Tire Size Box

275/55R20 vs 275/65R20

275/65R20 compared with 275/55R20

+6.8% diameter, 0.0" width

275/65R20 is 34.07" tall vs 31.91". More than the 3% rule of thumb, so check carefully before switching.

31.9"20" rim6.0"10.8" wide
275/55R20 (solid) compared with 275/65R20 (dashed outline), drawn to scale

With 275/65R20 tires, when your speedometer says 60 mph you are really going

64.1 mph

275/65R20 is +2.17 inches (+6.8%) in overall diameter. That is more than the 3% most shops and makers recommend.

275/55R20275/65R20Difference%
Overall diameter31.91"34.07"+2.17"+6.8%
Section width10.83"10.83"0.00"0.0%
Sidewall height5.95"7.04"+1.08"+18.2%
Circumference100.25"107.05"+6.80"+6.8%
Revolutions per mile632.0591.9−40.2−6.4%

Speedometer difference

If your vehicle came with 275/55R20 and you fit 275/65R20, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.4 mph+1.4 mph
30 mph32.0 mph+2.0 mph
40 mph42.7 mph+2.7 mph
50 mph53.4 mph+3.4 mph
60 mph64.1 mph+4.1 mph
65 mph69.4 mph+4.4 mph
70 mph74.8 mph+4.8 mph
75 mph80.1 mph+5.1 mph
80 mph85.4 mph+5.4 mph

Each size on its own

Questions

Which is bigger, 275/55R20 or 275/65R20?
275/65R20 is taller by 2.17 inches (34.07" vs 31.91"). 275/55R20 is the same width.
Can I replace 275/55R20 with 275/65R20?
It is not recommended without checking carefully. The diameter difference is +6.8%, 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 275/65R20 change my speedometer?
When your speedometer reads 60 mph with 275/65R20 fitted (calibrated for 275/55R20), your real speed is 64.1 mph. Your odometer will under-count miles by about 6.8%.
Will 275/65R20 lift my vehicle?
Ride height changes by half the diameter difference: +1.08 inches of ground clearance at the axle.

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