Tire Size Box

265/55R18 vs 265/65R18

265/65R18 compared with 265/55R18

+7.1% diameter, 0.0" width

265/65R18 is 31.56" tall vs 29.48". More than the 3% rule of thumb, so check carefully before switching.

29.5"18" rim5.7"10.4" wide
265/55R18 (solid) compared with 265/65R18 (dashed outline), drawn to scale

With 265/65R18 tires, when your speedometer says 60 mph you are really going

64.2 mph

265/65R18 is +2.09 inches (+7.1%) in overall diameter. That is more than the 3% most shops and makers recommend.

265/55R18265/65R18Difference%
Overall diameter29.48"31.56"+2.09"+7.1%
Section width10.43"10.43"0.00"0.0%
Sidewall height5.74"6.78"+1.04"+18.2%
Circumference92.60"99.16"+6.56"+7.1%
Revolutions per mile684.2639.0−45.2−6.6%

Speedometer difference

If your vehicle came with 265/55R18 and you fit 265/65R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.4 mph+1.4 mph
30 mph32.1 mph+2.1 mph
40 mph42.8 mph+2.8 mph
50 mph53.5 mph+3.5 mph
60 mph64.2 mph+4.2 mph
65 mph69.6 mph+4.6 mph
70 mph75.0 mph+5.0 mph
75 mph80.3 mph+5.3 mph
80 mph85.7 mph+5.7 mph

Each size on its own

Questions

Which is bigger, 265/55R18 or 265/65R18?
265/65R18 is taller by 2.09 inches (31.56" vs 29.48"). 265/55R18 is the same width.
Can I replace 265/55R18 with 265/65R18?
It is not recommended without checking carefully. The diameter difference is +7.1%, 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 265/65R18 change my speedometer?
When your speedometer reads 60 mph with 265/65R18 fitted (calibrated for 265/55R18), your real speed is 64.2 mph. Your odometer will under-count miles by about 7.1%.
Will 265/65R18 lift my vehicle?
Ride height changes by half the diameter difference: +1.04 inches of ground clearance at the axle.

Other comparisons