Understanding tire measurements correctly is essential for any vehicle owner. Incorrect measurement can result in performance issues, safety problems, and even damage to your car. In this Riverstone article, we explain in detail how tires are measured and what all those numbers and letters that appear on the sidewall of your tires mean.

The universal tire measurement code

Let's take as an example the following measurement that you might find on the sidewall of a tire: P225/65R17 95H

Let's break down each component:

1. Vehicle type (P)

The first letter indicates the type of vehicle for which the tire is designed:

• P: Passenger (passenger vehicle)
• LT: Light Truck
• ST: Special Trailer
• T: Temporary (temporary or spare tire)

If there is no letter, it is generally a European standard tire, which has different load capacities.

2. Section width (225)

The first number (in this case "225") indicates the width of the tire in millimeters, measured from wall to wall. This is the total width of the tire when mounted and inflated, but without load.

3. Aspect ratio or profile (65)

The number following the slash (in this case "65") represents the height of the tire sidewall as a percentage of the width. In our example, the sidewall height is 65% of 225 mm, which is approximately 146 mm.

A lower aspect ratio (such as 40 or 45) indicates a low profile, while higher numbers (such as 70 or 80) indicate a high profile.

4. Construction (R)

The letter indicates the type of internal construction of the tire:

• R: Radial (the layers run radially, perpendicular to the direction of rolling)
• D or -: Diagonal or conventional (less common in modern vehicles)
• B: Belted (combination of diagonal and radial construction, very uncommon)
• Today, almost all modern tires are of radial construction (R).

5. Rim diameter (17)

This number (in our example "17") indicates the diameter in inches of the rim or metal wheel on which the tire is mounted.

6. Load index (95)

This number represents the maximum load capacity that the tire can support. It does not directly indicate the weight in kilograms, but refers to a standardized table. In our example, "95" corresponds to a load capacity of 690 kg per tire.

Some common load indexes:

• 75 = 387 kg
• 85 = 515 kg
• 95 = 690 kg
• 100 = 800 kg
• 105 = 925 kg

7. Speed rating (H)

The last letter indicates the maximum speed at which the tire can operate safely under specific conditions:

• Q = up to 160 km/h
• S = up to 180 km/h
• T = up to 190 km/h
• H = up to 210 km/h
• V = up to 240 km/h
• W = up to 270 km/h
• Y = up to 300 km/h
• (Y) = above 300 km/h

In our example tire, the "H" indicates that it is designed to withstand speeds of up to 210 km/h.

Additional measurements you may find

In addition to the main nomenclature, you may find other specifications on your Riverstone tires:

Maximum load and pressure

Appears as "Max Load XXX kg (XXX lbs) at XXX kPa (XX psi)". Indicates the maximum weight the tire can support when inflated to the specified pressure.

DOT (Department of Transportation)

The DOT code includes information about the manufacturer, size, and more importantly, the date of manufacture. The last four numbers indicate the week and year of manufacture (for example, "1220" means the tire was manufactured in week 12 of the year 2020).

UTQG (Uniform Tire Quality Grading)

This rating system includes three categories:

• Wear: A comparative number indicating the expected useful life (e.g., 400, 500, etc.)
• Traction: Rated as AA, A, B or C, where AA is the best
• Temperature: Rated as A, B or C, where A is the best

How to physically measure your tires?

If you need to confirm the measurements of your current Riverstone tires and cannot read the information on the sidewall, you can perform these manual measurements:

For section width

Measure the distance from wall to wall at the widest part of the inflated tire (without load) using a ruler or measuring tape. Convert to millimeters if necessary.

For rim diameter

Measure from one end of the rim to the opposite end, passing through the center. This measurement will be in inches.

For aspect ratio

Measure the height of the sidewall from the edge of the rim to the outer surface of the tire. Divide this height by the section width and multiply by 100 to get the percentage.

Can I change the measurements of my tires?

It is possible to modify the original measurements of your tires, but you must maintain the same outer diameter to avoid problems with the speedometer, ABS, and other systems. For this, what is known as "tire equivalence" is used.

For example, a 225/65R17 tire could be replaced with a 235/60R17, since both have approximately the same total diameter.

Most common measurements according to vehicle type

Compact cars

• 175/65R14
• 185/60R15
• 195/55R16

Mid-size sedans

• 205/55R16
• 215/50R17
• 225/45R17

SUVs and crossovers

• 225/65R17
• 235/60R18
• 255/55R19

Trucks

• 245/70R17
• 265/65R18
• 275/60R20

How to find the recommended measurement for your vehicle?

The measurements recommended by the manufacturer can be found in:

• The owner's manual
• The label on the driver's door frame
• The fuel compartment cap
• Inside the glove compartment
• Riverstone always recommends respecting the manufacturer's specifications to ensure optimal performance and vehicle safety.