The ultimate tire calculator – calculate dimensions

More than just rubber: Understand and calculate your tire dimensions

Have you ever looked at the numbers on the sidewall of your car tire – for example , 225/45 R17 – and wondered what they actually mean? This combination of numbers and letters isn't a secret code, but rather the precise blueprint of your tire. Understanding these dimensions is crucial when buying new rims, changing tire sizes, or simply out of curiosity.

In this article, we not only unlock the secret behind tire dimensions, but also provide you with an interactive calculator so you can calculate everything yourself!

The anatomy of a tire size: What do the numbers mean?

Let's take our example 225/45 R17 and break it down:

225 (tire width): The first number indicates the nominal width of the tire in millimeters . Our tire is therefore 225 mm wide.

45 (aspect ratio): The second number is not a direct length measurement, but a percentage ratio . It describes the height of the tire sidewall (the side part of the tire) in relation to the tire width. In our case, the sidewall height is 45% of 225 mm.

R (design): The "R" stands for radial tires , which are now standard on almost all passenger cars.

17 (rim diameter): The last number indicates the diameter of the rim the tire fits. This measurement is given in inches . Our tire therefore fits a 17-inch rim.

The calculation in detail

With these three values, we can now calculate interesting measurements:

• Sidewall height: How high is the tire from the rim to the tread?

  • Formula: (Tire width × Aspect ratio) / 100
  • Example: (225 mm × 45) / 100 = 101.25 mm

• Overall diameter of the wheel: What is the diameter of the wheel from one end to the other?

  • Formula: (sidewall height × 2) + rim diameter in mm
  • Important: We need to convert the rim diameter from inches to millimeters (1 inch = 25.4 mm).
  • Example: (101.25 mm × 2) + (17 inches × 25.4) = 202.5 mm + 431.8 mm = 634.3 mm

• Rolling circumference: What distance does the tire travel in one full revolution? This is particularly important for assessing speedometer deviations when changing tire sizes.

  • Formula: Total diameter × π (Pi ≈ 3.14159)
  • Example: 634.3 mm × π ≈ 1992.7 mm or approx. 1.99 meters .

Why is this important?

Changing your tire size will change the rolling circumference.

• Larger range: Your speedometer shows a lower speed than you are actually driving.
• Smaller gauge: Your speedometer shows a higher speed than you are actually driving.

Legally, only minor deviations are permitted. Our calculator allows you to compare different tire sizes and ensure you remain within legal and safe limits.