it has to do with the angle between the point the tire pivots (steers) on and the point the wheel spins on. The steering point needs to be forward of the spinning point to help the car go straight down the road. Think of a shopping carts front wheels (they’re called casters), and how they’ll pivot around with the direction you’re pushing the cart. That angle can be adjusted so the car tracks properly…
I had an '82 Ford Escort. Those things were notorious for lunching the motor if the timing belt ever broke (which they did every 45,000 miles like clockwork) while you were traveling down the road. The valves would stop in whatever position they were in at that instant, and then the momentum of the car would keep the pistons moving up and down, bashing the piston tops in to whichever valves were unlucky enough to still be open, ruining pretty-much everything. At the same time I owned that car, my best friend owned an '82 Chevy Cavalier. We were constantly one-upping each other over who owned the biggest turd…
Back in about '89-'90 I was the assistant manager at a fast oil change place, and we had a regular customer with a maroon '76 Aspen with a bullet-proof slant-six who got his oil changed with us regularly. I could hear him coming. I’d know it was him without even looking because of the distinctive TAP-TAP-TAP -TAP-TAP-TAP-TAP. We’d pull him in and he’d tell us to just change the oil and filter and don’t bother checking all that other stuff, so that’s what we’d do. We’d pull the plug and if more than a half a quart drained out we’d be surprised. After a filter swap, we’d fill it back up and restart it and it would go TAP-TAP-TAP-TAP-tap-tap-tap-ta-ta-ta-t-t-t-t-t-t-t- etc and he’d smile and pay and be on his way. Of course, we’d see him again in about 3 or 4 months, same thing, rinse and repeat. The tapping was his signal to get it changed. Fast forward to '97, after working as a manager at other locations I came back to that same station as the manager there and I’ll be damned if that same guy in that same '76 Aspen didn’t pull in for the same service with that same oil-leaking loud-ass tapping slant-six, still hanging in there…
the over and under-inflation wear isn’t as much of an issue these days as it used to be. In the old days of bias-ply tires, that was definitely the case. You could have a low tire and hardly be able to tell, because the stiff sidewalls would hardly sag. Their flex point was down the middle of the tread. Radial tire construction puts the flex point in the sidewalls, which doesn’t distort the tread as much, plus gives a much smoother ride…