Hopefull all y'all were taught the tire tread penny check by your fathers. If not, it goes like this: take a penny, and stick it in the channels on of the tire tread, with Lincoln's head pointing down. If the remaining tread is high enough to decapitate the guy let the income tax come into being, or at least kill him by slicing off a chunk of his brainpan, then life is good and your tire has enough tread.
On the other hand, if Mr. Lincoln merely gets a marine hair cut, then it's time to replace your tread. There are more precise methods to define for street legal, but this is an excellent rule of thumb for when it's starting to eat into the margin of safety.
The car now has 4 brand new tires, and it's like getting an upgrade on the entire car. It rides smoother, making a lot of the familiar ruts, cracks, and patches in the road almost unnoticeable. Farm more importantly, it stops faster, accelerates a little better, and the car doesn't dip and sway into turns as much. Now, my "haul two kids, a dog, and two kayaks" sized car will never be a sports car by any means, but it's a wonderful upgrade. Even better, I'm now no longer eyeing wet intersections with the narration in my head going "Will it blend? Or will it hydroplane?"
I shall resist the temptation for a road trip via country roads just to take it on sharp corners, leaving a trail of exhaust and giggles. Really. Maybe.