Tire Size Box

305/55R20 vs 305/60R20

305/60R20 compared with 305/55R20

+3.6% diameter, 0.0" width

305/60R20 is 34.41" tall vs 33.21". More than the 3% rule of thumb, so check carefully before switching.

33.2"20" rim6.6"12.0" wide
305/55R20 (solid) compared with 305/60R20 (dashed outline), drawn to scale

With 305/60R20 tires, when your speedometer says 60 mph you are really going

62.2 mph

305/60R20 is +1.20 inches (+3.6%) in overall diameter. That is more than the 3% most shops and makers recommend.

305/55R20305/60R20Difference%
Overall diameter33.21"34.41"+1.20"+3.6%
Section width12.01"12.01"0.00"0.0%
Sidewall height6.60"7.20"+0.60"+9.1%
Circumference104.33"108.10"+3.77"+3.6%
Revolutions per mile607.3586.1−21.2−3.5%

Speedometer difference

If your vehicle came with 305/55R20 and you fit 305/60R20, 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 mph41.4 mph+1.4 mph
50 mph51.8 mph+1.8 mph
60 mph62.2 mph+2.2 mph
65 mph67.4 mph+2.4 mph
70 mph72.5 mph+2.5 mph
75 mph77.7 mph+2.7 mph
80 mph82.9 mph+2.9 mph

Each size on its own

Questions

Which is bigger, 305/55R20 or 305/60R20?
305/60R20 is taller by 1.20 inches (34.41" vs 33.21"). 305/55R20 is the same width.
Can I replace 305/55R20 with 305/60R20?
It is not recommended without checking carefully. The diameter difference is +3.6%, 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 305/60R20 change my speedometer?
When your speedometer reads 60 mph with 305/60R20 fitted (calibrated for 305/55R20), your real speed is 62.2 mph. Your odometer will under-count miles by about 3.6%.
Will 305/60R20 lift my vehicle?
Ride height changes by half the diameter difference: +0.60 inches of ground clearance at the axle.

Other comparisons