If someone says there is such a thing as internally vs externally vented brake rotors (for cars) - what could they mean?
If you have a rotor formed by 2 plates, the plates separated by an air gap formed by a structural web or matrix or separators, then what additional aspect of their construction would lead to one being called an internally-vented rotor while a second would be called externally vented?
(supposedly for the LH-era 300m there was a difference between the PHP vs non-PHP option package in terms of the front rotors being internally vs externally vented, something that may or may not have any findable authoritative source...)