<VV> Early drums from Z car

[Chris & Bill Strickland]

>... rapidly collected in the mass of the drum or disc then dissipating that
>heat into the air over a period of  time.  Reduction of the mass reduces the
>drum or discs ability to store heat. 
>

maybe "absorb" heat would have been a better description, followed by 
"dissipate" heat -- both cast iron and aluminum are good at it, as can 
be noted by looking at the frying pans on your stove.

Now, by my limited understanding of 'big rig' truck brakes (one 
emergency wheel bearing job and routine service on one or two tractors), 
they would prefer to have the extra metal rather than turn a really ugly 
surface heat cracked drum, so loss of material may be one of the 
considerations on drum turning limits, as it is on disc brakes.

Bill Strickland