When it comes to buying tires for your Ford, it may take learning a new language.  Tires are sized and marked with a special code that will probably require your Ford Dealer Service Department to decipher.

The codes you will find on tires can be very confusing, but they are also very important.  Installing the wrong size tires, unlike choosing new floor mats or seat covers, can have adverse effects.  A sample tire code might be:  P225/50R1691S. Here’s a breakdown of that sample code:

•    The “P” means the tire is meant for passenger vehicles like mini vans cars, small trucks, and SUVs.
•    The “225″ is the measurement of the widest point of the tire’s outer sidewall to the widest point of its inner sidewall when installed.
•    The “50″ is the percent of the sidewall height relative to the width. (In this example, since the width is 225 millimeters, the sidewall height from the rim to the tread is 112.5mm)
•    The “R” denotes how the internal construction of the tire was fabricated. In this example, “R” means radial.
•    The “16″ is the size of the rim.
•    The “91S” is the service description of the tires. The “91″ is the number that rates how much load the tires can handle. (The “91″ in this example means that the tire can handle 1356 pounds.) The bigger the number, the greater the tire’s capacity.
•    The “S” is the tire’s speed rating. (An “S” speed rating denotes that the tire can operate safely at speeds up to 112 miles per hour. The further down the alphabet, the higher the velocities that are safe for the tire.)

So what does this all mean? Typically, a car that’s made for speed will have a wider width with a low alphabet letter (generally W, Y, or Z) and a low percentage of sidewall for optimal handling and steering capabilities. A passenger vehicle, meanwhile, will have a medium width and a higher percentage of sidewall for a more luxurious style.

Tinkering with tires without knowledge about tire sizes can be dangerous for several reasons:
•    Odometers and speedometers are calibrated based on the height of a vehicle’s tires. Taller tires make speedometers read slower than the actual speed of the vehicle.
•    More recent vehicles have built-in computers that base calculations on the height of a vehicle’s tires. Changing tires could result to a vehicle’s components malfunctioning.
•    Stock suspension systems could suffer additional stress with taller tires, resulting in accelerated wear, tear, and/or failure. If one makes substantial changes in tire height, one should upgrade and bolster the vehicle’s stock suspension.
So when in doubt, always check with your Ford Dealer Service Department.  Whether you’re driving a Ford Focus or a F-250, your dealer wants you to be safe and properly equipped.