Tire Size Box

265/40R21 vs 265/50R21

265/50R21 compared with 265/40R21

+7.1% diameter, 0.0" width

265/50R21 is 31.43" tall vs 29.35". More than the 3% rule of thumb, so check carefully before switching.

29.3"21" rim4.2"10.4" wide
265/40R21 (solid) compared with 265/50R21 (dashed outline), drawn to scale

With 265/50R21 tires, when your speedometer says 60 mph you are really going

64.3 mph

265/50R21 is +2.09 inches (+7.1%) in overall diameter. That is more than the 3% most shops and makers recommend.

265/40R21265/50R21Difference%
Overall diameter29.35"31.43"+2.09"+7.1%
Section width10.43"10.43"0.00"0.0%
Sidewall height4.17"5.22"+1.04"+25.0%
Circumference92.19"98.75"+6.56"+7.1%
Revolutions per mile687.2641.6−45.6−6.6%

Speedometer difference

If your vehicle came with 265/40R21 and you fit 265/50R21, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.4 mph+1.4 mph
30 mph32.1 mph+2.1 mph
40 mph42.8 mph+2.8 mph
50 mph53.6 mph+3.6 mph
60 mph64.3 mph+4.3 mph
65 mph69.6 mph+4.6 mph
70 mph75.0 mph+5.0 mph
75 mph80.3 mph+5.3 mph
80 mph85.7 mph+5.7 mph

Each size on its own

Questions

Which is bigger, 265/40R21 or 265/50R21?
265/50R21 is taller by 2.09 inches (31.43" vs 29.35"). 265/40R21 is the same width.
Can I replace 265/40R21 with 265/50R21?
It is not recommended without checking carefully. The diameter difference is +7.1%, 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 265/50R21 change my speedometer?
When your speedometer reads 60 mph with 265/50R21 fitted (calibrated for 265/40R21), your real speed is 64.3 mph. Your odometer will under-count miles by about 7.1%.
Will 265/50R21 lift my vehicle?
Ride height changes by half the diameter difference: +1.04 inches of ground clearance at the axle.

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