Section
Width:

The section width measures the width of the tire in millimeters.

For example, a tire with a section width of 225 is 225mm wide (approximately 8.85").

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Aspect
Ratio:

The Aspect Ratio of a tire describes the relationship between width of the tread and the height of the sidewall.

If a tire has an aspect ratio of 50, then it's sidewall is 50% as tall as the tread is wide.

For example, if a tire has a section width of 225 millimeters and an aspect ratio of 60, then it's sidewall height is:

225mm * 60% = 135mm

Or...

135mm / 25.4 = 5.3"

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Rim
Diameter:
Measures the diameter of the wheel on which the tire must be mounted.
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Service
Description:

Passenger tires are given a "Service Description" to describe the tire's capabilities.

A service description has two components:

• Load Index
  The load index corresponds to the load-carrying capacity of a tire.
  
  
• Speed Rating
  Speed ratings are intended to correspond to the maximum speed capability of a tire.
  
  Speed ratings are more useful in describing a tire's overall performance capability.

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