Tire Size Box

255/25R24 vs 255/30R24

255/30R24 compared with 255/25R24

+3.5% diameter, 0.0" width

255/30R24 is 30.02" tall vs 29.02". More than the 3% rule of thumb, so check carefully before switching.

29.0"24" rim2.5"10.0" wide
255/25R24 (solid) compared with 255/30R24 (dashed outline), drawn to scale

With 255/30R24 tires, when your speedometer says 60 mph you are really going

62.1 mph

255/30R24 is +1.00 inches (+3.5%) in overall diameter. That is more than the 3% most shops and makers recommend.

255/25R24255/30R24Difference%
Overall diameter29.02"30.02"+1.00"+3.5%
Section width10.04"10.04"0.00"0.0%
Sidewall height2.51"3.01"+0.50"+20.0%
Circumference91.17"94.32"+3.15"+3.5%
Revolutions per mile695.0671.7−23.2−3.3%

Speedometer difference

If your vehicle came with 255/25R24 and you fit 255/30R24, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.7 mph+0.7 mph
30 mph31.0 mph+1.0 mph
40 mph41.4 mph+1.4 mph
50 mph51.7 mph+1.7 mph
60 mph62.1 mph+2.1 mph
65 mph67.2 mph+2.2 mph
70 mph72.4 mph+2.4 mph
75 mph77.6 mph+2.6 mph
80 mph82.8 mph+2.8 mph

Each size on its own

Questions

Which is bigger, 255/25R24 or 255/30R24?
255/30R24 is taller by 1.00 inches (30.02" vs 29.02"). 255/25R24 is the same width.
Can I replace 255/25R24 with 255/30R24?
It is not recommended without checking carefully. The diameter difference is +3.5%, 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 255/30R24 change my speedometer?
When your speedometer reads 60 mph with 255/30R24 fitted (calibrated for 255/25R24), your real speed is 62.1 mph. Your odometer will under-count miles by about 3.5%.
Will 255/30R24 lift my vehicle?
Ride height changes by half the diameter difference: +0.50 inches of ground clearance at the axle.

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