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245/75R18 vs 255/75R17 tire size comparison

245/75R18255/75R17

255/75R17 is 0.4 in (1.26%) shorter than 245/75R18 and 0.4 in wider. They fit different wheels: 245/75R18 an 18-inch wheel and 255/75R17 a 17-inch wheel.

245/75R18 and 255/75R17 side by side

-0.4 in / -1.26%245/75R18: 32.5 in tall, solid line255/75R17: 32.1 in tall, dashed line245/75R18Width 9.6 in (245 mm)Sidewall 7.2 in (184 mm)255/75R17Width 10.0 in (255 mm)Sidewall 7.5 in (191 mm)
245/75R18 is drawn with a solid line and 255/75R17 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 245/75R18 and 255/75R17, with the difference (255/75R17 minus 245/75R18)
Measurement245/75R18255/75R17DifferenceDifference %
Section width9.6 in (245 mm)10.0 in (255 mm)+0.4 in (+10 mm)+4.08%
Sidewall height7.2 in (184 mm)7.5 in (191 mm)+0.3 in (+7 mm)+4.08%
Wheel (rim) diameter18.0 in (457 mm)17.0 in (432 mm)-1.0 in (-25 mm)-5.56%
Overall diameter32.5 in (825 mm)32.1 in (814 mm)-0.4 in (-11 mm)-1.26%
Circumference102.0 in (2591 mm)100.7 in (2558 mm)-1.3 in (-33 mm)-1.26%
Revolutions per mile621629+8+1.28%

Differences are 255/75R17 minus 245/75R18; percentages are relative to 245/75R18. These are nominal design dimensions. Real tires vary by brand, tread depth, wheel width, load and pressure.

The overall diameter differs by 1.26%, 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 245/75R18, the actual speed on 255/75R17 is about 59.2 mph. When it reads 60 mph on a vehicle built for 255/75R17, the actual speed on 245/75R18 is about 60.8 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, 245/75R18 against 255/75R17
Speedometer readsActual on 255/75R17 (built for 245/75R18)Actual on 245/75R18 (built for 255/75R17)
20 mph19.7 mph20.3 mph
30 mph29.6 mph30.4 mph
40 mph39.5 mph40.5 mph
50 mph49.4 mph50.6 mph
60 mph59.2 mph60.8 mph
70 mph69.1 mph70.9 mph
80 mph79.0 mph81.0 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

The calculator takes the same two sizes and shows the full comparison, or lets you swap either one for another size.

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Shop for 245/75R18 or 255/75R17 tires

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Other comparisons with 245/75R18

Side-by-side dimensions and speedometer difference for sizes close to 245/75R18 in overall diameter.

Other comparisons with 255/75R17

Side-by-side dimensions and speedometer difference for sizes close to 255/75R17 in overall diameter.

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