>>1263716Okay, so, conical wheels have problems at higher speeds where their self-correcting nature behins to overcompensate and instead shakes back and forth, causing track damage and (possibly) leading to derailment. This is what's know as hunting oscillations. The faster you go and/or the more cone-shaped the wheel profile is, the worse it gets. Because of this, most high-speed trains have wheel profiles that are almost completely flat.
The BART engineers, for whatever reason, were concerned about the stability of their trains at high speeds. Perhaps they thought they'd be running at triple-digit speeds that never actually materialized. Whatever their reasoning, they thought keeping the trains stable at high speeds was vital. This is why the broad gauage and wheel profile were chosen. A broad gauage would be inherently more stable than a narrower one, and a cylindrical wheel profile would be more stable at high speeds.
These were really dumb decisions. The legendary noise and track problems of the system system from the BART engineers that didn't consider that flat wheels on flat wheels rounding corners would be guided soley by the wheel flanges. That's why the system is so noisy: the trains screech and squeal as the wheel flanges grind against the rail, because unlike more conical train wheels, there's no "self-steering" effect.
