Proper tire inflation is essential for safe driving and long tire life. It’s a good idea to check your tires’ air pressure at least once a month with an accurate tire pressure gauge. Be sure to check pressure while your tires are cold and have not been used recently. Even driving a mile will cause your tire pressure to increase and give you an inaccurate reading.
If your car pulls to one side and you haven't recently wrecked your car, you most likely just need to replace your tires. A busted belt will cause a vehicle to pull to one side. If you suspect this is the case, you can simply swap the two front tire or to rear tires to the opposite side and see if it doesn't pull in the opposite direction. If it does, then simply have the tires replaced and NO NEED FOR AN ALIGNMENT.
If you think you have a leak in a tire, check out the valve stem on the tire before you take it to a mechanic.
To determine whether the core of the valve stem is leaking, remove the cap and use your finger to apply a little soapy water around the valve. If bubbles form, the core is leaking and needs to be replaced. You can get a new core and a valve-repair tool at any auto-parts store.
Here's how to replace the valve core:
Carefully jack up the car so you can let the air out of the tire.
Unscrew the valve using the repair tool.
Safety tip: Be careful! The valve can fly out just from the pressure in the tire.
Screw the new valve core in place and refill the tire with the proper amount of air. Then retest to make sure the new valve core is functioning properly. If it is, put the valve cap back in place.