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215/55R17 vs 235/45R18 tire size comparison

215/55R17235/45R18

235/45R18 is 1 mm (0.06%) taller than 215/55R17 and 0.8 in wider. They fit different wheels: 215/55R17 a 17-inch wheel and 235/45R18 an 18-inch wheel.

215/55R17 and 235/45R18 side by side

0.0 in / +0.06%215/55R17: 26.3 in tall, solid line235/45R18: 26.3 in tall, dashed line215/55R17Width 8.5 in (215 mm)Sidewall 4.7 in (118 mm)235/45R18Width 9.3 in (235 mm)Sidewall 4.2 in (106 mm)
215/55R17 is drawn with a solid line and 235/45R18 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 215/55R17 and 235/45R18, with the difference (235/45R18 minus 215/55R17)
Measurement215/55R17235/45R18DifferenceDifference %
Section width8.5 in (215 mm)9.3 in (235 mm)+0.8 in (+20 mm)+9.30%
Sidewall height4.7 in (118 mm)4.2 in (106 mm)-0.5 in (-12 mm)-10.57%
Wheel (rim) diameter17.0 in (432 mm)18.0 in (457 mm)+1.0 in (+25 mm)+5.88%
Overall diameter26.3 in (668 mm)26.3 in (669 mm)0.0 in (+1 mm)+0.06%
Circumference82.7 in (2100 mm)82.7 in (2101 mm)0.0 in (+1 mm)+0.06%
Revolutions per mile767766-1-0.06%

Differences are 235/45R18 minus 215/55R17; percentages are relative to 215/55R17. These are nominal design dimensions. Real tires vary by brand, tread depth, wheel width, load and pressure.

The overall diameter differs by 0.06%, 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 215/55R17, the actual speed on 235/45R18 is about 60.0 mph. When it reads 60 mph on a vehicle built for 235/45R18, the actual speed on 215/55R17 is about 60.0 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, 215/55R17 against 235/45R18
Speedometer readsActual on 235/45R18 (built for 215/55R17)Actual on 215/55R17 (built for 235/45R18)
20 mph20.0 mph20.0 mph
30 mph30.0 mph30.0 mph
40 mph40.0 mph40.0 mph
50 mph50.0 mph50.0 mph
60 mph60.0 mph60.0 mph
70 mph70.0 mph70.0 mph
80 mph80.0 mph80.0 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.

Open this comparison in the calculator

Shop for 215/55R17 or 235/45R18 tires

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Other comparisons with 215/55R17

Side-by-side dimensions and speedometer difference for sizes close to 215/55R17 in overall diameter.

Other comparisons with 235/45R18

Side-by-side dimensions and speedometer difference for sizes close to 235/45R18 in overall diameter.

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