What Does The R Stand For In Tire Size

Tire Size Explained: What the Numbers Hateful

Tire size can be confusing. Some numbers on the sidewall are listed in millimeters while others are inches. Plus, the correct size for your machine, truck, or trailer tin differ depending on where and how you drive.

You can see your original equipment tire size in your owner'due south transmission or on the placard generally located on the driver's side door jam. This is the sizing recommended by the vehicle manufacturer.

If y'all're interested in switching out your tires for a dissimilar await or performance, a good place to outset is the numbers and other indicators on your existing tires' sidewall. Next, have a tire professional help you determine a tire size range that will fit your vehicle and driving needs.

Tagged diagram of tire size meanings

Tire Size Meanings

Hither'southward what those numbers and indicators on the sidewall betoken and how to understand them:

A: TIRE Blazon The first letter in the code tells you lot what class of tire it is.

P stands for rider vehicle tire. P-course tires include cars, SUVs, crossovers, minivans and smaller pickup trucks.

LT means light truck tire, designed for vehicles that are capable of carrying heavy loads, towing trailers, or for those looking for an extra heavy duty option. These are often equipped on three-quarter or 1 ton trucks and SUVs.

ST stands for Special Trailer. These tire sizes are meant for trailers, including 5th wheels and other travel trailers, too equally boat and utility trailers.

If there'south no letter before the first number, you accept a metric tire most normally referred to as European size. Information technology's also measured in millimeters but may have a unlike load chapters than a P or LT tire.

B: TIRE WIDTH The 3-digit number post-obit the letter is the tire's width (from side to side, looking at the tire head on) in millimeters. This may as well be referred to as the section width.

C: ASPECT RATIO The forward slash separates the tire width number from the 2-digit aspect ratio. The bigger the aspect ratio, the higher/taller the tire's sidewall, or "profile" as it's sometimes chosen.

The aspect ratio is indicated on the tire sidewall as a percentage. It's the acme of the sidewall measured from wheel rim to elevation of the tread, expressed equally a percent of tire width.

In this instance, the aspect ratio is 65, meaning the sidewall is 65 percent every bit high as the tire is wide. To become the sidewall height, have the tire width of 215 mm and convert it to inches (8.46). Then multiply this by 65% (.65). This gives you an reply of five.5, the sidewall meridian in inches.

D: CONSTRUCTION Blazon This unmarried letter tells you about the internal construction of the tire.

R is for radial tires, the industry standard for most tires today. They accept amend road grip, lower rolling resistance for ameliorate gas mileage, ride comfort and durability than previous generations of tires. In a radial tire, the plies — layers of strong cords made of a alloy of polyester, steel and fabric and coated with rubber — are laid perpendicular to the direction of travel.

Radial construction tire diagram

D is for tires built with diagonal (crisscrossed) plies, chosen bias-constructed tires. They are also called conventional, 10-ply, or cross-ply tires. Some motorcycle and trailer tires still use this internal structure.

Bias construction tire diagram

Some run-flat tires are identified with an F followed by the type of internal structure.

E: WHEEL DIAMETER This two-digit number specifies wheel bore in inches. It'south the distance between the two bead seat areas (where a tire gets tightly sealed onto the wheel).

How to measure wheel diameter

F: LOAD Index The two-digit or three-digit number that follows the gap specifies tire load index. The load index symbol indicates how much weight a tire can support, based on the following standard chart. In our example, the load alphabetize is 89, which indicates the tire has a load capacity of i,279 pounds, when inflated to the tire's maximum air pressure rating.

G: SPEED RATING The last letter is the tire speed rating. This indicates the pinnacle speed information technology's safety to travel at for a sustained amount of time. A tire with a higher speed rating tin handle heat amend and provide more command at faster speeds. The maximum operating speed of a vehicle is no more than than the lowest speed rating of all tires mounted on the vehicle. (Of form, you should always abide by speed limits for safer driving.) Speed rating is commonly, but not always, a single letter (see the nautical chart).

Tire Size Charts

Below you will find several charts that will assistance y'all sympathise tire sizing numbers, including a load index chart and speed rating chart.

Ownership New Wheels or Irresolute Your Tire Size?

A tire size calculator is a quick way to see whether the tire size you lot're considering will likely fit your auto, SUV, sports auto, light truck or crossover.

But call up that is only an judge. It's of import to stay inside the sizing tolerances of your vehicle. Tires that are the wrong size could cause some pull in the steering wheel, rub confronting the suspension or torso of your vehicle, reduce clearance on hills, or outcome in a stiffer or noisier ride.

If yous're considering mounting a dissimilar tire size on your vehicle, check with a tire expert. Find out whether the tires and wheels you have your heart on are the correct fit for your vehicle's break, gearing, and bodywork. And ask how whatever differences in revolutions per mile, tire speed, load index, and speed rating will touch on your ride quality and vehicle performance.

Run across how new tires and rims will wait on your auto or truck using our Virtual Wheels simulator, available at whatsoever Les Schwab.

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