Disc vs Drum

[Steve Stegmann <stegmann@domain.elided>]

There is a lot of confusion about disc vs drum.

1-  There is *no* difference in sheer power.

2-  Drums fade seriously faster in heavy service, especially repeated 
stops with no cool down period.  The friction surface moves away from the 
shoe as it heats up.  As race cars were switching over in the 50's and 
60's it was no contest after the first few laps.  Ferrari persisted with 
the drum brakes, only proven technology need apply.  They were some of 
the prettiest and most amazing aluminum castings but there was no hope, 
they switched.

3- Discs are more controllable, less "grabby".  Disc response to pedal
pressure is linear, while drums are non-linear due to the self amplifying
design.  You can make non-amplifying drums but nobody does for cars, all 
are "leading shoe" designs.  Leading-shoe means one of the shoes is self 
amplifying.  A trailing shoe design is non-amplifying.  I had twin 
leading shoe design on my '73 Toyota.  Killer grabbing.  Plenty power, 
too light pedal, but uncontrollable in an emergency.
There are all kinds of non-amplifying industrial drum brakes, they work 
great.

Sorry 'bout the bandwidth

STeve

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Steven A. Stegmann
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