Tire Size Box

305/55R18 vs 305/60R18

305/60R18 compared with 305/55R18

+3.8% diameter, 0.0" width

305/60R18 is 32.41" tall vs 31.21". More than the 3% rule of thumb, so check carefully before switching.

31.2"18" rim6.6"12.0" wide
305/55R18 (solid) compared with 305/60R18 (dashed outline), drawn to scale

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

62.3 mph

305/60R18 is +1.20 inches (+3.8%) in overall diameter. That is more than the 3% most shops and makers recommend.

305/55R18305/60R18Difference%
Overall diameter31.21"32.41"+1.20"+3.8%
Section width12.01"12.01"0.00"0.0%
Sidewall height6.60"7.20"+0.60"+9.1%
Circumference98.04"101.82"+3.77"+3.8%
Revolutions per mile646.2622.3−23.9−3.7%

Speedometer difference

If your vehicle came with 305/55R18 and you fit 305/60R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.8 mph+0.8 mph
30 mph31.2 mph+1.2 mph
40 mph41.5 mph+1.5 mph
50 mph51.9 mph+1.9 mph
60 mph62.3 mph+2.3 mph
65 mph67.5 mph+2.5 mph
70 mph72.7 mph+2.7 mph
75 mph77.9 mph+2.9 mph
80 mph83.1 mph+3.1 mph

Each size on its own

Questions

Which is bigger, 305/55R18 or 305/60R18?
305/60R18 is taller by 1.20 inches (32.41" vs 31.21"). 305/55R18 is the same width.
Can I replace 305/55R18 with 305/60R18?
It is not recommended without checking carefully. The diameter difference is +3.8%, 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 305/60R18 change my speedometer?
When your speedometer reads 60 mph with 305/60R18 fitted (calibrated for 305/55R18), your real speed is 62.3 mph. Your odometer will under-count miles by about 3.8%.
Will 305/60R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.60 inches of ground clearance at the axle.

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