How to Read Tire Size

How to Read Tire Size: Understanding 205/55R16 and Other Codes

Tire size looks confusing at first, but it follows a very logical pattern. Once you understand what the numbers and letters mean, you can quickly check if a tire fits your vehicle and driving needs. This guide uses 205/55R16 as the main example and shows how to decode any other tire size you see on the sidewall.

Where to Find Your Tire Size

Reading the sidewall

The easiest way to find your tire size is to look at the sidewall of one of your current tires. You’ll see a code printed in large characters, such as 205/55R16 91H or 225/65R17 102T .

The first part (for example 205/55R16) is the size.
The numbers and letter that follow (for example 91H) describe load index and speed rating.

All four tires on a passenger car are usually the same size. If they are different, always verify which size the vehicle manufacturer recommends before buying replacements.

Other places to check the recommended size

Relying only on what is currently mounted can be risky if a previous owner installed the wrong size. To be sure, also check:

Tire and Loading Information label
- Located on the driver’s door jamb or the pillar behind the door.
- Lists original front and rear tire sizes and the recommended cold inflation pressures.
Owner’s manual
- Confirms factory‑approved sizes and sometimes lists alternate sizes for optional wheels, towing packages, or performance trims.

Whenever possible, match the tire size, load index, and speed rating shown on these factory references. This keeps handling, braking, and safety systems performing as designed.

What Does 205/55R16 Mean?

Let’s break down 205/55R16 into simple parts. Each number and letter describes a specific dimension of the tire.

205 – Tire width (section width)

The first number is the section width , measured in millimeters from sidewall to sidewall.

A 205 tire is approximately 205 mm wide.
A wider number (for example 225 or 245) means a wider footprint on the road, which can improve cornering grip but may increase rolling resistance and fuel consumption.

55 – Aspect ratio (sidewall height)

The second number is the aspect ratio , the sidewall height expressed as a percentage of the tire width.

In 205/55R16, the sidewall height is 55% of 205 mm, or about 113 mm.
A lower aspect ratio (45, 40, etc.) gives a shorter, stiffer sidewall for sportier handling but a firmer ride.
A higher aspect ratio (60, 65, 70) adds more sidewall, which usually improves comfort but can make steering feel less sharp.

R – Construction type

The letter that follows is the construction type .

R stands for radial, the modern standard for almost all passenger vehicles.
Radial tires have layers of cord running radially across the tire, which improves durability, comfort, and fuel economy.

Other letters (such as B or D) are rare on modern passenger cars and usually indicate older bias‑ply or belted constructions used in specialty applications.

16 – Wheel diameter

The last number in the size portion of the code is the rim (wheel) diameter , measured in inches.

205/55R16 fits a 16‑inch wheel.
This number must match the wheel exactly; you cannot mount a 16‑inch tire on a 17‑inch wheel or vice versa.

91H – Load index and speed rating (optional but important)

Most tires also include numbers and a letter after the size, such as 91H in 205/55R16 91H .

91 – Load index

The load index is a code that corresponds to the maximum weight the tire can safely carry when properly inflated.

For example, 91 usually means a maximum load of 615 kg (1356 lbs) per tire.
Load index tables are standardized, so every brand uses the same values for each number.

Always choose a tire with a load index that meets or exceeds the value specified on the door label. Going lower can overload the tire, leading to excessive heat buildup and possible failure.

H – Speed rating

The final letter is the speed rating , which shows the maximum sustained speed a tire is designed to handle under load.

Common speed ratings for passenger cars include:

T – up to 118 mph (190 km/h)
H – up to 130 mph (210 km/h)
V – up to 149 mph (240 km/h)
W – up to 168 mph (270 km/h)

You should not install a tire with a lower speed rating than the one recommended by the vehicle manufacturer, especially on vehicles where speed capability and stability are safety critical.