Ken, I have seen lots of undrilled rotors that are radially vented 
that get the stress cracks as well.
The true be all and end all of brakes are carbon-carbon with 
carbon pads. MUCH lighter than any other functional system but
banned from AMA motorcycle racing due to the cost. The last 
bike systems didn't even have to be heated up like the originals. AP
had a twin disk front end half the weight of iron. BUT 8-10 times the cost.
A motorcycle front end with two calipers, two disks, and two 
sets of pads (which would last the entire season) cost $10,000.00
(a small pause for the gasping people to catch their breath) 
the AMA banned the system not because that didn't work, but rather
because they did and if you didn't have 10K to pony up for 
brakes you weren't going to compete. You also had to change the 600°
brake fluid after each race. More $$$
Enough brake stuff from me! Bill Jepson

 
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