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255/40R21 Tire Size
All You Need to Know About 255/40R21 Tires
255/40R21 tires have a section width of 255 millimeters (mm), an aspect ratio of 40%, radial construction, and a 21-inch wheel diameter. Before buying tires sized 255/40R21, converting 255/40R21 measurements into inches, comparing them with similar tire sizes such as 255/35R21 and 265/40R21, and understanding interchangeability limits helps drivers confirm proper fitment and avoid calibration or clearance issues.
What Are the Dimensions of a 255/40R21 Tire in Inches?
A 255/40R21 tire has a section width of 10.04 inches (≈ 10.0") and a sidewall height of 4.02 inches (≈ 4.0"). The overall diameter of a 255/40R21 tire is 29.03 inches (≈ 29.0"), and the circumference is approximately 91.21 inches (≈ 91.2"). The recommended rim width range for the 255/40R21 size is 8.5 to 10.0 inches.
In inches, the 255/40R21 tire size can be represented as 29.0" × 10.0" R21.
How tall and wide are 255/40R21 tires?
A 255/40R21 tire is approximately 29.03 inches (737.40 mm) tall and 10.04 inches (255 mm) wide.
Comparison of 255/40R21 With Similar Tire Sizes
Comparing 255/40R21 with 255/35R21 and 265/40R21 highlights how changes in aspect ratio and width affect ride height, speedometer accuracy, and suitability as a replacement.
What Is the Difference Between 255/40R21 vs 255/35R21?
The main difference between 255/40R21 and 255/35R21 is the aspect ratio, which directly impacts sidewall height and overall diameter. Both tires share the same width and rim diameter. The 255/40R21 has a sidewall height of 102.00 mm (≈ 4.02") and an overall diameter of 737.40 mm (≈ 29.03"). The 255/35R21 has a sidewall height of 89.25 mm (≈ 3.51") and an overall diameter of 711.90 mm (≈ 28.03").
This means the 255/40R21 has a 12.75 mm (≈ 0.50") taller sidewall and is 25.50 mm (≈ 1.00") larger overall.
Tire Size Comparison Table
Tire Dimension | 255/40R21 (mm & in) | 255/35R21 (mm & in) | Difference (mm & in) | Percentage Difference |
Section Width | 255 mm (≈ 10.04") | 255 mm (≈ 10.04") | 0 | 0% |
Sidewall Height | 102.00 mm (≈ 4.02") | 89.25 mm (≈ 3.51") | 12.75 mm (≈ 0.50") | ≈ 14.3% |
Overall Diameter | 737.40 mm (≈ 29.03") | 711.90 mm (≈ 28.03") | 25.50 mm (≈ 1.00") | ≈ 3.46% |
Circumference | 2316.61 mm (≈ 91.21") | 2236.50 mm (≈ 88.05") | 80.11 mm (≈ 3.15") | ≈ 3.46% |
Radius | 368.70 mm (≈ 14.52") | 355.95 mm (≈ 14.01") | 12.75 mm (≈ 0.50") | ≈ 3.46% |
Rim Diameter | 533.4 mm (21") | 533.4 mm (21") | — | — |
Recommended Rim Width | 8.5–10.0" | 8.5–10.0" | — | — |
Can I use 255/35R21 instead of 255/40R21?
This is a marginal downgrade rather than a direct substitute. The overall diameter decreases by ≈ 3.5%, which slightly exceeds the commonly cited ±3% guideline. While the tire fits the same 21-inch wheels, the smaller diameter will cause the speedometer to read fast (If your speedometer reads 60 mph, you are actually going roughly 57.9 mph), lower ride height (your vehicle will sit exactly 0.51 inches lower to the ground, which may be a concern for clearing speed bumps or steep driveways), and firm up ride quality due to the shorter sidewall. This change may work for some drivers seeking a sharper response, but manufacturer specifications and clearance should be checked before switching.
The Load Index is the biggest safety risk here.
- A 255/40R21 usually has a load index of 102 (1,874 lbs).
- A 255/35R21 often drops to a load index of 98 (1,653 lbs).
If your vehicle's door placard requires a load rating of 102, the 255/35R21 would be unsafe to use because it cannot technically support the vehicle's maximum gross weight.
What Is the Difference Between 255/40R21 vs 265/40R21?
The main difference between 255/40R21 and 265/40R21 is the section width. Both tires share the same aspect ratio and rim diameter, but the wider tire has a slightly taller overall diameter.
The 255/40R21 is 255 mm wide with an overall diameter of 737.40 mm (≈ 29.03").
The 265/40R21 is 265 mm wide, has a sidewall height of 106.00 mm (≈ 4.17"), and an overall diameter of 745.40 mm (≈ 29.35").
This means the 265/40R21 is 10 mm wider, has a 4.00 mm (≈ 0.16") taller sidewall, and is 8.00 mm (≈ 0.31") larger overall.
255/40R21 vs 265/40R21 Tire Size Comparison Table
Tire Dimension | 255/40R21 (mm & in) | 265/40R21 (mm & in) | Difference (mm & in) | Percentage Difference |
Section Width | 255 mm (≈ 10.04") | 265 mm (≈ 10.43") | 10 mm (≈ 0.39") | ≈ 3.9% |
Sidewall Height | 102.00 mm (≈ 4.02") | 106.00 mm (≈ 4.17") | 4.00 mm (≈ 0.16") | ≈ 3.9% |
Overall Diameter | 737.40 mm (≈ 29.03") | 745.40 mm (≈ 29.35") | 8.00 mm (≈ 0.31") | ≈ 1.08% |
Circumference | 2316.61 mm (≈ 91.21") | 2341.74 mm (≈ 92.19") | 25.13 mm (≈ 0.99") | ≈ 1.08% |
Radius | 368.70 mm (≈ 14.52") | 372.70 mm (≈ 14.67") | 4.00 mm (≈ 0.16") | ≈ 1.08% |
Rim Diameter | 533.4 mm (21") | 533.4 mm (21") | — | — |
Recommended Rim Width | 8.5–10.0" | 9.0–10.5" | — | — |
Can I use 265/40R21 instead of 255/40R21?
Yes, this is generally a straightforward and well-within-tolerance alternative. The overall diameter difference is only ≈ 1.1%, so speedometer accuracy and vehicle calibration remain very close to stock. The added width may slightly increase grip and steering effort, but as long as wheel width and fender clearance are adequate, this swap is typically trouble-free.
Recommended 265/40R21 Tires
If you plan to switch to 265/40R21 instead of 255/40R21, well-regarded options in this size include:
All You Need to Know About 255/40R21 Tires
255/40R21 tires have a section width of 255 millimeters (mm), an aspect ratio of 40%, radial construction, and a 21-inch wheel diameter. Before buying tires sized 255/40R21, converting 255/40R21 measurements into inches, comparing them with similar tire sizes such as 255/35R21 and 265/40R21, and understanding interchangeability limits helps drivers confirm proper fitment and avoid calibration or clearance issues.
What Are the Dimensions of a 255/40R21 Tire in Inches?
A 255/40R21 tire has a section width of 10.04 inches (≈ 10.0") and a sidewall height of 4.02 inches (≈ 4.0"). The overall diameter of a 255/40R21 tire is 29.03 inches (≈ 29.0"), and the circumference is approximately 91.21 inches (≈ 91.2"). The recommended rim width range for the 255/40R21 size is 8.5 to 10.0 inches.
In inches, the 255/40R21 tire size can be represented as 29.0" × 10.0" R21.
How tall and wide are 255/40R21 tires?
A 255/40R21 tire is approximately 29.03 inches (737.40 mm) tall and 10.04 inches (255 mm) wide.
Comparison of 255/40R21 With Similar Tire Sizes
Comparing 255/40R21 with 255/35R21 and 265/40R21 highlights how changes in aspect ratio and width affect ride height, speedometer accuracy, and suitability as a replacement.
What Is the Difference Between 255/40R21 vs 255/35R21?
The main difference between 255/40R21 and 255/35R21 is the aspect ratio, which directly impacts sidewall height and overall diameter. Both tires share the same width and rim diameter. The 255/40R21 has a sidewall height of 102.00 mm (≈ 4.02") and an overall diameter of 737.40 mm (≈ 29.03"). The 255/35R21 has a sidewall height of 89.25 mm (≈ 3.51") and an overall diameter of 711.90 mm (≈ 28.03").
This means the 255/40R21 has a 12.75 mm (≈ 0.50") taller sidewall and is 25.50 mm (≈ 1.00") larger overall.
Tire Size Comparison Table
Tire Dimension | 255/40R21 (mm & in) | 255/35R21 (mm & in) | Difference (mm & in) | Percentage Difference |
Section Width | 255 mm (≈ 10.04") | 255 mm (≈ 10.04") | 0 | 0% |
Sidewall Height | 102.00 mm (≈ 4.02") | 89.25 mm (≈ 3.51") | 12.75 mm (≈ 0.50") | ≈ 14.3% |
Overall Diameter | 737.40 mm (≈ 29.03") | 711.90 mm (≈ 28.03") | 25.50 mm (≈ 1.00") | ≈ 3.46% |
Circumference | 2316.61 mm (≈ 91.21") | 2236.50 mm (≈ 88.05") | 80.11 mm (≈ 3.15") | ≈ 3.46% |
Radius | 368.70 mm (≈ 14.52") | 355.95 mm (≈ 14.01") | 12.75 mm (≈ 0.50") | ≈ 3.46% |
Rim Diameter | 533.4 mm (21") | 533.4 mm (21") | — | — |
Recommended Rim Width | 8.5–10.0" | 8.5–10.0" | — | — |
Can I use 255/35R21 instead of 255/40R21?
This is a marginal downgrade rather than a direct substitute. The overall diameter decreases by ≈ 3.5%, which slightly exceeds the commonly cited ±3% guideline. While the tire fits the same 21-inch wheels, the smaller diameter will cause the speedometer to read fast (If your speedometer reads 60 mph, you are actually going roughly 57.9 mph), lower ride height (your vehicle will sit exactly 0.51 inches lower to the ground, which may be a concern for clearing speed bumps or steep driveways), and firm up ride quality due to the shorter sidewall. This change may work for some drivers seeking a sharper response, but manufacturer specifications and clearance should be checked before switching.
The Load Index is the biggest safety risk here.
- A 255/40R21 usually has a load index of 102 (1,874 lbs).
- A 255/35R21 often drops to a load index of 98 (1,653 lbs).
If your vehicle's door placard requires a load rating of 102, the 255/35R21 would be unsafe to use because it cannot technically support the vehicle's maximum gross weight.
What Is the Difference Between 255/40R21 vs 265/40R21?
The main difference between 255/40R21 and 265/40R21 is the section width. Both tires share the same aspect ratio and rim diameter, but the wider tire has a slightly taller overall diameter.
The 255/40R21 is 255 mm wide with an overall diameter of 737.40 mm (≈ 29.03").
The 265/40R21 is 265 mm wide, has a sidewall height of 106.00 mm (≈ 4.17"), and an overall diameter of 745.40 mm (≈ 29.35").
This means the 265/40R21 is 10 mm wider, has a 4.00 mm (≈ 0.16") taller sidewall, and is 8.00 mm (≈ 0.31") larger overall.
255/40R21 vs 265/40R21 Tire Size Comparison Table
Tire Dimension | 255/40R21 (mm & in) | 265/40R21 (mm & in) | Difference (mm & in) | Percentage Difference |
Section Width | 255 mm (≈ 10.04") | 265 mm (≈ 10.43") | 10 mm (≈ 0.39") | ≈ 3.9% |
Sidewall Height | 102.00 mm (≈ 4.02") | 106.00 mm (≈ 4.17") | 4.00 mm (≈ 0.16") | ≈ 3.9% |
Overall Diameter | 737.40 mm (≈ 29.03") | 745.40 mm (≈ 29.35") | 8.00 mm (≈ 0.31") | ≈ 1.08% |
Circumference | 2316.61 mm (≈ 91.21") | 2341.74 mm (≈ 92.19") | 25.13 mm (≈ 0.99") | ≈ 1.08% |
Radius | 368.70 mm (≈ 14.52") | 372.70 mm (≈ 14.67") | 4.00 mm (≈ 0.16") | ≈ 1.08% |
Rim Diameter | 533.4 mm (21") | 533.4 mm (21") | — | — |
Recommended Rim Width | 8.5–10.0" | 9.0–10.5" | — | — |
Can I use 265/40R21 instead of 255/40R21?
Yes, this is generally a straightforward and well-within-tolerance alternative. The overall diameter difference is only ≈ 1.1%, so speedometer accuracy and vehicle calibration remain very close to stock. The added width may slightly increase grip and steering effort, but as long as wheel width and fender clearance are adequate, this swap is typically trouble-free.
Recommended 265/40R21 Tires
If you plan to switch to 265/40R21 instead of 255/40R21, well-regarded options in this size include:
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