Tire Sizing Guide

Tire Sizing Guide

The tire size branded on the sidewall supplies a substantial amount of info about the tire's intended purpose, dimensions, load capability and high temperature/high-speed resilience.

Our primary example will be based upon variations of the 225/50R16 size, although other sizes will appear where proper.

"The tire size branded on the sidewall offers a considerable quantity of information about the tire's desired function, measurements, load ability and high temperature/high-speed sturdiness.".


Before we get started check out this video so you understand where to look on your tire and what the numbers mean.

Service Type

Many tire sizes begin with a letter or letters that recognize the type of automobile and what kind of service for which they were designed. The typical indications are as follows:.

P225/50R16 91S.

P = When a tire size starts with a "P," it represents the tire is a "P-metric" size that was developed to be fitted on vehicles that are primarily made use of as passenger cars. This includes automobiles, minivans, sport utility vehicles and light responsibility pickup (typically 1/4- and 1/2-ton load ability). Making use of P-metric sizes started in the late 1970s and they are the most regularly utilized type of tire size today.

225/50R16 92S.

If there isn't a letter preceding the three-digit numerical portion of a tire size, it symbolizes the tire is a "Metric" size (also called "Euro-metric" since these sizes come from in Europe). While Metric tire sizes are primarily used on European vehicles, they are also utilized on vans and sport energy cars. Euro-metric sizes are dimensionally comparable to P-metric sizes, however generally vary subtly in load bring abilities.

T125/90D16 98M.

T = If a tire size starts with a "T," it symbolizes the tire is a "Momentary Spare" ("space saver" or "tiny spare") that was designed to be utilized temporarily only up until a flat tire can be repaired or changed.

LT245/75R16 108/104S.

LT = If a tire size starts with "LT," it signifies the tire is a "Light Truck-metric" size that was designed to be used on automobiles that are capable of hauling heavy cargo or towing large trailers. This includes medium and durable (typically 3/4- and 1-ton load capability) pickup, sport utility vehicles, and full-size vans. Tires branded with the "LT" classification are the "little brothers" of 18-wheel tractor-trailer tires and are designed to supply substantial reserve capability to accept the additional tensions of hauling heavy freight.

7.50 R16LT 112/107Q, 8.75 R16.5 LT 104/100Q or 31x10.50 R15LT 109Q.

LT = If a tire ends with "LT," it symbolizes the tire is either an earlier "Numeric", "Wide Base" or "Flotation" Light Truck size created to be utilized on cars that are capable of bring heavy freight and towing trailers (Numeric sizes), usage 16.5-inch diameter rims (Wide Base sizes) or are larger, over sized tires designed to assist the car drive on top of loose dirt or sandy surfaces (Flotation sizes). This includes light, medium and heavy task (generally 1/2-, 3/4 and 1-ton load ability) pickup and sport utility cars. Tires branded with the "LT" at the end of their size classification are likewise the "little bros" of 18-wheel tractor-trailer tires and are developed to offer substantial reserve capacity to accept the additional anxieties of hauling heavy cargo.

195/70R15C 104/102R.

C = If a Euro-metric sized tire ends with a "C," it signifies the tire is an "Industrial" tire meant to be used on vans or delivery van that are capable of carrying heavy loads. In addition to being branded with the "C" in their size, these tires are likewise branded with their proper Service Description.


ST = If a tire size starts with "ST," it symbolizes the tire is a "Special Trailer Service" size that was created only to be utilized on boat, automobile or energy bill trailers. ST-sized tires ought to never be utilized on cars, vans or light trucks.

Section Width

Following the letter(s) that recognize the type of car and what type of service for which the tire was created, the three-digit numeric part identifies the tire's "Section Width" (random sample) in millimeters.

P225/50R16 91S.

The 225 suggests this tire is 225 millimeters across from the widest point of its external sidewall to the widest point of its inner sidewall when installed and determined on a defined width wheel. This measurement is also described as the tire's area width. Since lots of people consider measurements in inches, the 225mm can be converted to inches by dividing the area width in millimeters by 25.4 (the number of millimeters per inch).

225mm/ 25.4 = 8.86".

Sidewall Aspect Ratio.
Following the three digits identifying the tire's Section Width in millimeters is a two-digit number that determines the tire's profile or element ratio.

P225/50R16 91S.

The measurement is the tire's area height and likewise referred to as the tire's series, profile or aspect ratio. By converting the 225mm to inches (225/ 25.4 = 8.86") and increasing it by 50 % (.50) we verify that this tire size results in a tire area height of 4.43". If this tire were a P225/70R16 size, our estimation would verify that the size would result in an area height of 6.20", approximately a 1.8-inch taller sidewall.

Internal Building

A letter (R in this case) that determines the tire's internal construction follows the two digits used to determine the aspect ratio.

P225/50R16, P225/50ZR16.

The R in the P225/50R16 91S size determines that the tire has a Radial construction in which the tire's body plies "radiate" of the imaginary center of the wheel. Radial tires are by far the most popular kind of tire today representing over 98 % of all tires sold.

If the R in the size were changed with a D (225/50D16), it would determine that the internal tire body plies crisscross on a Diagonal which the tire has a "prejudice ply" construction. Tires utilizing this building are for light truck and extra tire applications.

If the R in the size were changed with a B (225/50B16), it would identify that the tire body plies not just crisscross the tire on a diagonal as previously, but that they are strengthened with belts under the tread location. This type of tire construction is called "Belted." Tires utilizing this building are practically extinct.

The European Tire and Rim Technical Organisation (ETRTO) has adopted branding standards that allowed tire producers to identify tires with self-supporting run-flat buildings within the tire size classification. Self-supporting run-flat tires might be recognized with the letter F instantly following the conventional letter recognizing tire building (such as the R designating radial) within the size.

This results in size classifications such as 225/45RF17 91Y (for self-supporting run-flat tires that have a speed record recognized in their Service Description and 255/40ZRF20 (for Z-speed ranked self-supporting run-flat tires in which the speed rating is contained in the tire size).

Since this tire size classification was adopted well after the introduction of self-supporting run-flat tires into the marketplace, self-supporting run-flat tires introduced and produced before it went into impact will not be required to be branded.

Speed Rating

Today, the only tires that continue to consist of the speed score "in" the tire size (P225/50ZR16) are Z-speed ranked tires. In this case, following the two digits utilized to determine the aspect ratio are the letters ZR to determine the tire's speed score (Z) and its internal building (R). Because 1991, all other speed ratings are determined in the tire's Service Description (which will be covered shortly).

Tire and Wheel Diameter

P225/50R16 91S.

The 16 suggests the tire and wheel size developed to be matched together.

Tires that have a rim diameter expressed in inches (P225/50R16, as well as 8, 10, 12, 13, 14, 15, 17, 18, 19, 20, 22, 23, 24, 26 and 28) are called "inch rim" sizes. These are the most typical types of tire sizes and are used on the majority of automobiles, minivans, vans, sport utility vehicles and light task light trucks.

While not as typical, two extra "distinct" types of tire/wheel sizes are still in usage today.

Tires and wheels that have a rim diameter revealed in "half" inches (8.00 R16.5 LT, in addition to, 14.5, 15.5, 17.5 and 19.5) are made use of on some sturdy trailers, heavy-duty trucks, and box vans.

Tires and wheels that have a rim diameter expressed in millimeters (190/65R390, as well as, 365 and 415) are called millimetric sizes. Michelin initiated millimetric sizes for their TRX tires that saw minimal use on lots of various automobile designs in the late 1970s and 1980s.

Michelin PAX System run-flat tires have been introduced as an integrated wheel/tire system on an extremely restricted basis as Initial Equipment (O.E.) in North America. An example PAX System size of 235/710R460A 104T expresses tire and wheel dimensions in millimeters (235 mm Area Width, tire Total Size of 710 mm and a 460A mm rim diameter, with the "A" in 460A symbolizing these tires include "asymmetric" beads in which the outdoors bead (450 mm) and inside bead (470 mm) are in fact different sizes.

All of these "distinct" tire/wheel sizes were established particularly because the tire and wheel design or planned automobile usage required them to be different than conventional tires and wheels. All these tires and wheels include bead profiles that have a various shape than conventional "inch rim" sizes.

Tires and wheels with special rim sizes must never be integrated with conventional "inch rim" tires and wheels.

It is important that the tire and wheel diameters are always validated to match before the tire is installed on the wheel.