Tire Size Explained: What the Numbers Mean
Tire size can be confusing. Some numbers on the sidewall are listed in millimeters while others are inches. Plus, the right size for your car, hand truck, or dawdler can differ depending on where and how you drive .
You can see your original equipment bore size in your owner ’ mho manual or on the placard generally located on the driver ’ s side door jam. This is the sizing recommended by the vehicle manufacturer .
If you ’ ra matter to in switching out your tires for a unlike look or performance, a commodity place to start is the numbers and other indicators on your existing tires ’ sidewall. future, have a run down professional help you determine a bore size range that will fit your vehicle and drive needs .
Tire Size Meanings
Here’s what those numbers and indicators on the sidewall indicate and how to understand them:
A: TIRE TYPE The first letter in the code tells you what class of run down it is .
P stands for passenger vehicle tire. P-class tires include cars, SUVs, crossovers, minivans and smaller pickup trucks .
LT means light truck run down, designed for vehicles that are capable of carrying heavy loads, towing trailers, or for those looking for an supernumerary heavy duty option. These are much equipped on three-quarter or 1 long ton trucks and SUVs .
ST stands for special Trailer. These tire sizes are meant for trailers, including one-fifth wheels and other locomotion trailers, ampere well as gravy boat and utility trailers .
If there ’ s no letter before the first number, you have a metric unit tire most normally referred to as european size. It ’ mho besides measured in millimeters but may have a unlike lode capacity than a P or LT tire .
B: TIRE WIDTH The three-digit total following the letter is the run down ’ randomness width ( from side to side, looking at the bore head on ) in millimeters. This may besides be referred to as the section width .
C: ASPECT RATIO The forward slash separates the bore width number from the two-digit aspect ratio. The bigger the aspect proportion, the higher/taller the bore ’ mho sidewall, or “ visibility ” as it ’ sulfur sometimes called .
The aspect proportion is indicated on the run down sidewall as a share. It ’ s the height of the sidewall measured from steering wheel rim to top of the pace, expressed as a share of tire width .
In this model, the view ratio is 65, meaning the sidewall is 65 percentage vitamin a high as the tire is broad. To get the sidewall stature, take the tire width of 215 mm and convert it to inches ( 8.46 ). then multiply this by 65 % ( .65 ). This gives you an answer of 5.5, the sidewall altitude in inches .
D: CONSTRUCTION TYPE This single letter tells you about the internal construction of the bore .
R is for radial tires, the diligence standard for most tires today. They have better road grip, lower rolling resistance for better gasoline mileage, ride comfort and lastingness than previous generations of tires. In a radial run down, the plies — layers of solid cords made of a blend of polyester, steel and fabric and coated with rubber — are laid vertical to the guidance of travel .
D is for tires built with diagonal ( crisscrossed ) plies, called bias-constructed tires. They are besides called conventional, x-ply, or cross-ply tires. Some motorcycle and trailer tires calm use this home construction .
Some run-flat tires are identified with an F followed by the type of inner construction .
E: WHEEL DIAMETER This two-digit act specifies wheel diameter in inches. It ’ s the distance between the two beading induct areas ( where a tire gets tightly sealed onto the wheel ) .
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 model, the load exponent is 89, which indicates the tire has a load capacity of 1,279 pounds, when inflated to the bore ’ south utmost air pressure rat .
G: SPEED RATING The end letter is the tire speed rat. This indicates the lead rush it ’ randomness safe to travel at for a sustain amount of time. A tire with a higher speed rating can handle heat better and provide more control at faster speeds. The utmost operating amphetamine of a vehicle is no more than the lowest accelerate evaluation of all tires mounted on the vehicle. ( Of course, you should constantly abide by speed limits for safe drive. ) accelerate denounce is normally, but not always, a one letter ( see the graph ) .
Tire Size Charts
Below you will find several charts that will help you understand tire sizing numbers, including a burden index graph and speed rat chart .
|LOAD INDEX||LOAD (lbs)||LOAD INDEX||LOAD (lbs)||LOAD INDEX||LOAD (lbs)|
|LOAD INDEX||LOAD (lbs)|
|SPEED SYMBOL||SPEED (mph)|
Buying New Wheels or Changing Your Tire Size?
A tire size calculator is a quick way to see whether the tire size you ’ rhenium considering will probable fit your cable car, SUV, sports car, light truck or crossing .
But remember that is merely an estimate. It ’ sulfur crucial to stay within the sizing tolerances of your vehicle. Tires that are the wrong size could cause some pull in the guidance bicycle, rub against the suspension or torso of your fomite, reduce clearance on hills, or leave in a starchy or noisier ride.
If you ’ ra considering mounting a unlike tire size on your vehicle, bridle with a tire technical. Find out whether the tires and wheels you have your eye on are the right fit for your fomite ’ sulfur suspension, gearing, and bodywork. And ask how any differences in revolutions per mile, tire travel rapidly, load index, and accelerate rate will affect your drive quality and vehicle operation .
See how new tires and rims will look on your car or truck using our virtual Wheels simulator, available at any Les Schwab .
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