Tire Size Box

305/50R20 vs 305/60R20

305/60R20 compared with 305/50R20

+7.5% diameter, 0.0" width

305/60R20 is 34.41" tall vs 32.01". More than the 3% rule of thumb, so check carefully before switching.

32.0"20" rim6.0"12.0" wide
305/50R20 (solid) compared with 305/60R20 (dashed outline), drawn to scale

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

64.5 mph

305/60R20 is +2.40 inches (+7.5%) in overall diameter. That is more than the 3% most shops and makers recommend.

305/50R20305/60R20Difference%
Overall diameter32.01"34.41"+2.40"+7.5%
Section width12.01"12.01"0.00"0.0%
Sidewall height6.00"7.20"+1.20"+20.0%
Circumference100.56"108.10"+7.54"+7.5%
Revolutions per mile630.1586.1−44.0−7.0%

Speedometer difference

If your vehicle came with 305/50R20 and you fit 305/60R20, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.5 mph+1.5 mph
30 mph32.3 mph+2.3 mph
40 mph43.0 mph+3.0 mph
50 mph53.8 mph+3.8 mph
60 mph64.5 mph+4.5 mph
65 mph69.9 mph+4.9 mph
70 mph75.3 mph+5.3 mph
75 mph80.6 mph+5.6 mph
80 mph86.0 mph+6.0 mph

Each size on its own

Questions

Which is bigger, 305/50R20 or 305/60R20?
305/60R20 is taller by 2.40 inches (34.41" vs 32.01"). 305/50R20 is the same width.
Can I replace 305/50R20 with 305/60R20?
It is not recommended without checking carefully. The diameter difference is +7.5%, 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 305/50R20), your real speed is 64.5 mph. Your odometer will under-count miles by about 7.5%.
Will 305/60R20 lift my vehicle?
Ride height changes by half the diameter difference: +1.20 inches of ground clearance at the axle.

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