255/40R21 tire size

A 255/40R21 tire is 29.03 in (737.4 mm) tall and 10.04 in (255.0 mm) wide, and turns 695 revolutions per mile.

• 29.03 inOverall diameter
• 4.02 inSidewall height
• 695Revolutions per mile
• 29.0x10.0R21Flotation equivalent

255/40R21 is a 21-inch tire with a 255 mm (10.04 in) section width and a 40% aspect ratio, giving a 4.02-inch sidewall and a flotation-style size of about 29.0x10.0R21.

Its overall diameter is 29.03 inches, so it rolls 91.2 inches per revolution and turns about 695 times per mile.

72 other sizes in this list are within 3% of that diameter.

Compare 255/40R21 with plausible swaps

• 225/55R19 vs 255/40R21 (−0.99%)
• 275/45R19 vs 255/40R21 (−0.99%)
• 255/50R19 vs 255/40R21 (+0.03%)
• 285/45R19 vs 255/40R21 (+0.23%)
• 235/55R19 vs 255/40R21 (+0.50%)
• 285/40R20 vs 255/40R21 (−0.19%)
• 255/45R20 vs 255/40R21 (+0.01%)
• 295/40R20 vs 255/40R21 (+0.90%)
• 255/35R21 vs 255/40R21 (−3.46%)
• 245/40R21 vs 255/40R21 (−1.08%)
• 285/35R21 vs 255/40R21 (−0.61%)
• 255/40R21 vs 295/35R21 (+0.34%)
• 255/40R21 vs 235/45R21 (+1.02%)
• 255/40R21 vs 265/40R21 (+1.08%)
• 255/40R21 vs 275/40R21 (+2.17%)
• 255/40R21 vs 255/45R21 (+3.46%)
• 255/40R21 vs 285/30R22 (−1.03%)
• 255/40R21 vs 245/35R22 (−0.96%)
• 255/40R21 vs 295/30R22 (−0.22%)
• 255/40R21 vs 255/35R22 (−0.01%)
• 255/40R21 vs 265/35R22 (+0.94%)

Sizes within 3% of 29.03 in diameter

• 235/65R17 29.03 in (−0.01%)
• 255/45R20 29.04 in (+0.01%)
• 255/35R22 29.03 in (−0.01%)
• 255/50R19 29.04 in (+0.03%)
• 255/55R18 29.04 in (+0.04%)
• 255/60R17 29.05 in (+0.05%)
• 255/65R16 29.05 in (+0.07%)
• 255/70R15 29.06 in (+0.08%)
• 285/40R20 28.98 in (−0.19%)
• 295/30R22 28.97 in (−0.22%)
• 285/45R19 29.10 in (+0.23%)
• 235/60R18 29.10 in (+0.24%)
• 235/70R16 28.95 in (−0.27%)
• 295/35R21 29.13 in (+0.34%)
• 235/55R19 29.18 in (+0.50%)
• 235/75R15 28.88 in (−0.53%)
• 285/35R21 28.85 in (−0.61%)
• 225/75R16 29.29 in (+0.88%)
• 295/40R20 29.29 in (+0.90%)
• 265/35R22 29.30 in (+0.94%)
• 245/35R22 28.75 in (−0.96%)
• 225/55R19 28.74 in (−0.99%)
• 275/45R19 28.74 in (−0.99%)
• 235/45R21 29.33 in (+1.02%)
• 285/30R22 28.73 in (−1.03%)
• 245/40R21 28.72 in (−1.08%)
• 265/40R21 29.35 in (+1.08%)
• 215/75R16 28.70 in (−1.15%)
• 245/45R20 28.68 in (−1.21%)
• 315/35R20 28.68 in (−1.21%)
• 325/30R21 28.68 in (−1.22%)
• 265/45R20 29.39 in (+1.23%)
• 275/40R20 28.66 in (−1.27%)
• 275/25R24 29.41 in (+1.32%)
• 245/50R19 28.65 in (−1.33%)
• 225/60R18 28.63 in (−1.38%)
• 265/50R19 29.43 in (+1.38%)
• 315/30R22 29.44 in (+1.41%)
• 245/55R18 28.61 in (−1.45%)
• 245/75R15 29.47 in (+1.51%)
• 275/35R21 28.58 in (−1.56%)
• 245/60R17 28.57 in (−1.57%)
• 245/70R16 29.50 in (+1.63%)
• 265/60R17 29.52 in (+1.68%)
• 245/65R16 28.54 in (−1.70%)
• 245/65R17 29.54 in (+1.75%)
• 225/65R17 28.52 in (−1.78%)
• 275/30R22 28.50 in (−1.84%)
• 245/60R18 29.57 in (+1.87%)
• 265/70R15 29.61 in (+1.98%)
• 305/40R20 29.61 in (+1.98%)
• 245/55R19 29.61 in (+1.99%)
• 265/50R18 28.43 in (−2.06%)
• 245/50R20 29.65 in (+2.12%)
• 225/70R16 28.40 in (−2.17%)
• 275/40R21 29.66 in (+2.17%)
• 265/45R19 28.39 in (−2.21%)
• 245/45R21 29.68 in (+2.24%)
• 315/35R21 29.68 in (+2.24%)
• 265/40R20 28.35 in (−2.36%)
• 235/45R20 28.33 in (−2.43%)
• 275/45R20 29.74 in (+2.45%)
• 265/35R21 28.30 in (−2.51%)
• 295/40R19 28.29 in (−2.55%)
• 225/75R15 28.29 in (−2.56%)
• 265/30R22 28.26 in (−2.66%)
• 235/50R19 28.25 in (−2.69%)
• 275/50R19 29.83 in (+2.74%)
• 285/35R22 29.85 in (+2.83%)
• 305/30R21 28.20 in (−2.85%)
• 235/75R16 29.88 in (+2.92%)
• 235/55R18 28.18 in (−2.94%)

Open 255/40R21 in the tire size calculator

Source: Calculated from standard tire geometry formulas. Verified 2026-09-27. How these numbers are calculated.