Tire Size Box

245/65R18 vs 245/75R18

245/75R18 compared with 245/65R18

+6.3% diameter, 0.0" width

245/75R18 is 32.47" tall vs 30.54". More than the 3% rule of thumb, so check carefully before switching.

30.5"18" rim6.3"9.6" wide
245/65R18 (solid) compared with 245/75R18 (dashed outline), drawn to scale

With 245/75R18 tires, when your speedometer says 60 mph you are really going

63.8 mph

245/75R18 is +1.93 inches (+6.3%) in overall diameter. That is more than the 3% most shops and makers recommend.

245/65R18245/75R18Difference%
Overall diameter30.54"32.47"+1.93"+6.3%
Section width9.65"9.65"0.00"0.0%
Sidewall height6.27"7.23"+0.96"+15.4%
Circumference95.94"102.00"+6.06"+6.3%
Revolutions per mile660.4621.2−39.2−5.9%

Speedometer difference

If your vehicle came with 245/65R18 and you fit 245/75R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.3 mph+1.3 mph
30 mph31.9 mph+1.9 mph
40 mph42.5 mph+2.5 mph
50 mph53.2 mph+3.2 mph
60 mph63.8 mph+3.8 mph
65 mph69.1 mph+4.1 mph
70 mph74.4 mph+4.4 mph
75 mph79.7 mph+4.7 mph
80 mph85.1 mph+5.1 mph

Each size on its own

Questions

Which is bigger, 245/65R18 or 245/75R18?
245/75R18 is taller by 1.93 inches (32.47" vs 30.54"). 245/65R18 is the same width.
Can I replace 245/65R18 with 245/75R18?
It is not recommended without checking carefully. The diameter difference is +6.3%, 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 245/75R18 change my speedometer?
When your speedometer reads 60 mph with 245/75R18 fitted (calibrated for 245/65R18), your real speed is 63.8 mph. Your odometer will under-count miles by about 6.3%.
Will 245/75R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.96 inches of ground clearance at the axle.

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