Tire Size Box

275/25R20 vs 275/30R20

275/30R20 compared with 275/25R20

+4.3% diameter, 0.0" width

275/30R20 is 26.50" tall vs 25.41". More than the 3% rule of thumb, so check carefully before switching.

25.4"20" rim2.7"10.8" wide
275/25R20 (solid) compared with 275/30R20 (dashed outline), drawn to scale

With 275/30R20 tires, when your speedometer says 60 mph you are really going

62.6 mph

275/30R20 is +1.08 inches (+4.3%) in overall diameter. That is more than the 3% most shops and makers recommend.

275/25R20275/30R20Difference%
Overall diameter25.41"26.50"+1.08"+4.3%
Section width10.83"10.83"0.00"0.0%
Sidewall height2.71"3.25"+0.54"+20.0%
Circumference79.84"83.24"+3.40"+4.3%
Revolutions per mile793.6761.2−32.4−4.1%

Speedometer difference

If your vehicle came with 275/25R20 and you fit 275/30R20, 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 mph41.7 mph+1.7 mph
50 mph52.1 mph+2.1 mph
60 mph62.6 mph+2.6 mph
65 mph67.8 mph+2.8 mph
70 mph73.0 mph+3.0 mph
75 mph78.2 mph+3.2 mph
80 mph83.4 mph+3.4 mph

Each size on its own

Questions

Which is bigger, 275/25R20 or 275/30R20?
275/30R20 is taller by 1.08 inches (26.50" vs 25.41"). 275/25R20 is the same width.
Can I replace 275/25R20 with 275/30R20?
It is not recommended without checking carefully. The diameter difference is +4.3%, 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 275/30R20 change my speedometer?
When your speedometer reads 60 mph with 275/30R20 fitted (calibrated for 275/25R20), your real speed is 62.6 mph. Your odometer will under-count miles by about 4.3%.
Will 275/30R20 lift my vehicle?
Ride height changes by half the diameter difference: +0.54 inches of ground clearance at the axle.

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