Tire Information/Terminology

The tire information provided will give you a better understanding of all aspects of your tire.


  • Aspect Ratio
  • Heat Cycle
  • How a Tire is Made
  • Load Index
  • Plus One Concept
  • Speed Rating


Tire Aspect Ratio -The ratio of section height to section width. A 70 series tire’s height is equal to 70% of its width. Lower profile tires have a lower aspect ratio. In general, tires with a lower section height (i.e. where the aspect ratio is lowered) have a higher cornering force and therefore improved performance and handling characteristics.

Load Index – Many tires come with a service description added on to the end of the tire’s size. These service descriptions contain a two-digit number which includes the load index and speed rating letter. The load index is a representation of the maximum load each tire is designed to support.

Plus One Concept – The plus one concept is the proper sizing up of a wheel and tire combination. Each time you add 1 inch to the wheel diameter, add 20mm to the tire width and subtract 10% from the aspect ratio. This compensates for the increases in rim width that generally accompanies the increases in diameter too. By using a larger diameter wheel with a lower profile tire, it is possible to properly maintain the overall rolling radius, keeping the odometer and speedometer changes negligible. However, be prepared for a stiffer ride as there will be less sidewall to cushion undulations in the road.

Speed Rating – All tires are rated with a letter representing speed capabilities. This indicates the maximum speed that the tire can sustain for a ten minutes without coming to pieces and destroying itself.

Use the following chart to determine the maximum load-carrying capacity based on a tire’s load index:

Letter MPH KM/H
P 95 150
Q100 160
R 106 170
S 112 180
T 118 190
U 124 200
H 130 210
V 150 240
W 168 270
Y 188 300
Z 149+ 240+