Tire Size Box

245/40R21 vs 245/50R21

245/50R21 compared with 245/40R21

+6.7% diameter, 0.0" width

245/50R21 is 30.65" tall vs 28.72". More than the 3% rule of thumb, so check carefully before switching.

28.7"21" rim3.9"9.6" wide
245/40R21 (solid) compared with 245/50R21 (dashed outline), drawn to scale

With 245/50R21 tires, when your speedometer says 60 mph you are really going

64.0 mph

245/50R21 is +1.93 inches (+6.7%) in overall diameter. That is more than the 3% most shops and makers recommend.

245/40R21245/50R21Difference%
Overall diameter28.72"30.65"+1.93"+6.7%
Section width9.65"9.65"0.00"0.0%
Sidewall height3.86"4.82"+0.96"+25.0%
Circumference90.22"96.28"+6.06"+6.7%
Revolutions per mile702.3658.1−44.2−6.3%

Speedometer difference

If your vehicle came with 245/40R21 and you fit 245/50R21, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.3 mph+1.3 mph
30 mph32.0 mph+2.0 mph
40 mph42.7 mph+2.7 mph
50 mph53.4 mph+3.4 mph
60 mph64.0 mph+4.0 mph
65 mph69.4 mph+4.4 mph
70 mph74.7 mph+4.7 mph
75 mph80.0 mph+5.0 mph
80 mph85.4 mph+5.4 mph

Each size on its own

Questions

Which is bigger, 245/40R21 or 245/50R21?
245/50R21 is taller by 1.93 inches (30.65" vs 28.72"). 245/40R21 is the same width.
Can I replace 245/40R21 with 245/50R21?
It is not recommended without checking carefully. The diameter difference is +6.7%, 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 245/50R21 change my speedometer?
When your speedometer reads 60 mph with 245/50R21 fitted (calibrated for 245/40R21), your real speed is 64.0 mph. Your odometer will under-count miles by about 6.7%.
Will 245/50R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.96 inches of ground clearance at the axle.

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