Tire Size Box

235/55R20 vs 235/65R20

235/65R20 compared with 235/55R20

+6.1% diameter, 0.0" width

235/65R20 is 32.03" tall vs 30.18". More than the 3% rule of thumb, so check carefully before switching.

30.2"20" rim5.1"9.3" wide
235/55R20 (solid) compared with 235/65R20 (dashed outline), drawn to scale

With 235/65R20 tires, when your speedometer says 60 mph you are really going

63.7 mph

235/65R20 is +1.85 inches (+6.1%) in overall diameter. That is more than the 3% most shops and makers recommend.

235/55R20235/65R20Difference%
Overall diameter30.18"32.03"+1.85"+6.1%
Section width9.25"9.25"0.00"0.0%
Sidewall height5.09"6.01"+0.93"+18.2%
Circumference94.80"100.62"+5.81"+6.1%
Revolutions per mile668.3629.7−38.6−5.8%

Speedometer difference

If your vehicle came with 235/55R20 and you fit 235/65R20, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.2 mph+1.2 mph
30 mph31.8 mph+1.8 mph
40 mph42.5 mph+2.5 mph
50 mph53.1 mph+3.1 mph
60 mph63.7 mph+3.7 mph
65 mph69.0 mph+4.0 mph
70 mph74.3 mph+4.3 mph
75 mph79.6 mph+4.6 mph
80 mph84.9 mph+4.9 mph

Each size on its own

Questions

Which is bigger, 235/55R20 or 235/65R20?
235/65R20 is taller by 1.85 inches (32.03" vs 30.18"). 235/55R20 is the same width.
Can I replace 235/55R20 with 235/65R20?
It is not recommended without checking carefully. The diameter difference is +6.1%, 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 235/65R20 change my speedometer?
When your speedometer reads 60 mph with 235/65R20 fitted (calibrated for 235/55R20), your real speed is 63.7 mph. Your odometer will under-count miles by about 6.1%.
Will 235/65R20 lift my vehicle?
Ride height changes by half the diameter difference: +0.93 inches of ground clearance at the axle.

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