Tire Size Box

265/25R20 vs 255/30R20

255/30R20 compared with 265/25R20

+3.2% diameter, −0.4" width

255/30R20 is 26.02" tall vs 25.22". More than the 3% rule of thumb, so check carefully before switching.

25.2"20" rim2.6"10.4" wide
265/25R20 (solid) compared with 255/30R20 (dashed outline), drawn to scale

With 255/30R20 tires, when your speedometer says 60 mph you are really going

61.9 mph

255/30R20 is +0.81 inches (+3.2%) in overall diameter. That is more than the 3% most shops and makers recommend.

265/25R20255/30R20Difference%
Overall diameter25.22"26.02"+0.81"+3.2%
Section width10.43"10.04"−0.39"−3.8%
Sidewall height2.61"3.01"+0.40"+15.5%
Circumference79.22"81.76"+2.54"+3.2%
Revolutions per mile799.8775.0−24.8−3.1%

Speedometer difference

If your vehicle came with 265/25R20 and you fit 255/30R20, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.6 mph+0.6 mph
30 mph31.0 mph+1.0 mph
40 mph41.3 mph+1.3 mph
50 mph51.6 mph+1.6 mph
60 mph61.9 mph+1.9 mph
65 mph67.1 mph+2.1 mph
70 mph72.2 mph+2.2 mph
75 mph77.4 mph+2.4 mph
80 mph82.6 mph+2.6 mph

Each size on its own

Questions

Which is bigger, 265/25R20 or 255/30R20?
255/30R20 is taller by 0.81 inches (26.02" vs 25.22"). 265/25R20 is wider by 0.39 inches.
Can I replace 265/25R20 with 255/30R20?
It is not recommended without checking carefully. The diameter difference is +3.2%, 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 255/30R20 change my speedometer?
When your speedometer reads 60 mph with 255/30R20 fitted (calibrated for 265/25R20), your real speed is 61.9 mph. Your odometer will under-count miles by about 3.2%.
Will 255/30R20 lift my vehicle?
Ride height changes by half the diameter difference: +0.40 inches of ground clearance at the axle.

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