Question: "How much air goes in my tires?"
Answer: That depends on a few different factors.
The tire type
The car
The manufacture of either of the first two
Temperature
Your car will have a tag similar to this. You can find it inside the door frame when you open the door and look in the door jamb. The manufacturer recommended pressures for your vehicle will be listed here.
Notice how it lists front and rear pressures. This is because the manufacturer has weighed your vehicle front and rear and factored in towing and loaded capacities when recommending those pressures. These pressures are for safety, grip, comfort, and life of your tires. It is advised to keep them at the pressure stated.
All tires have a maximum pressure listed on the outside of the tire. This maximum pressure is for safety whether loaded or unloaded. It can be extremely dangerous to operate your vehicle with overinflated tires and drastically reduces your tire life. An overinflated tire is an explosion hazard, so take care when inflating your tires.
Conversely, under inflation can be dangerous as well as an improperly inflated tire will cause your vehicle to "wonder" as the sidewalls of the tires are no longer tight enough to hold them stable while driving. Not only is under inflation dangerous, but it's also bad for your car. Under-inflated tires make your engine work harder resulting in poor fuel economy and poor car performance and comfort. Underinflation also drastically reduces the life span of your tires.
Proper tire inflation is super important for the everyday operation of your vehicle. Let's look at some take-aways.
Proper tire inflation pressures can be found inside your door jamb
Overinflation is dangerous and decreases the life of your tires
Underinflation can be dangerous and decreases the life of your tires
Improper inflation affects the fuel economy and performance of your vehicle
If you're uncomfortable with checking/adding air to your tires, see a professional