355/25R21 Tire Size in Inches & Millimeters

Tire size “355/25R21” indicates your vehicle’s specifications based on tire width, aspect ratio, height, tire construction, diameter, radial and inches. These tire size numbers represent our tire sizes in both Metric (in millimeters) and Imperial (in inches) units of measurement to help find the correct tire size for your vehicle.

To convert tire size 355/25R21 to inches, you must know what these numbers represent.

So let us know 355/25R21 in simple words:

First number “355” indicates the tire’s width in millimeters.
Second number “25” refers to the aspect ratio, which is the height of the tire’s sidewall as a percentage of its width.
Third number “R21” refers to a tire that is designed to fit a 21-inch diameter rim.

Therefore, when converting the tire size 355/25R21 to inches, it can be concluded that the width of the tire will be approximately 14 inches ( 355 mm= 14 in), and the sidewall height will be approximately 3.5 inches (25% of 14 inches = 3.5 inches).

How to convert 355/25R21 into Inches (imperial)?

To convert tire size 355/25R21 to inches (Imperial) –

1. Width conversion: To convert it to inches, you can use a conversion factor of approximately 25.4 millimeters per inch.

  • 355 millimeters/25.4 = approximately 14 inches
    So, the width of the tire is approximately 14 inches.

2. Aspect Ratio Calculation: To calculate sidewall height in inches, you can use the tire width (from Step 1) and the aspect ratio:

  • Sidewall Height = Width (in inches) * Aspect Ratio / 100
  • Sidewall Height = 14 inches * 25/100 = approximately 3.5 inches
    So, the tire sidewall height is approximately 3.5 inches.

3. Rim Diameter: The “R” in the tire size stands for “radial construction” and the last number “21” indicates the rim diameter in inches. In this case, it’s already in inches.
So, the converted tire size “355/25R21” in inches (imperial) is approximately:

  • Width: 14 inches
  • Sidewall Height: 3.5 inches
  • Rim Diameter: 21 inches

How to convert 355/25R21 into Millimeters (metric)?

To convert the tire size 355/25R21 into millimeters (metric) –

1. Width Conversion: The first number in the tire size, “355“, represents the tire’s width in millimeters. Since it’s already in millimeters, there’s no need for conversion.

  • Width: 355millimeters

2. Aspect Ratio Calculation: The second number “25” is the aspect ratio, representing the tire’s sidewall height as a percentage of its width. To calculate the sidewall height in millimeters, you can use the tire’s width (from step 1) and the aspect ratio:

  • Sidewall height = Width (in millimeters) * Aspect Ratio / 100
  • Sidewall height = 355 millimeters * 25 / 100 = 89 mm millimeters
    So, the tire’s sidewall height is approximately 89 mm millimeters.

3. Rim Diameter: The “R” in the tire size stands for “radial construction” and the last number, “21” indicates the rim diameter in inches. To convert this to millimeters, you can use the conversion factor of approximately 25.4 millimeters per inch.

  • Rim diameter = 21 inches * 25.4 millimeters per inch = 533 mm millimeters
    So, the rim diameter is approximately 533 mm millimeters.

So, the converted tire size “355/25R21” in millimeters (metric) is approximately:

  • Width: 355 mm
  • Sidewall Height: 89 mm
  • Rim Diameter: 533 mm

Alternate Tire Size of 355/25R21 For replacement

Tire Size Overall Diameter Difference
265/25R22 27.2″ (691 mm) -2.8%
265/30R21 27.3″ (693 mm) -2.5%
225/30R22 27.4″ (695 mm) -2.3%
325/25R21 27.4″ (695 mm) -2.3%
235/35R21 27.4″ (697 mm) -2%
275/25R22 27.4″ (697 mm) -2%
275/30R21 27.5″ (699 mm) -1.7%
285/25R22 27.6″ (701 mm) -1.4%
235/30R22 27.6″ (701 mm) -1.4%
245/35R21 27.8″ (705 mm) -0.8%
285/30R21 27.8″ (705 mm) -0.8%
245/30R22 27.8″ (707 mm) -0.6%
295/25R22 27.8″ (707 mm) -0.6%
295/30R21 28″ (711 mm) 0%
305/25R22 28″ (711 mm) 0%
255/35R21 28″ (711 mm) 0%
255/30R22 28.1″ (713 mm) 0.3%
265/25R23 28.2″ (716 mm) 0.7%
315/25R22 28.2″ (717 mm) 0.8%
305/30R21 28.2″ (717 mm) 0.8%
265/35R21 28.3″ (719 mm) 1.1%
265/30R22 28.3″ (719 mm) 1.1%
315/30R21 28.5″ (723 mm) 1.7%
275/35R21 28.5″ (725 mm) 2%
275/30R22 28.5″ (725 mm) 2%
335/25R22 28.6″ (727 mm) 2.3%
245/40R21 28.7″ (729 mm) 2.5%
325/30R21 28.7″ (729 mm) 2.5%
245/35R22 28.8″ (731 mm) 2.8%
285/30R22 28.8″ (731 mm) 2.8%

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