Tire Size Box

225/40R21 vs 225/50R21

225/50R21 compared with 225/40R21

+6.3% diameter, 0.0" width

225/50R21 is 29.86" tall vs 28.09". More than the 3% rule of thumb, so check carefully before switching.

28.1"21" rim3.5"8.9" wide
225/40R21 (solid) compared with 225/50R21 (dashed outline), drawn to scale

With 225/50R21 tires, when your speedometer says 60 mph you are really going

63.8 mph

225/50R21 is +1.77 inches (+6.3%) in overall diameter. That is more than the 3% most shops and makers recommend.

225/40R21225/50R21Difference%
Overall diameter28.09"29.86"+1.77"+6.3%
Section width8.86"8.86"0.00"0.0%
Sidewall height3.54"4.43"+0.89"+25.0%
Circumference88.24"93.80"+5.57"+6.3%
Revolutions per mile718.1675.5−42.6−5.9%

Speedometer difference

If your vehicle came with 225/40R21 and you fit 225/50R21, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.3 mph+1.3 mph
30 mph31.9 mph+1.9 mph
40 mph42.5 mph+2.5 mph
50 mph53.2 mph+3.2 mph
60 mph63.8 mph+3.8 mph
65 mph69.1 mph+4.1 mph
70 mph74.4 mph+4.4 mph
75 mph79.7 mph+4.7 mph
80 mph85.0 mph+5.0 mph

Each size on its own

Questions

Which is bigger, 225/40R21 or 225/50R21?
225/50R21 is taller by 1.77 inches (29.86" vs 28.09"). 225/40R21 is the same width.
Can I replace 225/40R21 with 225/50R21?
It is not recommended without checking carefully. The diameter difference is +6.3%, 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 225/50R21 change my speedometer?
When your speedometer reads 60 mph with 225/50R21 fitted (calibrated for 225/40R21), your real speed is 63.8 mph. Your odometer will under-count miles by about 6.3%.
Will 225/50R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.89 inches of ground clearance at the axle.

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