Tire Size Box

245/25R20 vs 245/30R20

245/30R20 compared with 245/25R20

+3.9% diameter, 0.0" width

245/30R20 is 25.79" tall vs 24.82". More than the 3% rule of thumb, so check carefully before switching.

24.8"20" rim2.4"9.6" wide
245/25R20 (solid) compared with 245/30R20 (dashed outline), drawn to scale

With 245/30R20 tires, when your speedometer says 60 mph you are really going

62.3 mph

245/30R20 is +0.96 inches (+3.9%) in overall diameter. That is more than the 3% most shops and makers recommend.

245/25R20245/30R20Difference%
Overall diameter24.82"25.79"+0.96"+3.9%
Section width9.65"9.65"0.00"0.0%
Sidewall height2.41"2.89"+0.48"+20.0%
Circumference77.98"81.01"+3.03"+3.9%
Revolutions per mile812.5782.1−30.4−3.7%

Speedometer difference

If your vehicle came with 245/25R20 and you fit 245/30R20, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.8 mph+0.8 mph
30 mph31.2 mph+1.2 mph
40 mph41.6 mph+1.6 mph
50 mph51.9 mph+1.9 mph
60 mph62.3 mph+2.3 mph
65 mph67.5 mph+2.5 mph
70 mph72.7 mph+2.7 mph
75 mph77.9 mph+2.9 mph
80 mph83.1 mph+3.1 mph

Each size on its own

Questions

Which is bigger, 245/25R20 or 245/30R20?
245/30R20 is taller by 0.96 inches (25.79" vs 24.82"). 245/25R20 is the same width.
Can I replace 245/25R20 with 245/30R20?
It is not recommended without checking carefully. The diameter difference is +3.9%, 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 245/30R20 change my speedometer?
When your speedometer reads 60 mph with 245/30R20 fitted (calibrated for 245/25R20), your real speed is 62.3 mph. Your odometer will under-count miles by about 3.9%.
Will 245/30R20 lift my vehicle?
Ride height changes by half the diameter difference: +0.48 inches of ground clearance at the axle.

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