Eventually, you will notice that your car is losing traction due to tread loss, especially on wet surfaces. You'll also notice that you may not be getting the mileage out of your car that you used to. A good, simple way to check the tread is with a quarter. On most tires, when the tread is lower than Washington's nose, it's time to take your car in and see of you need new tires.
There are tread wear indicators that are in the tire itself. When the tires need to be repalced theese indicators show.
new tires. If the tires brake, you'll need it
We would need to Know WHICH Saturn and make and size of tire. The pressure is the same whether they are new or old tires.
A certain speeds, your steering wheel starts to shake.
When your tires have 2/32" tread depth left you need to replace them.
Yes, they are just lower profile tires.
Yes
when they are no longer balanced.
No the rims do not need to be replaced along with the new tires unless certain conditions require you to do so. The only time you need to replace the rims along with the tires are when you damage or lose them.
Tires have molded indicators called "wear bars." If these are visible across the tread pattern, your tires need to be replaced.
In my opinion the new tires go up front. The steering tires need the grip.
In the tread there are small 'bars' at the bottom surface about 2-3 mm high, when average tread wear is down to these 'bars' you should get new tires.