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245/45R19 vs 315/40R18 tire size comparison

245/45R19315/40R18

315/40R18 is 0.2 in (0.87%) taller than 245/45R19 and 2.8 in wider. They fit different wheels: 245/45R19 a 19-inch wheel and 315/40R18 an 18-inch wheel.

245/45R19 and 315/40R18 side by side

+0.2 in / +0.87%245/45R19: 27.7 in tall, solid line315/40R18: 27.9 in tall, dashed line245/45R19Width 9.6 in (245 mm)Sidewall 4.3 in (110 mm)315/40R18Width 12.4 in (315 mm)Sidewall 5.0 in (126 mm)
245/45R19 is drawn with a solid line and 315/40R18 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 245/45R19 and 315/40R18, with the difference (315/40R18 minus 245/45R19)
Measurement245/45R19315/40R18DifferenceDifference %
Section width9.6 in (245 mm)12.4 in (315 mm)+2.8 in (+70 mm)+28.57%
Sidewall height4.3 in (110 mm)5.0 in (126 mm)+0.7 in (+16 mm)+14.29%
Wheel (rim) diameter19.0 in (483 mm)18.0 in (457 mm)-1.0 in (-26 mm)-5.26%
Overall diameter27.7 in (703 mm)27.9 in (709 mm)+0.2 in (+6 mm)+0.87%
Circumference87.0 in (2209 mm)87.7 in (2228 mm)+0.7 in (+19 mm)+0.87%
Revolutions per mile729722-7-0.86%

Differences are 315/40R18 minus 245/45R19; percentages are relative to 245/45R19. These are nominal design dimensions. Real tires vary by brand, tread depth, wheel width, load and pressure.

The overall diameter differs by 0.87%, 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 245/45R19, the actual speed on 315/40R18 is about 60.5 mph. When it reads 60 mph on a vehicle built for 315/40R18, the actual speed on 245/45R19 is about 59.5 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, 245/45R19 against 315/40R18
Speedometer readsActual on 315/40R18 (built for 245/45R19)Actual on 245/45R19 (built for 315/40R18)
20 mph20.2 mph19.8 mph
30 mph30.3 mph29.7 mph
40 mph40.3 mph39.7 mph
50 mph50.4 mph49.6 mph
60 mph60.5 mph59.5 mph
70 mph70.6 mph69.4 mph
80 mph80.7 mph79.3 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 245/45R19 or 315/40R18 tires

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Other comparisons with 245/45R19

Side-by-side dimensions and speedometer difference for sizes close to 245/45R19 in overall diameter.

Other comparisons with 315/40R18

Side-by-side dimensions and speedometer difference for sizes close to 315/40R18 in overall diameter.

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