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How to Read a Sidewall


The sidewall of your tires contains a great deal of information, including the manufacturer, its brand name and the type of construction. But what do the rest of the numbers and symbols mean? To find out, just click any of the codes shown our sample tire:

Vehicle RatingAspect RatioConstruction TypeDiameterLoad IndexSpeed RatingConditionsDot CodeMaximum PressureMaximum LoadQuality Ratings

Vehicle Rating

Vehicle Rating

The vehicle (or application) rating indicates the type of vehicle for which the tire is designed. In our example, the "P" indicates that this tire is designed for passenger vehicles. Other codes include: "LT" (Light Truck), or "T" (Temporary), which indicates that a tire is designed as a spare, to be used for short distances only.

If your existing tires have no vehicle or application code, the experts at Coast Tire & Auto Service can find the information you need to determine which tire is right for you.

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Aspect Ratio

Aspect Ratio

The first number in this group indicates the width of the tire, measured from sidewall to sidewall, in millimetres. The second number gives the sidewall height as a percentage of the width. In our example the tire is 215 mm wide, with a height that is 65 per cent of the width. Based on the calculation 215 x 0.65, the tire in our example has a sidewall height of 139 mm.

It is important to make sure your vehicle's tires are all the same size.

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Construction Type

Construction TypeThe "R" in the example above indicates a radial tire. Other codes you might find include: "B" for belted bias "D" for diagonal bias

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DiameterDiameter

This code shows the diameter of the tire, in inches. Our sample tire in this illustration is 15 inches across.

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Load Index

Load IndexThe load index describes how much weight the tire can carry at maximum inflation pressure. The number shown here is a code, not the actual weight measurement. The code of 89 indicates that this sample tire can support a maximum of 580 kilograms.

The load index codes range from 0 to 279 with the majority of passenger tires rated between 70 and 110. You can view a list of the load index codes and their corresponding weight values by clicking here.

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Speed Rating

Speed RatingThe speed rating is a letter code, from A to Z, that indicates the maximum speed capabilities of the tire. This speed rating is only valid for tires that are properly inflated and carrying loads within their assigned load index.

To view a list of the most common ratings and their associated speeds in km/hour, click here.

To protect your ability to control your vehicle, you should only install tires with a speed rating that is equal to or higher than your vehicle manufacturer's recommendation.

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Conditions

ConditionsSnow TireIn our example, "M+S", (Mud and Snow), indicates an all-season tire. The snowflake and mountain symbol on the side of a tire indicates that it meets or exceeds the new snow tire designation specifications, and will provide you with optimum traction in severe snow conditions.

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DOT Number

DOT NumberAll tires sold in Canada must have the "DOT" ((Department of Transportation), or tire identification number, moulded into the sidewall. Our tire has a DOT number of GHYT 4501. The first two characters after DOT indicate the manufacturer; the second two characters indicate the plant where the tire was manufactured.

Next you may see an optional string of three to four characters. Our example does not include this code. Most manufacturers use these to record company specific information about the tire, and, if necessary, use them as a guide when issuing product recalls. Because they are company specific, these codes are not standardized and are meaningful only to the manufacturer.

The last three or four digits give the date the tire was made. For all tires built after 1999, this will be a four-digit number with the first two digits giving the week number, and the last two giving the year. For many tires built previous to 2000, the date indicator will consist of three digits, the first two giving the week number and the last giving the last digit of the year. In our example tire, the last four digits of the DOT code are 4501, so our tire was made during the 45th week of 2001.

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Maximum Pressure

Maximum PressureThis number gives the maximum cold pressure required to carry the maximum load for which the tire is rated. The maximum pressure number is not the same as the recommended tire pressure for your vehicle.

Important:  Never exceed the maximum pressure written on your tire's sidewall. Explosive failure may occur as a result, leading to serious injury or death.

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Maximum Load

Maximum LoadThis number tells you the maximum amount of weight the tire can support when cold. Remember, cold means the tire has been driven less than 2 km, or has been standing still for at least three hours.

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Quality Rating

The quality rating consists of three measurements, all of which are tested under controlled conditions and graded to a standardized system. These measurements are treadwear, traction and temperature.

Please note that these ratings are based on a relative scale, and each manufacturer assigns the scale across its own product lines. This means that although the grading system is good for comparing tires of the same manufacturer, it may not be accurate for comparing tires produced by different manufacturers.

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Treadwear: 

Treadwear

This rating measures how long the tread takes to wear down. The higher this number, the longer the tread should last. For example, a tire with a treadwear rating of 400 should last twice as long as one with a treadwear rating of 200.

The actual rate of treadwear for your tires depends on your unique road conditions, climate and tire maintenance.

Traction: 

Traction

This rating describes the tire's ability to stop on wet pavement and concrete. Traction rating tests are conducted on vehicles driving straight ahead, and do not measure the tire's cornering abilities.

Traction ratings are written (from highest to lowest) as "AA", "A","B", and "C".

Temperature: 

Temperature

Driving creates heat. Excessive heat for prolonged periods can degenerate the materials in your tires, and, under extreme conditions, can lead to explosive failure. A tire's temperature grading measures the tire's ability to withstand and dissipate heat under controlled, indoor laboratory testing.

A tire's temperature resistance is assigned the following grades (from highest to lowest):   "A", "B",and "C".

 

For More Information

As you can see, there are many factors to consider when choosing new tires. Save money. Stay safe on the road. Visit your local Coast Tire & Auto Service and let us help you make this important choice today.

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