Tire Size Box

235/45R20 vs 235/50R20

235/50R20 compared with 235/45R20

+3.3% diameter, 0.0" width

235/50R20 is 29.25" tall vs 28.33". More than the 3% rule of thumb, so check carefully before switching.

28.3"20" rim4.2"9.3" wide
235/45R20 (solid) compared with 235/50R20 (dashed outline), drawn to scale

With 235/50R20 tires, when your speedometer says 60 mph you are really going

62.0 mph

235/50R20 is +0.93 inches (+3.3%) in overall diameter. That is more than the 3% most shops and makers recommend.

235/45R20235/50R20Difference%
Overall diameter28.33"29.25"+0.93"+3.3%
Section width9.25"9.25"0.00"0.0%
Sidewall height4.16"4.63"+0.46"+11.1%
Circumference88.99"91.90"+2.91"+3.3%
Revolutions per mile712.0689.5−22.5−3.2%

Speedometer difference

If your vehicle came with 235/45R20 and you fit 235/50R20, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.7 mph+0.7 mph
30 mph31.0 mph+1.0 mph
40 mph41.3 mph+1.3 mph
50 mph51.6 mph+1.6 mph
60 mph62.0 mph+2.0 mph
65 mph67.1 mph+2.1 mph
70 mph72.3 mph+2.3 mph
75 mph77.4 mph+2.4 mph
80 mph82.6 mph+2.6 mph

Each size on its own

Questions

Which is bigger, 235/45R20 or 235/50R20?
235/50R20 is taller by 0.93 inches (29.25" vs 28.33"). 235/45R20 is the same width.
Can I replace 235/45R20 with 235/50R20?
It is not recommended without checking carefully. The diameter difference is +3.3%, 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 235/50R20 change my speedometer?
When your speedometer reads 60 mph with 235/50R20 fitted (calibrated for 235/45R20), your real speed is 62.0 mph. Your odometer will under-count miles by about 3.3%.
Will 235/50R20 lift my vehicle?
Ride height changes by half the diameter difference: +0.46 inches of ground clearance at the axle.

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