265/40R21 Tire Size in Inches and Millimeters

265/40R21 tires have a diameter of 29.3" (745 mm), a tread width of 10.4" (265 mm), and a wheel diameter of 21" (533.4 mm).The sidewall of the tire is 4.2" (106 mm), and the tire's circumference is 92" (2339.3 mm). This means a 265/40R21 tire will make make 689 revolutions per mile, or 427 revolutions per kilometer.

265/40R21 Tire Front
10.4"
29.3"
265/40R21 Tire Side
Tire Circumference
92"
21"
4.2"
689 Revs/Mile
SpecInchesMetric
Diameter29.3"745 mm
Width10.4"265 mm
Wheel21"533.4 mm
Sidewall4.2"106 mm
Circum92"2339.3 mm
Revolutions689 per mile427 per km

What Does 265/40R21 Mean?

The tire size 265/40R21 is a common size used on many trucks, SUVs, and other larger vehicles.

Here is what each part of the size designation represents:

  • 265: This number represents the width of the tire in millimeters. In this case, the tire is 265 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.
  • 21: 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 21-inch wheel.

265/40R21 tire size meaning

How To Convert 265/40R21 Into Inches

The 265/40R21 conversion is fairly simple. The first number in the tire size, 265, represents the width of the tire in millimeters. To convert this to inches, we divide 265 by 25.4 (since there are 25.4 millimeters in an inch). This gives us approximately 10.4 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 10.4 by 0.40, which gives us approximately 4.2 inches.

Finally, the last number in the tire size, 21, represents the diameter of the wheel rim in inches. Therefore, the tire size 265/40R21 can be expressed in inches as roughly 10.4 inches wide, 4.2 inches tall, and designed to fit a 21-inch wheel rim.

Frequently Asked Questions About 265/40R21 Tires

How tall is a 265/40R21 tire?

A 265/40R21 tire has an approximate height, also known as the overall diameter, of 29.3 inches (745 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 265/40R21 tire?

A 265/40R21 tire has a width of approximately 10.4 inches (265 millimeters). The width of the tire is the first number in the tire size designation, which in this case is “265”. 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 265/40R21 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
145/80R2029.1"740 mm20 mm
155/80R1928.8"731 mm19 mm
155/90R1829"737 mm18 mm
165/90R1728.7"730 mm17 mm
165/90R1829.7"755 mm18 mm
175/80R1829"737 mm18 mm
175/80R1930"763 mm19 mm
175/90R1729.4"748 mm17 mm
205/80R1628.9"734 mm16 mm
205/90R1529.6"751 mm15 mm
215/70R1728.9"734 mm17 mm
215/75R1628.7"728 mm16 mm
215/80R1528.5"725 mm15 mm
215/80R1629.5"750 mm16 mm
215/85R1529.4"747 mm15 mm
225/55R1928.8"731 mm19 mm
225/60R1828.6"727 mm18 mm
225/65R1728.5"724 mm17 mm
225/65R1829.5"749 mm18 mm
225/70R1729.4"748 mm17 mm
225/75R1629.3"744 mm16 mm
225/80R1529.2"741 mm15 mm
235/45R2129.3"745 mm21 mm
235/50R2029.3"744 mm20 mm
235/55R1929.2"741 mm19 mm
235/55R2030.2"766 mm20 mm
235/60R1829.1"739 mm18 mm
235/60R1930.1"765 mm19 mm
235/65R1729.1"738 mm17 mm
235/65R1830"763 mm18 mm
235/70R1629"736 mm16 mm
235/70R1730"762 mm17 mm
235/75R1528.9"733 mm15 mm
235/75R1629.8"758 mm16 mm
235/80R1529.8"757 mm15 mm
245/25R2428.8"732 mm24 mm
245/30R2429.8"758 mm24 mm
245/35R2228.8"731 mm22 mm
245/40R2128.7"729 mm21 mm
245/45R2028.7"728 mm20 mm
245/45R2129.6"753 mm21 mm
245/50R1928.7"729 mm19 mm
245/50R2029.7"754 mm20 mm
245/55R1828.6"727 mm18 mm
245/55R1929.6"753 mm19 mm
245/60R1728.6"726 mm17 mm
245/60R1829.6"751 mm18 mm
245/65R1729.5"750 mm17 mm
245/70R1528.5"725 mm15 mm
245/70R1629.5"750 mm16 mm
245/75R1529.5"749 mm15 mm
247/70R1629.6"752 mm16 mm
255/25R2429.1"738 mm24 mm
255/30R2430.1"764 mm24 mm
255/35R2229"737 mm22 mm
255/40R2129"737 mm21 mm
255/40R2230"763 mm22 mm
255/45R2029.1"738 mm20 mm
255/45R2130"763 mm21 mm
255/50R1929.1"739 mm19 mm
255/50R2030.1"764 mm20 mm
255/55R1829"737 mm18 mm
255/55R1930"763 mm19 mm
255/60R1729.1"738 mm17 mm
255/60R1830"763 mm18 mm
255/65R1629.1"738 mm16 mm
255/65R1730.1"764 mm17 mm
255/70R1529.1"739 mm15 mm
255/70R1630.1"764 mm16 mm
255/75R1530"763 mm15 mm
265/25R2429.2"742 mm24 mm
265/35R2229.3"745 mm22 mm
265/40R2129.3"745 mm21 mm
265/45R2029.4"746 mm20 mm
265/50R1828.5"723 mm18 mm
265/50R1929.5"749 mm19 mm
265/55R1728.5"724 mm17 mm
265/55R1829.5"749 mm18 mm
265/60R1628.5"724 mm16 mm
265/60R1729.5"750 mm17 mm
265/65R1629.5"750 mm16 mm
265/70R1529.6"753 mm15 mm
275/23R2429"736 mm24 mm
275/25R2429.4"748 mm24 mm
275/30R2228.5"725 mm22 mm
275/35R2128.5"725 mm21 mm
275/35R2229.6"751 mm22 mm
275/40R2028.7"728 mm20 mm
275/40R2129.6"753 mm21 mm
275/45R1928.8"731 mm19 mm
275/45R2029.8"756 mm20 mm
275/50R1828.9"733 mm18 mm
275/50R1929.9"759 mm19 mm
275/55R1728.9"734 mm17 mm
275/55R1829.9"759 mm18 mm
275/60R1629"736 mm16 mm
275/60R1730"762 mm17 mm
275/65R1630.1"764 mm16 mm
275/70R1530.2"767 mm15 mm
285/30R2228.8"731 mm22 mm
285/35R2128.9"733 mm21 mm
285/35R2229.9"759 mm22 mm
285/40R2029"736 mm20 mm
285/40R2130"761 mm21 mm
285/45R1929.1"739 mm19 mm
285/45R2030.1"764 mm20 mm
285/50R1829.3"743 mm18 mm
285/60R1629.4"748 mm16 mm
295/23R2429.4"746 mm24 mm
295/30R2229"737 mm22 mm
295/30R2330"762 mm23 mm
295/35R2129.1"739 mm21 mm
295/35R2230.1"765 mm22 mm
295/40R2029.3"744 mm20 mm
295/45R1828.5"723 mm18 mm
295/45R1929.5"749 mm19 mm
295/60R1528.9"735 mm15 mm
295/65R1530.1"765 mm15 mm
305/25R2329"736 mm23 mm
305/30R2229.3"743 mm22 mm
305/35R2129.4"747 mm21 mm
305/40R2029.6"752 mm20 mm
305/45R1828.8"731 mm18 mm
315/25R2329.2"742 mm23 mm
315/30R2128.5"723 mm21 mm
315/30R2229.5"749 mm22 mm
315/35R2028.7"728 mm20 mm
315/35R2129.6"753 mm21 mm
315/40R1928.9"735 mm19 mm
315/55R1629.6"752 mm16 mm
315/60R1529.9"759 mm15 mm
325/30R2128.7"729 mm21 mm
325/35R2029"736 mm20 mm
325/45R1829.5"749 mm18 mm
335/25R2228.6"727 mm22 mm
345/35R1928.5"725 mm19 mm
345/55R1530"761 mm15 mm