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The Tire and rim are essential elements of any vehicle. They assist in the vehicle’s road-handling ability, steering stability, and braking capability. While a vehicle’s rim(s) does not need regular replacement, tires, regardless of the type, will eventually need to be replaced.

Purchasing a new tire or tires can be a stress on anyone’s budget; however, purchasing a used tire(s) can be a viable alternative. Buying a used tire is somewhat different than buying a new tire because a used tire is typically purchased from someone other than a tire dealer. That is why the used tire purchaser must be armed with some extra knowledge about tires and rims.

If you are quite familiar with the tire you need for your vehicle, you might be a little more confident in doing this. However, with newbies, this can easily go wrong—so research is a must. Start with knowing the best type and brand of tire for your car. If you have a Prius, check out every article on the best tires for Prius (RatedRadarDetector has a pretty good list for Prius). Familiarize yourself with the names and brands, then learn a few more details about the tires. Our simple guide below should help you out.

The Tire and Rim Should Always Match

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The tire’s visual appearance is most noticeable, but it should never be the only factor used in making a used tire purchase decision. The primary issue of concern should always be the size of the tire and size of the rim that will be used with the tire.

A common mistake that can cause a vehicle to become unsafe to drive is mounting the incorrect size tire to a rim. Indeed, because tires are flexible, an incorrectly sized tire can be mounted to a rim of the wrong size. Many people believe that if the tire fits the rim, then that tire and rim are a good match. Rims are manufactured to accept a specific tire with specific size requirements, and mismatching them can cause the vehicle to become unstable while turning a corner or coming to a hard stop.

What Tire Size Numbers Mean

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Tires size values are typically molded into the sidewall of the tire. To determine the size of tires, a special table on the website can help you, which contains information on different cars brands and models and is regularly updated. There are other numbers molded into the sidewall as well, but the numbers that show the tire size are significantly larger than the other numbers appearing along the sidewall. Let us use 285/80 R14 for an example. The first number is a measurement in millimeters that indicates the width of the tire (285mm).

This first number is three (3) digits long and is followed by a forward slash and a 2-digit number. This second number is an indication of the tire’s height that is also expressed in millimeters. This 2-digit number is actually a percentage of the tire’s width. The standard is 80%, so if the sidewall is missing this second set of numbers it is because the height of the tire is 80% of the width. In this example, the height of the tire is 80% of the width, or 228mm (285 times 80%).

The last number in the group is preceded by a capital letter “R”. The letter “R” is an indication that the tire is a radial. The number is the diameter of the tire, and it is expressed in inches. The example tire size shows that the tire has a diameter of 14 inches.

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Some tires may also have a letter designation that appears before the first set of tire size numbers. The letter “P” indicates the tire was designed for a passenger vehicle, the letters “LT” means the tire was designed for a light truck, and the letter “T” means that the tire should only be used as a “temporary” or spare tire.

The other numbers molded into the tire sidewall will provide the tire’s maximum load, heat-dissipating capabilities, proper inflation pressure, and its speed rating. Additionally, there will be informed as to how the tire was constructed. The construction indicates the number of plies, belts, and if the tire is a bias-ply or steel-belted radial.

Mixing bias-ply tires and radials should never be done because the tires have completely different handling capabilities. Mixing the two types of tires on the same vehicle could cause driving stability and handling problems.

Rim Measurements

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Vehicle manufacturers have taken great pains to generate rims that are a match to the vehicle. Rims are manufactured in specific diameters and have limited weight handing abilities. Normally, the rim’s size and weight class is stenciled onto the outside edge of the rim. The rim’s size is expressed in inches. The diameter measurement of the rim is taken from the interior side where the tire will sit.

The rim’s weight class is a rating that indicates the amount of weight the rim can handle under normal driving conditions. For safety reasons, the weight rating of the rim should always be higher than the vehicle’s curb weight. Additionally, all four of the rims should be the same size, and have the same weight rating.

Rims will normally accept a narrow range of tire sizes. This becomes a critical factor when considering the width of the tire and rim. Tires that are too narrow will wobble within the rim and cause the vehicle to drift from side-to-side, and stability when cornering will be lost as well.

Mounting a tire to a rim that is wider than the rim’s acceptable limit can cause excessive stress on the tire’s sidewall when the vehicle is driven, which could result in a tire blowout. The vehicle will also exhibit erratic handling because the weight of the vehicle is not being centered onto the center of the rims.

Buying used tires is a good way to save money, but it is wise to do a little investigation before making the purchase. The tire’s physical inspection, both inside and outside the tire, will indicate damage and tire weakness. However, a tire that is good physically may not be the best match for your vehicle. Tire and rim size should always be the number-one concern when looking to buy used tires for your vehicle.