Tire Size Box

305/60R18 vs 305/65R18

305/65R18 compared with 305/60R18

+3.7% diameter, 0.0" width

305/65R18 is 33.61" tall vs 32.41". More than the 3% rule of thumb, so check carefully before switching.

32.4"18" rim7.2"12.0" wide
305/60R18 (solid) compared with 305/65R18 (dashed outline), drawn to scale

With 305/65R18 tires, when your speedometer says 60 mph you are really going

62.2 mph

305/65R18 is +1.20 inches (+3.7%) in overall diameter. That is more than the 3% most shops and makers recommend.

305/60R18305/65R18Difference%
Overall diameter32.41"33.61"+1.20"+3.7%
Section width12.01"12.01"0.00"0.0%
Sidewall height7.20"7.81"+0.60"+8.3%
Circumference101.82"105.59"+3.77"+3.7%
Revolutions per mile622.3600.1−22.2−3.6%

Speedometer difference

If your vehicle came with 305/60R18 and you fit 305/65R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.7 mph+0.7 mph
30 mph31.1 mph+1.1 mph
40 mph41.5 mph+1.5 mph
50 mph51.9 mph+1.9 mph
60 mph62.2 mph+2.2 mph
65 mph67.4 mph+2.4 mph
70 mph72.6 mph+2.6 mph
75 mph77.8 mph+2.8 mph
80 mph83.0 mph+3.0 mph

Each size on its own

Questions

Which is bigger, 305/60R18 or 305/65R18?
305/65R18 is taller by 1.20 inches (33.61" vs 32.41"). 305/60R18 is the same width.
Can I replace 305/60R18 with 305/65R18?
It is not recommended without checking carefully. The diameter difference is +3.7%, 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 305/65R18 change my speedometer?
When your speedometer reads 60 mph with 305/65R18 fitted (calibrated for 305/60R18), your real speed is 62.2 mph. Your odometer will under-count miles by about 3.7%.
Will 305/65R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.60 inches of ground clearance at the axle.

Other comparisons