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255/50R21 vs 275/55R20 tire size comparison

255/50R21275/55R20

275/55R20 is 0.9 in (2.80%) taller than 255/50R21 and 0.8 in wider. They fit different wheels: 255/50R21 a 21-inch wheel and 275/55R20 a 20-inch wheel.

255/50R21 and 275/55R20 side by side

+0.9 in / +2.80%255/50R21: 31.0 in tall, solid line275/55R20: 31.9 in tall, dashed line255/50R21Width 10.0 in (255 mm)Sidewall 5.0 in (128 mm)275/55R20Width 10.8 in (275 mm)Sidewall 6.0 in (151 mm)
255/50R21 is drawn with a solid line and 275/55R20 with a dashed line. In each drawing both tires are to the same scale; the tread shoulder and bead curves are simplified. The table below has the same numbers.
Dimensions of 255/50R21 and 275/55R20, with the difference (275/55R20 minus 255/50R21)
Measurement255/50R21275/55R20DifferenceDifference %
Section width10.0 in (255 mm)10.8 in (275 mm)+0.8 in (+20 mm)+7.84%
Sidewall height5.0 in (128 mm)6.0 in (151 mm)+1.0 in (+23 mm)+18.63%
Wheel (rim) diameter21.0 in (533 mm)20.0 in (508 mm)-1.0 in (-25 mm)-4.76%
Overall diameter31.0 in (788 mm)31.9 in (811 mm)+0.9 in (+23 mm)+2.80%
Circumference97.5 in (2477 mm)100.2 in (2546 mm)+2.7 in (+69 mm)+2.80%
Revolutions per mile650632-18-2.73%

Differences are 275/55R20 minus 255/50R21; percentages are relative to 255/50R21. These are nominal design dimensions. Real tires vary by brand, tread depth, wheel width, load and pressure.

The overall diameter differs by 2.80%, which is within the common 3% rule of thumb.

The rule of thumb keeps a replacement size within about 3% of the original overall diameter. It covers diameter only. It is not a fit, load or safety check, because width, wheel diameter, load capacity and clearance matter too. Confirm any size change with your vehicle's owner's manual or a tire professional.

Speedometer difference

When the speedometer reads 60 mph on a vehicle built for 255/50R21, the actual speed on 275/55R20 is about 61.7 mph. When it reads 60 mph on a vehicle built for 275/55R20, the actual speed on 255/50R21 is about 58.4 mph. These figures assume the speedometer is accurate on the original size and use nominal dimensions, so treat them as estimates.

Actual speed for a given speedometer reading, 255/50R21 against 275/55R20
Speedometer readsActual on 275/55R20 (built for 255/50R21)Actual on 255/50R21 (built for 275/55R20)
20 mph20.6 mph19.5 mph
30 mph30.8 mph29.2 mph
40 mph41.1 mph38.9 mph
50 mph51.4 mph48.6 mph
60 mph61.7 mph58.4 mph
70 mph72.0 mph68.1 mph
80 mph82.2 mph77.8 mph

A common rule of thumb is to keep a replacement size within about 3% of the original overall diameter. Check the tire placard on the driver's door jamb and your owner's manual for the sizes your vehicle was built for. Confirm any size change with your vehicle's owner's manual or a tire professional.

Which vehicles use each size?

These vehicles list the size among their verified sizes, by trim. Open one to see all of its sizes.

Check it in the calculator

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Shop for 255/50R21 or 275/55R20 tires

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Other comparisons with 255/50R21

Side-by-side dimensions and speedometer difference for sizes close to 255/50R21 in overall diameter.

Other comparisons with 275/55R20

Side-by-side dimensions and speedometer difference for sizes close to 275/55R20 in overall diameter.

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