Tire Size Box

275/40R21 vs 275/50R21

275/50R21 compared with 275/40R21

+7.3% diameter, 0.0" width

275/50R21 is 31.83" tall vs 29.66". More than the 3% rule of thumb, so check carefully before switching.

29.7"21" rim4.3"10.8" wide
275/40R21 (solid) compared with 275/50R21 (dashed outline), drawn to scale

With 275/50R21 tires, when your speedometer says 60 mph you are really going

64.4 mph

275/50R21 is +2.17 inches (+7.3%) in overall diameter. That is more than the 3% most shops and makers recommend.

275/40R21275/50R21Difference%
Overall diameter29.66"31.83"+2.17"+7.3%
Section width10.83"10.83"0.00"0.0%
Sidewall height4.33"5.41"+1.08"+25.0%
Circumference93.18"99.99"+6.80"+7.3%
Revolutions per mile679.9633.7−46.3−6.8%

Speedometer difference

If your vehicle came with 275/40R21 and you fit 275/50R21, 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 mph69.7 mph+4.7 mph
70 mph75.1 mph+5.1 mph
75 mph80.5 mph+5.5 mph
80 mph85.8 mph+5.8 mph

Each size on its own

Questions

Which is bigger, 275/40R21 or 275/50R21?
275/50R21 is taller by 2.17 inches (31.83" vs 29.66"). 275/40R21 is the same width.
Can I replace 275/40R21 with 275/50R21?
It is not recommended without checking carefully. The diameter difference is +7.3%, 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 275/50R21 change my speedometer?
When your speedometer reads 60 mph with 275/50R21 fitted (calibrated for 275/40R21), your real speed is 64.4 mph. Your odometer will under-count miles by about 7.3%.
Will 275/50R21 lift my vehicle?
Ride height changes by half the diameter difference: +1.08 inches of ground clearance at the axle.

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