Brake question

[THR]

Just a small one
but..

Of course big vented discs at the front of the car are most important in most catageries.

but to what extent are they neseccary.
are drums lighter?
how much?
cost?
which has more drag?
less rotational wieght with discs? or more?

if u have anythoughts!

(none about bloody dragsters plz or yanks would be nice)

[Sparky]

Hi THR.

I think the major issue here must be cooling. Big drums tend to give excellent immediate use, ie, without pre-warming, but repeated operation increases temperatures, and hence fade.

Discs, on the other hand, give excellent repeated operation, even during high temperature situations, with the disadvantage that the linings need to be brought up to temp, and that temp maintained, for the discs to work adequately on each application.

I believe weight is a consideration, but a secondary one. A large brake drum has a bigger flywheel effect, and as we know, that is not advantageous in the high-speed world of racing!

Drums need to be substantial to overcome the actuation pressure (ie, outwards and unsupported) while discs, although still needing adequate strength, do not need to be engineered to overcome unsupported actuation, (ie, pads work opposing each other)

Big discs are not so much a search for increased surface swept area (although this is important to a degree), rather the need to position the caliper as far from the hub centre, in order to increase the mechanical advantage.

Drum brakes, with trailing shoe designs, are popular due to the inherent self-servo action. That is, as the shoe is applied to the drum, the rotational forces tend to increase the brake action. Discs have no such self-servo action, but so long as this is recognised before application, vacuum servo systems or increases in master cylinder diameter can overcome this problem.

Discs are typically more expensive to engineer, but are self-adjusting.
They don't suffer as much from increased heat, but do require pad temperatures to be in the operating range before use in anger.
Bigger discs are less weighty than drums, for the same diameter, and I suspect would be somewhat more aerodynamic than any drum capable of offering the same performance.
Linings are easier to replace in discs, although drum linings tend to last longer.

I'd go for discs over drums in most situations.


I'll do a bit more homework, and see what I can come up with...