Tire Size Box

275/40R20 vs 275/50R20

275/50R20 compared with 275/40R20

+7.6% diameter, 0.0" width

275/50R20 is 30.83" tall vs 28.66". More than the 3% rule of thumb, so check carefully before switching.

28.7"20" rim4.3"10.8" wide
275/40R20 (solid) compared with 275/50R20 (dashed outline), drawn to scale

With 275/50R20 tires, when your speedometer says 60 mph you are really going

64.5 mph

275/50R20 is +2.17 inches (+7.6%) in overall diameter. That is more than the 3% most shops and makers recommend.

275/40R20275/50R20Difference%
Overall diameter28.66"30.83"+2.17"+7.6%
Section width10.83"10.83"0.00"0.0%
Sidewall height4.33"5.41"+1.08"+25.0%
Circumference90.04"96.85"+6.80"+7.6%
Revolutions per mile703.7654.2−49.4−7.0%

Speedometer difference

If your vehicle came with 275/40R20 and you fit 275/50R20, 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 mph80.7 mph+5.7 mph
80 mph86.0 mph+6.0 mph

Each size on its own

Questions

Which is bigger, 275/40R20 or 275/50R20?
275/50R20 is taller by 2.17 inches (30.83" vs 28.66"). 275/40R20 is the same width.
Can I replace 275/40R20 with 275/50R20?
It is not recommended without checking carefully. The diameter difference is +7.6%, 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 275/50R20 change my speedometer?
When your speedometer reads 60 mph with 275/50R20 fitted (calibrated for 275/40R20), your real speed is 64.5 mph. Your odometer will under-count miles by about 7.6%.
Will 275/50R20 lift my vehicle?
Ride height changes by half the diameter difference: +1.08 inches of ground clearance at the axle.

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