Tire Size Box

225/70R18 vs 245/70R18

245/70R18 compared with 225/70R18

+3.6% diameter, +0.8" width

245/70R18 is 31.50" tall vs 30.40". More than the 3% rule of thumb, so check carefully before switching.

30.4"18" rim6.2"8.9" wide
225/70R18 (solid) compared with 245/70R18 (dashed outline), drawn to scale

With 245/70R18 tires, when your speedometer says 60 mph you are really going

62.2 mph

245/70R18 is +1.10 inches (+3.6%) in overall diameter. That is more than the 3% most shops and makers recommend.

225/70R18245/70R18Difference%
Overall diameter30.40"31.50"+1.10"+3.6%
Section width8.86"9.65"+0.79"+8.9%
Sidewall height6.20"6.75"+0.55"+8.9%
Circumference95.51"98.97"+3.46"+3.6%
Revolutions per mile663.4640.2−23.2−3.5%

Speedometer difference

If your vehicle came with 225/70R18 and you fit 245/70R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.7 mph+0.7 mph
30 mph31.1 mph+1.1 mph
40 mph41.5 mph+1.5 mph
50 mph51.8 mph+1.8 mph
60 mph62.2 mph+2.2 mph
65 mph67.4 mph+2.4 mph
70 mph72.5 mph+2.5 mph
75 mph77.7 mph+2.7 mph
80 mph82.9 mph+2.9 mph

Each size on its own

Questions

Which is bigger, 225/70R18 or 245/70R18?
245/70R18 is taller by 1.10 inches (31.50" vs 30.40"). 245/70R18 is wider by 0.79 inches.
Can I replace 225/70R18 with 245/70R18?
It is not recommended without checking carefully. The diameter difference is +3.6%, 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 245/70R18 change my speedometer?
When your speedometer reads 60 mph with 245/70R18 fitted (calibrated for 225/70R18), your real speed is 62.2 mph. Your odometer will under-count miles by about 3.6%.
Will 245/70R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.55 inches of ground clearance at the axle.

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