315/40R25 Tire Size in Inches and Millimeters

315/40R25 tires have a diameter of 34.9" (887 mm), a tread width of 12.4" (315 mm), and a wheel diameter of 25" (635 mm).The sidewall of the tire is 5" (126 mm), and the tire's circumference is 109.6" (2785.2 mm). This means a 315/40R25 tire will make make 578 revolutions per mile, or 359 revolutions per kilometer.

315/40R25 Tire Front
12.4"
34.9"
315/40R25 Tire Side
Tire Circumference
109.6"
25"
5"
578 Revs/Mile
SpecInchesMetric
Diameter34.9"887 mm
Width12.4"315 mm
Wheel25"635 mm
Sidewall5"126 mm
Circum109.6"2785.2 mm
Revolutions578 per mile359 per km

What Does 315/40R25 Mean?

The tire size 315/40R25 is a common size used on many trucks, SUVs, and other larger vehicles.

Here is what each part of the size designation represents:

  • 315: This number represents the width of the tire in millimeters. In this case, the tire is 315 millimeters wide.
  • 40: This number represents the aspect ratio of the tire, which is the height of the tire's sidewall as a percentage of its width. In this case, the sidewall height is 40% of the tire's width.
  • R: This letter indicates the tire's construction type. “R” stands for radial construction, which is the most common type of tire construction today.
  • 25: This number represents the diameter of the wheel that the tire is designed to fit on, in inches. In this case, the tire is designed to fit on a 25-inch wheel.

315/40R25 tire size meaning

How To Convert 315/40R25 Into Inches

The 315/40R25 conversion is fairly simple. The first number in the tire size, 315, represents the width of the tire in millimeters. To convert this to inches, we divide 315 by 25.4 (since there are 25.4 millimeters in an inch). This gives us approximately 12.4 inches.

The second number in the tire size, 40, represents the aspect ratio or the height of the tire as a percentage of its width. To calculate the height in inches, we multiply 12.4 by 0.40, which gives us approximately 5 inches.

Finally, the last number in the tire size, 25, represents the diameter of the wheel rim in inches. Therefore, the tire size 315/40R25 can be expressed in inches as roughly 12.4 inches wide, 5 inches tall, and designed to fit a 25-inch wheel rim.

Frequently Asked Questions About 315/40R25 Tires

How tall is a 315/40R25 tire?

A 315/40R25 tire has an approximate height, also known as the overall diameter, of 34.9 inches (887 mm). This height can vary slightly depending on the brand and model of the tire, as well as the amount of air pressure in the tire.

How wide is a 315/40R25 tire?

A 315/40R25 tire has a width of approximately 12.4 inches (315 millimeters). The width of the tire is the first number in the tire size designation, which in this case is “315”. It’s important to note that the actual width of the tire may vary slightly depending on the brand and model of the tire, and the width may also be affected by the amount of air pressure in the tire.

Understanding Tire Speed Ratings

When choosing the right tires for your vehicle, understanding the speed rating is crucial. But what exactly is a speed rating, and why does it matter?

What is a Tire Speed Rating?

A tire's speed rating indicates the maximum speed a tire can safely sustain over time. It's a manufacturer's assurance of tire performance, marked by a letter on the tire's sidewall. This rating is determined under controlled laboratory conditions and is part of a broader standard established by industry entities like the European Tyre and Rim Technical Organisation (ETRTO) and the U.S. Department of Transportation.

Common Speed Ratings Explained

  1. P-Rated: Up to 94 mph - Suitable for smaller sedans or light-duty vehicles.
  2. Q-Rated: Up to 100 mph - Often found on SUVs and light trucks with consistent highway use.
  3. R-Rated: Up to 106 mph - Typically for medium-duty trucks and vans.
  4. S-Rated: Up to 112 mph - Common for family sedans and larger vehicles with moderate performance.
  5. T-Rated: Up to 118 mph - Optimal for family vehicles, including minivans and some coupes.

Why is the Speed Rating Important?

The speed rating is not just about how fast you can legally drive; it's about safety and performance:
  • Ensures Safety: It guarantees that the tire can handle certain speeds without overheating and failing, which can prevent blowouts.
  • Optimizes Performance: Higher ratings often indicate better handling characteristics, important for maintaining vehicle stability.
  • Legal and Insurance Considerations: Matching the speed rating suggested by your vehicle manufacturer can be essential for insurance and warranty purposes.
When choosing tires, always refer to your vehicle’s manual to ensure compatibility. Remember, fitting tires with a lower speed rating than recommended can compromise safety and performance, while higher ratings might not provide extra benefits unless you frequently drive at high speeds. By understanding these nuances, you can make an informed choice that suits your driving habits while keeping safety a top priority.

Alternate 315/40R25 Replacement Tire Sizes

Upsizing your wheels or tires? Replacement tires must be within 3% of the diametor of the original tire. The following sizes fall within that range - click on any size to see detailed info about that tire and wheel combination.

SizeDiameterWidthWheel
275/25R3035.4"900 mm30 mm
275/55R2233.9"861 mm22 mm
275/65R2034.1"866 mm20 mm
275/80R1734.3"872 mm17 mm
275/80R1835.3"897 mm18 mm
285/55R2234.4"873 mm22 mm
285/65R2034.6"878 mm20 mm
285/75R1834.8"885 mm18 mm
295/45R2434.5"876 mm24 mm
295/55R2234.8"883 mm22 mm
295/60R2033.9"862 mm20 mm
295/65R2035.1"892 mm20 mm
295/70R1834.3"871 mm18 mm
295/75R1734.4"874 mm17 mm
305/35R2634.4"874 mm26 mm
305/45R2434.8"884 mm24 mm
305/50R2234.1"865 mm22 mm
305/55R2235.2"895 mm22 mm
305/60R2034.4"874 mm20 mm
305/70R1834.8"885 mm18 mm
305/75R1634"864 mm16 mm
315/20R3035"888 mm30 mm
315/40R2534.9"887 mm25 mm
315/40R2635.9"912 mm26 mm
315/45R2435.2"894 mm24 mm
315/50R2234.4"875 mm22 mm
315/60R2034.9"886 mm20 mm
315/70R1734.4"874 mm17 mm
315/70R1835.4"899 mm18 mm
315/75R1634.6"878 mm16 mm
325/45R2435.5"902 mm24 mm
325/50R2234.8"885 mm22 mm
325/60R2035.4"898 mm20 mm
325/65R1834.6"879 mm18 mm
325/70R1735"888 mm17 mm
335/35R2635.2"894 mm26 mm
335/40R2434.6"878 mm24 mm
335/55R2034.5"876 mm20 mm
335/70R1634.5"876 mm16 mm
345/60R1834.3"871 mm18 mm
355/40R2435.2"894 mm24 mm
355/50R2034"864 mm20 mm
355/70R1635.6"904 mm16 mm
375/40R2435.8"910 mm24 mm
375/45R2235.3"897 mm22 mm
375/60R1835.7"907 mm18 mm
375/65R1635.2"894 mm16 mm
385/35R2434.6"880 mm24 mm