need for a clever abs system either,as they measure wheel speed and regardless of how many discs you had the basic principal wont have changed. just a forked brake pipe at each wheel would be required.

[Gibby78]

Sorry I meant Unsprung Mass, been a long 12 hours in the office, especially on a Sunday

[Tango13]

Ever looked at an aircrafts brakes? They look very similar to a motorcycles clutch except they work in reverse.In terms of braking area they beat anything hands down. The only problem is the amount of heat they generate but this makes for some great you-tube footage so not all bad really

[havoc]

kambites said:

havoc said:

With regard to rotational mass the moment of inertia would be smaller for 2x small discs than 1x large disc.

Presumably the opposite is true for braking force, though - that a force applied further from the centre of the hub has greater stopping effect than a force applied near the hub?

You may well be right...hadn't considered that small detail!

[Willy Nilly]

My company vehicle has multiple brake discs, they run in oil too

[98elise]

mrmr96 said:

I think that you'll find that braking force is limited by the grip of the tyres, so twin brake disc setups would not help to slow the car down better.

The reason why high performance/race cars use big brakes is not to increase the peak braking force, but to enable multiple brake applications without overheating the system, and also to enable a greater level of control via pressure modulation. So cooling is important, as it correct selection of pad/disc material and of course brake fluid. High performance cars and race cars are setup to keep their big brakes cool, so they can brake hard time after time.

But the bottom lime is once you have the temp under control, and the level of modulation you need, the tyres are the weakest link and so more discs wouldn't help.

Well put, once you have enough to lock your tyres you don't need any more stopping power.

[R300will]

Willy Nilly said:

My company vehicle has multiple brake discs, they run in oil too

is it a train?

[The Moose]

98elise said:

mrmr96 said:

I think that you'll find that braking force is limited by the grip of the tyres, so twin brake disc setups would not help to slow the car down better.

The reason why high performance/race cars use big brakes is not to increase the peak braking force, but to enable multiple brake applications without overheating the system, and also to enable a greater level of control via pressure modulation. So cooling is important, as it correct selection of pad/disc material and of course brake fluid. High performance cars and race cars are setup to keep their big brakes cool, so they can brake hard time after time.

But the bottom lime is once you have the temp under control, and the level of modulation you need, the tyres are the weakest link and so more discs wouldn't help.

Well put, once you have enough to lock your tyres you don't need any more stopping power.

But if you could generate oodles of stopping power, would tyre technology then advance inline also??

Just random musings of mine from earlier!!

[PhillipM]

It was tried on bikes a while back, did have the advantage in terms of disc intertia, but the unsprung weight goes up due to the caliper and the pad sandwiched between the two discs tends to overheat long before the outers and ends up wearing unevenly.

[kev b]

Some Rolls-Royce cars have two heavy four pot calipers on one disc, what is the theory behind this as the increase in unsprung weight must be massive?