What Does The First Number In A Tire Size Mean

Tire Size Explained: What the Numbers Mean

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

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

If y'all're interested in switching out your tires for a unlike look or performance, a good place to starting time 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

Here'south what those numbers and indicators on the sidewall indicate and how to understand them:

A: TIRE Blazon The start letter in the code tells y'all what course of tire it is.

P stands for passenger vehicle tire. P-form 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 choice. These are frequently equipped on three-quarter or 1 ton trucks and SUVs.

ST stands for Special Trailer. These tire sizes are meant for trailers, including fifth wheels and other travel trailers, as well as boat and utility trailers.

If there's no letter before the offset number, you accept a metric tire most commonly referred to as European size. It'southward also measured in millimeters simply may take a different load capacity than a P or LT tire.

B: TIRE WIDTH The three-digit number following the alphabetic character is the tire'due south width (from side to side, looking at the tire head on) in millimeters. This may also be referred to as the section width.

C: Aspect RATIO The forwards slash separates the tire width number from the two-digit attribute 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 percent. It'south the superlative of the sidewall measured from wheel rim to top of the tread, expressed as a percentage of tire width.

In this instance, the attribute ratio is 65, meaning the sidewall is 65 per centum as high as the tire is broad. To get the sidewall acme, accept the tire width of 215 mm and convert it to inches (8.46). So multiply this past 65% (.65). This gives you an answer of five.5, the sidewall summit in inches.

D: Construction Blazon This single letter tells y'all virtually the internal construction of the tire.

R is for radial tires, the manufacture standard for most tires today. They accept amend road grip, lower rolling resistance for better gas mileage, ride comfort and durability than previous generations of tires. In a radial tire, the plies — layers of stiff 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, called bias-constructed tires. They are also chosen conventional, x-ply, or cantankerous-ply tires. Some motorcycle and trailer tires still apply this internal construction.

Bias construction tire diagram

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

Eastward: WHEEL Diameter This ii-digit number specifies cycle diameter in inches. It's the distance betwixt the 2 bead seat areas (where a tire gets tightly sealed onto the wheel).

How to measure wheel diameter

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

G: SPEED RATING The last letter is the tire speed rating. This indicates the meridian speed it's prophylactic to travel at for a sustained amount of time. A tire with a college speed rating tin can handle oestrus better and provide more control 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 course, you should ever abide by speed limits for safer driving.) Speed rating is usually, but not always, a single letter of the alphabet (see the chart).

Tire Size Charts

Beneath you volition find several charts that volition help you sympathise tire sizing numbers, including a load index nautical chart and speed rating chart.

Buying New Wheels or Irresolute Your Tire Size?

A tire size calculator is a quick mode to see whether the tire size yous're considering volition probable fit your car, SUV, sports car, low-cal truck or crossover.

But remember that is simply an estimate. It's important to stay inside the sizing tolerances of your vehicle. Tires that are the wrong size could cause some pull in the steering bicycle, rub against the suspension or torso of your vehicle, reduce clearance on hills, or result in a stiffer or noisier ride.

If you're considering mounting a different tire size on your vehicle, bank check with a tire good. Find out whether the tires and wheels you have your eye on are the correct fit for your vehicle'south suspension, gearing, and bodywork. And ask how any differences in revolutions per mile, tire speed, load index, and speed rating will affect your ride quality and vehicle functioning.

Run across how new tires and rims will expect on your automobile or truck using our Virtual Wheels simulator, available at whatever Les Schwab.

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