Tire Size Box

225/55R18 vs 225/65R18

225/65R18 compared with 225/55R18

+6.4% diameter, 0.0" width

225/65R18 is 29.52" tall vs 27.74". More than the 3% rule of thumb, so check carefully before switching.

27.7"18" rim4.9"8.9" wide
225/55R18 (solid) compared with 225/65R18 (dashed outline), drawn to scale

With 225/65R18 tires, when your speedometer says 60 mph you are really going

63.8 mph

225/65R18 is +1.77 inches (+6.4%) in overall diameter. That is more than the 3% most shops and makers recommend.

225/55R18225/65R18Difference%
Overall diameter27.74"29.52"+1.77"+6.4%
Section width8.86"8.86"0.00"0.0%
Sidewall height4.87"5.76"+0.89"+18.2%
Circumference87.16"92.73"+5.57"+6.4%
Revolutions per mile726.9683.3−43.6−6.0%

Speedometer difference

If your vehicle came with 225/55R18 and you fit 225/65R18, 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 mph42.6 mph+2.6 mph
50 mph53.2 mph+3.2 mph
60 mph63.8 mph+3.8 mph
65 mph69.2 mph+4.2 mph
70 mph74.5 mph+4.5 mph
75 mph79.8 mph+4.8 mph
80 mph85.1 mph+5.1 mph

Each size on its own

Questions

Which is bigger, 225/55R18 or 225/65R18?
225/65R18 is taller by 1.77 inches (29.52" vs 27.74"). 225/55R18 is the same width.
Can I replace 225/55R18 with 225/65R18?
It is not recommended without checking carefully. The diameter difference is +6.4%, 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 225/65R18 change my speedometer?
When your speedometer reads 60 mph with 225/65R18 fitted (calibrated for 225/55R18), your real speed is 63.8 mph. Your odometer will under-count miles by about 6.4%.
Will 225/65R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.89 inches of ground clearance at the axle.

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