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215/45R17 vs 225/40R18 tire size comparison

215/45R17225/40R18

225/40R18 is 0.5 in (1.90%) taller than 215/45R17 and 0.4 in wider. They fit different wheels: 215/45R17 a 17-inch wheel and 225/40R18 an 18-inch wheel.

215/45R17 and 225/40R18 side by side

+0.5 in / +1.90%215/45R17: 24.6 in tall, solid line225/40R18: 25.1 in tall, dashed line215/45R17Width 8.5 in (215 mm)Sidewall 3.8 in (97 mm)225/40R18Width 8.9 in (225 mm)Sidewall 3.5 in (90 mm)
215/45R17 is drawn with a solid line and 225/40R18 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 215/45R17 and 225/40R18, with the difference (225/40R18 minus 215/45R17)
Measurement215/45R17225/40R18DifferenceDifference %
Section width8.5 in (215 mm)8.9 in (225 mm)+0.4 in (+10 mm)+4.65%
Sidewall height3.8 in (97 mm)3.5 in (90 mm)-0.3 in (-7 mm)-6.98%
Wheel (rim) diameter17.0 in (432 mm)18.0 in (457 mm)+1.0 in (+25 mm)+5.88%
Overall diameter24.6 in (625 mm)25.1 in (637 mm)+0.5 in (+12 mm)+1.90%
Circumference77.3 in (1964 mm)78.8 in (2002 mm)+1.5 in (+38 mm)+1.90%
Revolutions per mile819804-15-1.87%

Differences are 225/40R18 minus 215/45R17; percentages are relative to 215/45R17. These are nominal design dimensions. Real tires vary by brand, tread depth, wheel width, load and pressure.

The overall diameter differs by 1.90%, 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 215/45R17, the actual speed on 225/40R18 is about 61.1 mph. When it reads 60 mph on a vehicle built for 225/40R18, the actual speed on 215/45R17 is about 58.9 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, 215/45R17 against 225/40R18
Speedometer readsActual on 225/40R18 (built for 215/45R17)Actual on 215/45R17 (built for 225/40R18)
20 mph20.4 mph19.6 mph
30 mph30.6 mph29.4 mph
40 mph40.8 mph39.3 mph
50 mph51.0 mph49.1 mph
60 mph61.1 mph58.9 mph
70 mph71.3 mph68.7 mph
80 mph81.5 mph78.5 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 215/45R17 or 225/40R18 tires

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Other comparisons with 215/45R17

Side-by-side dimensions and speedometer difference for sizes close to 215/45R17 in overall diameter.

Other comparisons with 225/40R18

Side-by-side dimensions and speedometer difference for sizes close to 225/40R18 in overall diameter.

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