Tire Size Box

225/65R18 vs 245/65R18

245/65R18 compared with 225/65R18

+3.5% diameter, +0.8" width

245/65R18 is 30.54" tall vs 29.52". More than the 3% rule of thumb, so check carefully before switching.

29.5"18" rim5.8"8.9" wide
225/65R18 (solid) compared with 245/65R18 (dashed outline), drawn to scale

With 245/65R18 tires, when your speedometer says 60 mph you are really going

62.1 mph

245/65R18 is +1.02 inches (+3.5%) in overall diameter. That is more than the 3% most shops and makers recommend.

225/65R18245/65R18Difference%
Overall diameter29.52"30.54"+1.02"+3.5%
Section width8.86"9.65"+0.79"+8.9%
Sidewall height5.76"6.27"+0.51"+8.9%
Circumference92.73"95.94"+3.22"+3.5%
Revolutions per mile683.3660.4−22.9−3.4%

Speedometer difference

If your vehicle came with 225/65R18 and you fit 245/65R18, 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 mph67.3 mph+2.3 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, 225/65R18 or 245/65R18?
245/65R18 is taller by 1.02 inches (30.54" vs 29.52"). 245/65R18 is wider by 0.79 inches.
Can I replace 225/65R18 with 245/65R18?
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 245/65R18 change my speedometer?
When your speedometer reads 60 mph with 245/65R18 fitted (calibrated for 225/65R18), your real speed is 62.1 mph. Your odometer will under-count miles by about 3.5%.
Will 245/65R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.51 inches of ground clearance at the axle.

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