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235/45R18 vs 315/30R19 tire size comparison

235/45R18315/30R19

315/30R19 is 0.1 in (0.43%) taller than 235/45R18 and 3.1 in wider. They fit different wheels: 235/45R18 an 18-inch wheel and 315/30R19 a 19-inch wheel.

235/45R18 and 315/30R19 side by side

+0.1 in / +0.43%235/45R18: 26.3 in tall, solid line315/30R19: 26.4 in tall, dashed line235/45R18Width 9.3 in (235 mm)Sidewall 4.2 in (106 mm)315/30R19Width 12.4 in (315 mm)Sidewall 3.7 in (95 mm)
235/45R18 is drawn with a solid line and 315/30R19 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 235/45R18 and 315/30R19, with the difference (315/30R19 minus 235/45R18)
Measurement235/45R18315/30R19DifferenceDifference %
Section width9.3 in (235 mm)12.4 in (315 mm)+3.1 in (+80 mm)+34.04%
Sidewall height4.2 in (106 mm)3.7 in (95 mm)-0.5 in (-11 mm)-10.64%
Wheel (rim) diameter18.0 in (457 mm)19.0 in (483 mm)+1.0 in (+26 mm)+5.56%
Overall diameter26.3 in (669 mm)26.4 in (672 mm)+0.1 in (+3 mm)+0.43%
Circumference82.7 in (2101 mm)83.1 in (2110 mm)+0.4 in (+9 mm)+0.43%
Revolutions per mile766763-3-0.43%

Differences are 315/30R19 minus 235/45R18; percentages are relative to 235/45R18. These are nominal design dimensions. Real tires vary by brand, tread depth, wheel width, load and pressure.

The overall diameter differs by 0.43%, 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 235/45R18, the actual speed on 315/30R19 is about 60.3 mph. When it reads 60 mph on a vehicle built for 315/30R19, the actual speed on 235/45R18 is about 59.7 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, 235/45R18 against 315/30R19
Speedometer readsActual on 315/30R19 (built for 235/45R18)Actual on 235/45R18 (built for 315/30R19)
20 mph20.1 mph19.9 mph
30 mph30.1 mph29.9 mph
40 mph40.2 mph39.8 mph
50 mph50.2 mph49.8 mph
60 mph60.3 mph59.7 mph
70 mph70.3 mph69.7 mph
80 mph80.3 mph79.7 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 235/45R18 or 315/30R19 tires

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Other comparisons with 235/45R18

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

Other comparisons with 315/30R19

Side-by-side dimensions and speedometer difference for sizes close to 315/30R19 in overall diameter.

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