185/45R15 Tire Size in Inches and Millimeters

185/45R15 tires have a diameter of 21.5" (547 mm), a tread width of 7.3" (185 mm), and a wheel diameter of 15" (381 mm).The sidewall of the tire is 3.3" (83 mm), and the tire's circumference is 67.5" (1717.6 mm). This means a 185/45R15 tire will make make 939 revolutions per mile, or 582 revolutions per kilometer.

185/45R15 Tire Front
7.3"
21.5"
185/45R15 Tire Side
Tire Circumference
67.5"
15"
3.3"
939 Revs/Mile
SpecInchesMetric
Diameter21.5"547 mm
Width7.3"185 mm
Wheel15"381 mm
Sidewall3.3"83 mm
Circum67.5"1717.6 mm
Revolutions939 per mile582 per km

What Does 185/45R15 Mean?

The tire size 185/45R15 is a common size used on many trucks, SUVs, and other larger vehicles.

Here is what each part of the size designation represents:

  • 185: This number represents the width of the tire in millimeters. In this case, the tire is 185 millimeters wide.
  • 45: 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 45% 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.
  • 15: 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 15-inch wheel.

185/45R15 tire size meaning

How To Convert 185/45R15 Into Inches

The 185/45R15 conversion is fairly simple. The first number in the tire size, 185, represents the width of the tire in millimeters. To convert this to inches, we divide 185 by 25.4 (since there are 25.4 millimeters in an inch). This gives us approximately 7.3 inches.

The second number in the tire size, 45, represents the aspect ratio or the height of the tire as a percentage of its width. To calculate the height in inches, we multiply 7.3 by 0.45, which gives us approximately 3.3 inches.

Finally, the last number in the tire size, 15, represents the diameter of the wheel rim in inches. Therefore, the tire size 185/45R15 can be expressed in inches as roughly 7.3 inches wide, 3.3 inches tall, and designed to fit a 15-inch wheel rim.

Frequently Asked Questions About 185/45R15 Tires

How tall is a 185/45R15 tire?

A 185/45R15 tire has an approximate height, also known as the overall diameter, of 21.5 inches (547 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 185/45R15 tire?

A 185/45R15 tire has a width of approximately 7.3 inches (185 millimeters). The width of the tire is the first number in the tire size designation, which in this case is “185”. 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 185/45R15 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
115/70R1521.4"543 mm15 mm
125/70R1420.9"532 mm14 mm
125/70R1521.9"557 mm15 mm
135/80R1321.5"546 mm13 mm
145/65R1421.4"544 mm14 mm
145/70R1321"534 mm13 mm
145/80R1221.1"537 mm12 mm
145/80R1322.1"562 mm13 mm
155/65R1320.9"532 mm13 mm
155/65R1422"558 mm14 mm
155/70R1321.6"548 mm13 mm
155/80R1221.8"553 mm12 mm
165/40R1621.2"538 mm16 mm
165/45R1621.8"554 mm16 mm
165/50R1521.5"547 mm15 mm
165/55R1421.2"538 mm14 mm
165/55R1522.2"563 mm15 mm
165/60R1421.8"554 mm14 mm
165/65R1321.4"544 mm13 mm
165/70R1221.1"537 mm12 mm
165/70R1322.1"562 mm13 mm
175/50R1420.9"532 mm14 mm
175/50R1521.9"557 mm15 mm
175/60R1321.3"540 mm13 mm
175/65R1322"558 mm13 mm
185/45R1521.5"547 mm15 mm
185/50R1421.3"542 mm14 mm
185/55R1321"534 mm13 mm
185/55R1422"560 mm14 mm
185/60R1321.7"552 mm13 mm
195/40R1622.1"562 mm16 mm
195/45R1420.9"532 mm14 mm
195/45R1521.9"557 mm15 mm
195/55R1321.4"544 mm13 mm
205/45R1421.3"540 mm14 mm
205/50R1321.1"536 mm13 mm
205/50R1422.1"562 mm14 mm
215/35R1621.9"556 mm16 mm
215/40R1521.8"553 mm15 mm
215/50R1321.5"546 mm13 mm
225/40R1421.1"536 mm14 mm
225/45R1320.9"532 mm13 mm
225/45R1422"558 mm14 mm
225/50R1321.9"556 mm13 mm
245/35R1521.8"553 mm15 mm
255/35R1421"534 mm14 mm
255/40R1321"534 mm13 mm