Tire Size Box

245/55R20 vs 245/65R20

245/65R20 compared with 245/55R20

+6.3% diameter, 0.0" width

245/65R20 is 32.54" tall vs 30.61". More than the 3% rule of thumb, so check carefully before switching.

30.6"20" rim5.3"9.6" wide
245/55R20 (solid) compared with 245/65R20 (dashed outline), drawn to scale

With 245/65R20 tires, when your speedometer says 60 mph you are really going

63.8 mph

245/65R20 is +1.93 inches (+6.3%) in overall diameter. That is more than the 3% most shops and makers recommend.

245/55R20245/65R20Difference%
Overall diameter30.61"32.54"+1.93"+6.3%
Section width9.65"9.65"0.00"0.0%
Sidewall height5.31"6.27"+0.96"+18.2%
Circumference96.16"102.23"+6.06"+6.3%
Revolutions per mile658.9619.8−39.1−5.9%

Speedometer difference

If your vehicle came with 245/55R20 and you fit 245/65R20, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.3 mph+1.3 mph
30 mph31.9 mph+1.9 mph
40 mph42.5 mph+2.5 mph
50 mph53.2 mph+3.2 mph
60 mph63.8 mph+3.8 mph
65 mph69.1 mph+4.1 mph
70 mph74.4 mph+4.4 mph
75 mph79.7 mph+4.7 mph
80 mph85.0 mph+5.0 mph

Each size on its own

Questions

Which is bigger, 245/55R20 or 245/65R20?
245/65R20 is taller by 1.93 inches (32.54" vs 30.61"). 245/55R20 is the same width.
Can I replace 245/55R20 with 245/65R20?
It is not recommended without checking carefully. The diameter difference is +6.3%, 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 245/65R20 change my speedometer?
When your speedometer reads 60 mph with 245/65R20 fitted (calibrated for 245/55R20), your real speed is 63.8 mph. Your odometer will under-count miles by about 6.3%.
Will 245/65R20 lift my vehicle?
Ride height changes by half the diameter difference: +0.96 inches of ground clearance at the axle.

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