Tech: Information on Tire safety, inflation and speed ratings

We recently received a question about tire information, and what exactly all the numbers mean on the side of the tire.  Seeing how those 4 pieces of rubber are the only thing connecting you, the driver, to the road, we will provide a basic overview of tires and tire safety for passenger cars.  It will not be an end-all-say-all about tires, but it should provide you with enough information to help your decision making for a future set of tires.  Grab a cup of coffee if you need to stay awake as class is in session!  =) 

What makes a tire?  Simply put, a tire is constructed of mixture of rubber and silica compounds, with nylon or steel belts under the main tread to provide strength.  Tire construction varies with manufacturers, so each tire from a company will have a slightly different makeup compared to another.  The best tire to buy will depend on a number of factors:  your style of driving, weather conditions, price, etc. 

Passenger tires generally have sipes and grooves in them which aid in wet weather traction and channel water away from the tire to provide maximum contact with the road surface.  Brand new tires usually have at least 8/32" of tread.  To be legal for street use, a tire must have a minimum tread depth of 2/32".  Looking at your tire from above, you may see little "bars" which are embedded between the grooves.  These wear bars are indicators that your tire is approaching the limits of tire wear.  Once these bars are even with your tread, your tire is worn out.  To see if your tire is ok, take a penny and stick it in the groove of your tire with Lincoln's head facing down.  If most of his head is covered by the penny, your tire has at least 2/32" of tread left.