Tire Size Box

245/55R18 vs 245/65R18

245/65R18 compared with 245/55R18

+6.7% diameter, 0.0" width

245/65R18 is 30.54" tall vs 28.61". More than the 3% rule of thumb, so check carefully before switching.

28.6"18" rim5.3"9.6" wide
245/55R18 (solid) compared with 245/65R18 (dashed outline), drawn to scale

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

64.0 mph

245/65R18 is +1.93 inches (+6.7%) in overall diameter. That is more than the 3% most shops and makers recommend.

245/55R18245/65R18Difference%
Overall diameter28.61"30.54"+1.93"+6.7%
Section width9.65"9.65"0.00"0.0%
Sidewall height5.31"6.27"+0.96"+18.2%
Circumference89.88"95.94"+6.06"+6.7%
Revolutions per mile704.9660.4−44.5−6.3%

Speedometer difference

If your vehicle came with 245/55R18 and you fit 245/65R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.3 mph+1.3 mph
30 mph32.0 mph+2.0 mph
40 mph42.7 mph+2.7 mph
50 mph53.4 mph+3.4 mph
60 mph64.0 mph+4.0 mph
65 mph69.4 mph+4.4 mph
70 mph74.7 mph+4.7 mph
75 mph80.1 mph+5.1 mph
80 mph85.4 mph+5.4 mph

Each size on its own

Questions

Which is bigger, 245/55R18 or 245/65R18?
245/65R18 is taller by 1.93 inches (30.54" vs 28.61"). 245/55R18 is the same width.
Can I replace 245/55R18 with 245/65R18?
It is not recommended without checking carefully. The diameter difference is +6.7%, 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 245/55R18), your real speed is 64.0 mph. Your odometer will under-count miles by about 6.7%.
Will 245/65R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.96 inches of ground clearance at the axle.

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