Tire Size Box

305/60R20 vs 305/65R20

305/65R20 compared with 305/60R20

+3.5% diameter, 0.0" width

305/65R20 is 35.61" tall vs 34.41". More than the 3% rule of thumb, so check carefully before switching.

34.4"20" rim7.2"12.0" wide
305/60R20 (solid) compared with 305/65R20 (dashed outline), drawn to scale

With 305/65R20 tires, when your speedometer says 60 mph you are really going

62.1 mph

305/65R20 is +1.20 inches (+3.5%) in overall diameter. That is more than the 3% most shops and makers recommend.

305/60R20305/65R20Difference%
Overall diameter34.41"35.61"+1.20"+3.5%
Section width12.01"12.01"0.00"0.0%
Sidewall height7.20"7.81"+0.60"+8.3%
Circumference108.10"111.87"+3.77"+3.5%
Revolutions per mile586.1566.4−19.8−3.4%

Speedometer difference

If your vehicle came with 305/60R20 and you fit 305/65R20, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.7 mph+0.7 mph
30 mph31.0 mph+1.0 mph
40 mph41.4 mph+1.4 mph
50 mph51.7 mph+1.7 mph
60 mph62.1 mph+2.1 mph
65 mph67.3 mph+2.3 mph
70 mph72.4 mph+2.4 mph
75 mph77.6 mph+2.6 mph
80 mph82.8 mph+2.8 mph

Each size on its own

Questions

Which is bigger, 305/60R20 or 305/65R20?
305/65R20 is taller by 1.20 inches (35.61" vs 34.41"). 305/60R20 is the same width.
Can I replace 305/60R20 with 305/65R20?
It is not recommended without checking carefully. The diameter difference is +3.5%, 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 305/65R20 change my speedometer?
When your speedometer reads 60 mph with 305/65R20 fitted (calibrated for 305/60R20), your real speed is 62.1 mph. Your odometer will under-count miles by about 3.5%.
Will 305/65R20 lift my vehicle?
Ride height changes by half the diameter difference: +0.60 inches of ground clearance at the axle.

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