Tire Size Box

235/45R21 vs 235/50R21

235/50R21 compared with 235/45R21

+3.2% diameter, 0.0" width

235/50R21 is 30.25" tall vs 29.33". More than the 3% rule of thumb, so check carefully before switching.

29.3"21" rim4.2"9.3" wide
235/45R21 (solid) compared with 235/50R21 (dashed outline), drawn to scale

With 235/50R21 tires, when your speedometer says 60 mph you are really going

61.9 mph

235/50R21 is +0.93 inches (+3.2%) in overall diameter. That is more than the 3% most shops and makers recommend.

235/45R21235/50R21Difference%
Overall diameter29.33"30.25"+0.93"+3.2%
Section width9.25"9.25"0.00"0.0%
Sidewall height4.16"4.63"+0.46"+11.1%
Circumference92.13"95.04"+2.91"+3.2%
Revolutions per mile687.7666.7−21.0−3.1%

Speedometer difference

If your vehicle came with 235/45R21 and you fit 235/50R21, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.6 mph+0.6 mph
30 mph30.9 mph+0.9 mph
40 mph41.3 mph+1.3 mph
50 mph51.6 mph+1.6 mph
60 mph61.9 mph+1.9 mph
65 mph67.1 mph+2.1 mph
70 mph72.2 mph+2.2 mph
75 mph77.4 mph+2.4 mph
80 mph82.5 mph+2.5 mph

Each size on its own

Questions

Which is bigger, 235/45R21 or 235/50R21?
235/50R21 is taller by 0.93 inches (30.25" vs 29.33"). 235/45R21 is the same width.
Can I replace 235/45R21 with 235/50R21?
It is not recommended without checking carefully. The diameter difference is +3.2%, 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 235/50R21 change my speedometer?
When your speedometer reads 60 mph with 235/50R21 fitted (calibrated for 235/45R21), your real speed is 61.9 mph. Your odometer will under-count miles by about 3.2%.
Will 235/50R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.46 inches of ground clearance at the axle.

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