Tire Size Box

285/55R20 vs 285/65R20

285/65R20 compared with 285/55R20

+6.9% diameter, 0.0" width

285/65R20 is 34.59" tall vs 32.34". More than the 3% rule of thumb, so check carefully before switching.

32.3"20" rim6.2"11.2" wide
285/55R20 (solid) compared with 285/65R20 (dashed outline), drawn to scale

With 285/65R20 tires, when your speedometer says 60 mph you are really going

64.2 mph

285/65R20 is +2.24 inches (+6.9%) in overall diameter. That is more than the 3% most shops and makers recommend.

285/55R20285/65R20Difference%
Overall diameter32.34"34.59"+2.24"+6.9%
Section width11.22"11.22"0.00"0.0%
Sidewall height6.17"7.29"+1.12"+18.2%
Circumference101.61"108.66"+7.05"+6.9%
Revolutions per mile623.6583.1−40.5−6.5%

Speedometer difference

If your vehicle came with 285/55R20 and you fit 285/65R20, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.4 mph+1.4 mph
30 mph32.1 mph+2.1 mph
40 mph42.8 mph+2.8 mph
50 mph53.5 mph+3.5 mph
60 mph64.2 mph+4.2 mph
65 mph69.5 mph+4.5 mph
70 mph74.9 mph+4.9 mph
75 mph80.2 mph+5.2 mph
80 mph85.6 mph+5.6 mph

Each size on its own

Questions

Which is bigger, 285/55R20 or 285/65R20?
285/65R20 is taller by 2.24 inches (34.59" vs 32.34"). 285/55R20 is the same width.
Can I replace 285/55R20 with 285/65R20?
It is not recommended without checking carefully. The diameter difference is +6.9%, more than the 3% most shops and makers allow. It will throw off the speedometer and may affect ABS, stability control and clearance.
How much will 285/65R20 change my speedometer?
When your speedometer reads 60 mph with 285/65R20 fitted (calibrated for 285/55R20), your real speed is 64.2 mph. Your odometer will under-count miles by about 6.9%.
Will 285/65R20 lift my vehicle?
Ride height changes by half the diameter difference: +1.12 inches of ground clearance at the axle.

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