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Tires 101


Everyone has purchased tires for their vehicles at one time or another. Do you know how to buy the correct tire for your vehicle? Most of us count on the person selling us the tires to install the correct ones. Unfortunately this is not always the case. Every manufacturer will place a tire decal on the driver’s door frame to let you know the recommended tire size and in most cases the weight and speed rating. This information is also imbedded on the side wall of the tire. When purchasing tires these specifications should be taken into account for the replacement tires.

Let’s break down this example tire P245/40R18 93W. The “P” indicates it is a passenger car tire. You may also find LT to signify light truck or T for a temporary spare. The next number, in this case “245”, is the measurement across the width of the tread surface in millimeters. Basically this is how wide the tire is. This is important because it is dangerous to put a tire that is too wide or even too thin on your rim size. The next number “40” is the aspect ratio of the sidewall height compared to the width of the tire. In this case the side wall height is 40% of the tread width or 98mm. The lower the number, the thinner the side wall will be. Thinner side walls will make the car not absorb road imperfections as well because the material will need to be stiffer to support the vehicle’s weight. The letter “R” will be found on almost every tire because it stands for radial construction. Some of you may remember the days of bias ply tires which used to have a “D” code. There also used to be “ZR” that indicated a high speed radial but this is seldom used any more. Our next number “18” is the diameter of the rim the tire will fit. This will mostly be a whole number but there are some specialty rims that are an extra ½ inch as in 19.5”. The final set of digits “93W” will signify the weight and speed rating of the tire. This example has a weight rating of 1433lbs and the speed is 168mph. So the 4 tires on the vehicle will support a vehicle weight of roughly 5700lbs.

There is also other information stamped into the side wall of the tire. One is the max pressure the tire can hold safely. However the tire pressure you should keep in the tire is also found on the placard in the door jamb of your specific vehicle. Another number on the tire is the DOT code. This is the code supplied to the Department of Transportation to indicate the tires specifications. It also includes the tire manufactured date as the last 4 digits. If the last 4 digits are “2815”, this means the tire was made in the 28th week of the year 2015. You want to avoid buying tires that are over 2 years old. The reason being is the rubber will dry rot in about 5-6 years and you may not get the full tread life out of them before they become cracked and unsafe. Now to make things even more confusing replacement tires will have a tread wear, traction, and weather rating. These factors will also need to be considered when making your decision.

H&I Automotive carries multiple brands of tires to suit any need and budget. All tires come with lifetime balancing and nationwide road hazard protection is available. We have the latest high speed road force balance and precision wheel alignment equipment to ensure a proper ride from your new tires. Please call us for a free quote 480/985-9279. We are a full service professional automotive service center that has been serving our east valley neighbors since 2009. Find us online at www.handiautomotive.com or on facebook and google+.

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