Tire Size Box

285/55R18 vs 285/65R18

285/65R18 compared with 285/55R18

+7.4% diameter, 0.0" width

285/65R18 is 32.59" tall vs 30.34". More than the 3% rule of thumb, so check carefully before switching.

30.3"18" rim6.2"11.2" wide
285/55R18 (solid) compared with 285/65R18 (dashed outline), drawn to scale

With 285/65R18 tires, when your speedometer says 60 mph you are really going

64.4 mph

285/65R18 is +2.24 inches (+7.4%) in overall diameter. That is more than the 3% most shops and makers recommend.

285/55R18285/65R18Difference%
Overall diameter30.34"32.59"+2.24"+7.4%
Section width11.22"11.22"0.00"0.0%
Sidewall height6.17"7.29"+1.12"+18.2%
Circumference95.32"102.37"+7.05"+7.4%
Revolutions per mile664.7618.9−45.8−6.9%

Speedometer difference

If your vehicle came with 285/55R18 and you fit 285/65R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.5 mph+1.5 mph
30 mph32.2 mph+2.2 mph
40 mph43.0 mph+3.0 mph
50 mph53.7 mph+3.7 mph
60 mph64.4 mph+4.4 mph
65 mph69.8 mph+4.8 mph
70 mph75.2 mph+5.2 mph
75 mph80.5 mph+5.5 mph
80 mph85.9 mph+5.9 mph

Each size on its own

Questions

Which is bigger, 285/55R18 or 285/65R18?
285/65R18 is taller by 2.24 inches (32.59" vs 30.34"). 285/55R18 is the same width.
Can I replace 285/55R18 with 285/65R18?
It is not recommended without checking carefully. The diameter difference is +7.4%, 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 285/65R18 change my speedometer?
When your speedometer reads 60 mph with 285/65R18 fitted (calibrated for 285/55R18), your real speed is 64.4 mph. Your odometer will under-count miles by about 7.4%.
Will 285/65R18 lift my vehicle?
Ride height changes by half the diameter difference: +1.12 inches of ground clearance at the axle.

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