Unless i misread this the swept area of a disk brake is always larger than a drum:
http://books.google.com/books?id=5rW...sult#PPA184,M1

Perhaps I've unintentionally mixed up what i was trying to say. To restate differently, Drums are less efficient so they need more applied energy to accomplish the same amount of work as a disk was the thought I was trying to convey.

 

Two completely different effects with differing efficiencies.

Swept area has more to do with heat flow into and out of the rotor, and has little or no effect on the force required to get that job done, assuming that fade is not present.

Drums are less efficient at heat dissipation, but more efficient at transforming brake line pressure into actual stopping (again assuming that fade is not present). Figure 7.2 in your link explains this, where the friction developed by one drum brake shoe adds to the force applied to the other shoe. IOW, you the driver are getting some help from the brake shoe geometry. This effect is not present in any current disc brake design. This also explains why drum brakes are somewhat more sensitive to fade - once the primary shoe friction shoe starts to drop off so does the apply force to the secondary shoe (whose friction is also dropping, so you lose twice there).


Norm

 

Thank you for your comments Norm, for the majority I am in agreement. However, I don't totally agree with your assumptions based on my experiences with drum brake systems over the years. This, mainly due to fade (either mechanical and/or lining) is an inherent issue with all brake systems and these Mustang small shoe/ drum area installations can only dissipate so much of the energy produced. As we all know a disk set up works much better due to it's less susceptibility to heat induced fade which translates to more efficient energy dissipation.

Thus, it takes more "foot" to get the same level of braking in a classic car (if that's even possible) that we as modern car operators have come to expect in respect to the modern disk brakes our cars have.
(this was the original point i was after)

 

I think we're getting to the point where we'd need to have a whole lot more information available. The need for more "foot" is also dependent on things like drum ID (vs mean disc brake pad radius), tire size, master and wheel cylinder sizes, friction coefficients, and pedal ratios. Believe me, I know that 1960's drums were nothing to write home about even on the first hard stop. I also know that early nonpower disc brakes tended to require even more pedal force in "subcompact" cars that were well over 1000 lbs lighter than the drum-braked "intermediates" (though you did have far better feel and ability to modulate them).

At this point in time it's almost academic, as whatever FMVSS deals with brake system performance sets a maximum pedal effort for a specified deceleration. Old, small-diameter drum brakes would almost certainly not pass muster, nor would nonpower discs in any but the lightest weight vehicles (which we really don't have any more other than those from Lotus - and even those weigh ~2000 lbs). In this respect, we've all gotten spoiled by the minimal physical effort required.


Norm