Tire Size Box

285/25R20 vs 285/30R20

285/30R20 compared with 285/25R20

+4.4% diameter, 0.0" width

285/30R20 is 26.73" tall vs 25.61". More than the 3% rule of thumb, so check carefully before switching.

25.6"20" rim2.8"11.2" wide
285/25R20 (solid) compared with 285/30R20 (dashed outline), drawn to scale

With 285/30R20 tires, when your speedometer says 60 mph you are really going

62.6 mph

285/30R20 is +1.12 inches (+4.4%) in overall diameter. That is more than the 3% most shops and makers recommend.

285/25R20285/30R20Difference%
Overall diameter25.61"26.73"+1.12"+4.4%
Section width11.22"11.22"0.00"0.0%
Sidewall height2.81"3.37"+0.56"+20.0%
Circumference80.46"83.98"+3.53"+4.4%
Revolutions per mile787.5754.4−33.1−4.2%

Speedometer difference

If your vehicle came with 285/25R20 and you fit 285/30R20, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.9 mph+0.9 mph
30 mph31.3 mph+1.3 mph
40 mph41.8 mph+1.8 mph
50 mph52.2 mph+2.2 mph
60 mph62.6 mph+2.6 mph
65 mph67.8 mph+2.8 mph
70 mph73.1 mph+3.1 mph
75 mph78.3 mph+3.3 mph
80 mph83.5 mph+3.5 mph

Each size on its own

Questions

Which is bigger, 285/25R20 or 285/30R20?
285/30R20 is taller by 1.12 inches (26.73" vs 25.61"). 285/25R20 is the same width.
Can I replace 285/25R20 with 285/30R20?
It is not recommended without checking carefully. The diameter difference is +4.4%, 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 285/30R20 change my speedometer?
When your speedometer reads 60 mph with 285/30R20 fitted (calibrated for 285/25R20), your real speed is 62.6 mph. Your odometer will under-count miles by about 4.4%.
Will 285/30R20 lift my vehicle?
Ride height changes by half the diameter difference: +0.56 inches of ground clearance at the axle.

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