Tire Size Box

305/50R18 vs 305/60R18

305/60R18 compared with 305/50R18

+8.0% diameter, 0.0" width

305/60R18 is 32.41" tall vs 30.01". More than the 3% rule of thumb, so check carefully before switching.

30.0"18" rim6.0"12.0" wide
305/50R18 (solid) compared with 305/60R18 (dashed outline), drawn to scale

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

64.8 mph

305/60R18 is +2.40 inches (+8.0%) in overall diameter. That is more than the 3% most shops and makers recommend.

305/50R18305/60R18Difference%
Overall diameter30.01"32.41"+2.40"+8.0%
Section width12.01"12.01"0.00"0.0%
Sidewall height6.00"7.20"+1.20"+20.0%
Circumference94.27"101.82"+7.54"+8.0%
Revolutions per mile672.1622.3−49.8−7.4%

Speedometer difference

If your vehicle came with 305/50R18 and you fit 305/60R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.6 mph+1.6 mph
30 mph32.4 mph+2.4 mph
40 mph43.2 mph+3.2 mph
50 mph54.0 mph+4.0 mph
60 mph64.8 mph+4.8 mph
65 mph70.2 mph+5.2 mph
70 mph75.6 mph+5.6 mph
75 mph81.0 mph+6.0 mph
80 mph86.4 mph+6.4 mph

Each size on its own

Questions

Which is bigger, 305/50R18 or 305/60R18?
305/60R18 is taller by 2.40 inches (32.41" vs 30.01"). 305/50R18 is the same width.
Can I replace 305/50R18 with 305/60R18?
It is not recommended without checking carefully. The diameter difference is +8.0%, 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 305/60R18 change my speedometer?
When your speedometer reads 60 mph with 305/60R18 fitted (calibrated for 305/50R18), your real speed is 64.8 mph. Your odometer will under-count miles by about 8.0%.
Will 305/60R18 lift my vehicle?
Ride height changes by half the diameter difference: +1.20 inches of ground clearance at the axle.

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