Tire Size Box

205/55R18 vs 205/65R18

205/65R18 compared with 205/55R18

+6.0% diameter, 0.0" width

205/65R18 is 28.49" tall vs 26.88". More than the 3% rule of thumb, so check carefully before switching.

26.9"18" rim4.4"8.1" wide
205/55R18 (solid) compared with 205/65R18 (dashed outline), drawn to scale

With 205/65R18 tires, when your speedometer says 60 mph you are really going

63.6 mph

205/65R18 is +1.61 inches (+6.0%) in overall diameter. That is more than the 3% most shops and makers recommend.

205/55R18205/65R18Difference%
Overall diameter26.88"28.49"+1.61"+6.0%
Section width8.07"8.07"0.00"0.0%
Sidewall height4.44"5.25"+0.81"+18.2%
Circumference84.44"89.51"+5.07"+6.0%
Revolutions per mile750.4707.8−42.5−5.7%

Speedometer difference

If your vehicle came with 205/55R18 and you fit 205/65R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.2 mph+1.2 mph
30 mph31.8 mph+1.8 mph
40 mph42.4 mph+2.4 mph
50 mph53.0 mph+3.0 mph
60 mph63.6 mph+3.6 mph
65 mph68.9 mph+3.9 mph
70 mph74.2 mph+4.2 mph
75 mph79.5 mph+4.5 mph
80 mph84.8 mph+4.8 mph

Each size on its own

Questions

Which is bigger, 205/55R18 or 205/65R18?
205/65R18 is taller by 1.61 inches (28.49" vs 26.88"). 205/55R18 is the same width.
Can I replace 205/55R18 with 205/65R18?
It is not recommended without checking carefully. The diameter difference is +6.0%, 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 205/65R18 change my speedometer?
When your speedometer reads 60 mph with 205/65R18 fitted (calibrated for 205/55R18), your real speed is 63.6 mph. Your odometer will under-count miles by about 6.0%.
Will 205/65R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.81 inches of ground clearance at the axle.

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