Brad Pitt falls off his Chopper
So Brad Pitt fell off his “chopper” motorcycle. Unfortunately for him as he was in view of the paparazzi.
Hasn’t anyone told him that motorcycles with very high castor angles on the front forks (laid back at an acute angle) have very poor stability at low speeds.
They fall over.
That’s why BMX bicycles and trail bikes have their front forks ALMOST vertical, so they can be manoeuvred at low speeds. If they are vertical, then steering at high speeds becomes very twitchy.
In contrast, high castor angles steer very much in a straight line at higher speeds. Think Peter Fonda (who? say the younger generation) and his “Easy Rider” motor bicycle. Man, was that laid back.
That’s why shopping trolley front wheels always have a small, but positive castor angle on the steering wheels. Otherwise they just jiggle from side to side, and are a pain. Hence why Brad felt!
Your car’s “alignment” incorporates all of the above to keep you safe and in control, and hopefully without the paparazzi.