Tire Size Calculator

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Stock Sizes

  • 255/75-16

Plus Sizes

  • 255/75-16

Accepts P-Metric and Inches
/ R
/ R
40/12.5r20 vs 320/90r20 Tire Comparison Side By Side
  40/12.5-20 320/90-20 Difference
Diameter inches (mm) 40.03 (1016.8) 42.68 (1084) 2.65 (67.2) 6.6%
Width inches (mm) 12.52 (318) 12.6 (320) 0.08 (2) 0.6%
Circum. inches (mm) 125.76 (3194.37) 134.07 (3405.49) 8.31 (211.12) 6.6%
Sidewall Height inches (mm) 10.02 (254.4) 11.34 (288) 1.32 (33.6) 13.2%
Revolutions per mile (km) 503.81 (313.05) 472.57 (293.64) -31.23 (-19.41) -6.2%

Speedometer Difference

Speedo Reading Actual Speed
20 mph (32.19 km/h)21.32 mph (34.31 km/h)
25 mph (40.23 km/h)26.65 mph (42.89 km/h)
30 mph (48.28 km/h)31.98 mph (51.47 km/h)
35 mph (56.33 km/h)37.31 mph (60.05 km/h)
40 mph (64.37 km/h)42.64 mph (68.63 km/h)
45 mph (72.42 km/h)47.97 mph (77.21 km/h)
50 mph (80.47 km/h)53.3 mph (85.79 km/h)
55 mph (88.51 km/h)58.63 mph (94.36 km/h)
60 mph (96.56 km/h)63.97 mph (102.94 km/h)
65 mph (104.61 km/h)69.3 mph (111.52 km/h)
70 mph (112.65 km/h)74.63 mph (120.1 km/h)
75 mph (120.7 km/h)79.96 mph (128.68 km/h)
80 mph (128.75 km/h)85.29 mph (137.26 km/h)
85 mph (136.79 km/h)90.62 mph (145.84 km/h)
90 mph (144.84 km/h)95.95 mph (154.41 km/h)
95 mph (152.89 km/h)101.28 mph (162.99 km/h)
100 mph (160.93 km/h)106.61 mph (171.57 km/h)

Gear Ratio / RPMs for New Tire (@ 65 mph)
2.35 2.73 2.94 3.07 3.21 3.31 3.42 3.55 3.73 3.91 4.11 4.27 4.56 4.88 5.13 5.29 5.38 5.71 6.17 7.17
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