Tire Size Box

265/40R20 vs 265/50R20

265/50R20 compared with 265/40R20

+7.4% diameter, 0.0" width

265/50R20 is 30.43" tall vs 28.35". More than the 3% rule of thumb, so check carefully before switching.

28.3"20" rim4.2"10.4" wide
265/40R20 (solid) compared with 265/50R20 (dashed outline), drawn to scale

With 265/50R20 tires, when your speedometer says 60 mph you are really going

64.4 mph

265/50R20 is +2.09 inches (+7.4%) in overall diameter. That is more than the 3% most shops and makers recommend.

265/40R20265/50R20Difference%
Overall diameter28.35"30.43"+2.09"+7.4%
Section width10.43"10.43"0.00"0.0%
Sidewall height4.17"5.22"+1.04"+25.0%
Circumference89.05"95.61"+6.56"+7.4%
Revolutions per mile711.5662.7−48.8−6.9%

Speedometer difference

If your vehicle came with 265/40R20 and you fit 265/50R20, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.5 mph+1.5 mph
30 mph32.2 mph+2.2 mph
40 mph42.9 mph+2.9 mph
50 mph53.7 mph+3.7 mph
60 mph64.4 mph+4.4 mph
65 mph69.8 mph+4.8 mph
70 mph75.2 mph+5.2 mph
75 mph80.5 mph+5.5 mph
80 mph85.9 mph+5.9 mph

Each size on its own

Questions

Which is bigger, 265/40R20 or 265/50R20?
265/50R20 is taller by 2.09 inches (30.43" vs 28.35"). 265/40R20 is the same width.
Can I replace 265/40R20 with 265/50R20?
It is not recommended without checking carefully. The diameter difference is +7.4%, 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 265/50R20 change my speedometer?
When your speedometer reads 60 mph with 265/50R20 fitted (calibrated for 265/40R20), your real speed is 64.4 mph. Your odometer will under-count miles by about 7.4%.
Will 265/50R20 lift my vehicle?
Ride height changes by half the diameter difference: +1.04 inches of ground clearance at the axle.

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