2010 Ford F-150 Lariat Tire Size

This letter denotes the intended use of the tire.

This number indicates that your tire has a width of 275 millimeters.

This number means that your tire has an aspect ratio of 65%.  In other words, your tire's sidewall height (from the edge of the rim to the tire's tread) is 65% of the width.  In this case, the sidewall height works out to be 178.75 millimeters.

This letter denotes how your tire was constructed.  Radial is the standard construction method for about 99% of all tires sold today.

The tire size was designed to fit rims or wheels that are 18 inches in diameter.

The mark of C denotes your tire's load range, or ply rating.  A load range of C means that the tire has a ply rating of 6.  Letters further along in the alphabet represent stronger tires that can sustain higher inflation pressures.  Tires with higher inflation pressures can carrier heavier loads.

This tire has a load index of 113, which means it's capable of carrying a load of 2530 pounds (1150 kg) or less.  A higher number means the tire can carry more weight.  A lower number means the opposite.

This tire has a speed rating of S, which means 112 mph (180 km/h) is the maximum speed that can be sustained for 10 minutes.  A higher speed becomes dangerous.