Need-to-Know Facts About Tires

Photo courtesy Istockphoto/Bibigon
Photo courtesy Istockphoto/Bibigon

Tires are black and round —?that much about them never seems to change, except for various width of white sidewalls every couple of decades. Still, for most drivers, tires are an afterthought?—?often poorly maintained and taken for granted. Yet, ironically, those small patches of rubber are our only connection to the road.

Think you know everything about tires?

Goodyear tire says the P195/75R14 all-season passenger tire (their most popular size), weighs about 21 pounds and is made up of a combination of:

  • 4 lbs of 8 types of natural rubber
  • 5 lbs of 8 types of black carbon
  • 1 lb of steel cord for belts
  • 1 lb of polyester and nylon
  • 1 lb of steel bead wire
  • 3 lbs of 40 different kinds of chemicals, waxes, oils, pigments, etc.
  • 6 lbs of 5 different types of synthetic rubber

How do you “read” a tire?

Size Designation P185/75R14?—?means what exactly?
P? Identifies a tire: R = passenger car; T = temporary use (spare only); LT = light truck; ST = trailer tire
185 Cross-section width (in millimeters)
75 Aspect Ratio: The ratio of the tire height to the tire width, expressed as a percentage
R Construction type: R = Radial; B = Bias Belted; D = Diagonal
14 Rim Diameter (in inches) that the tire must be mounted on

What is This?


Tires carry a Transport Canada approval code that identifies the tire manufacturer and plant, tire make and model, and the date of production?—?and that’s the one you should care about.

In this example, the tire was built during the 45th week of the 8th year (probably 2008).

The DOT code is particularly useful when evaluating the fitness of trailer tires. Often this rubber appears to be in good shape because of little use, but rubber does age and become brittle. The older a tire is the more likely it is to have cracks in between the treads and on the sidewalls. But, you can’t count on these telltale signs?—?sometimes they don’t exist. Consider replacing trailer tires that are older than six years.

A few other tidbits…

New “low-rolling-resistance” tires can save fuel. Transport Canada says they can improve fuel consumption by 2.5 to 3.0 per cent.

Sidewall height affects ride quality and also weight carrying capability. Sidewall thickness (or number of ply) also affects these characteristics and together can be custom spec’d to suit your particular need.

Many tire companies today will register your tires?—?which means they will notify you directly if there is ever a re-call issue.

Refer to your vehicle’s owner’s manual for the proper level of inflation; it may also be posted on the door post or in the glove box.

Forget the eyeball test?—?it’s almost impossible to tell if a tire is low just by looking at it. Some radials can be as much as 50 per cent underinflated before they start to look soft. You need to check tires with a gauge. Check regularly, when the tires are cold.