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LT305/70R18 vs LT315/70R17 tire size comparison

LT305/70R18LT315/70R17

LT315/70R17 is 0.4 in (1.29%) shorter than LT305/70R18 and 0.4 in wider. They fit different wheels: LT305/70R18 an 18-inch wheel and LT315/70R17 a 17-inch wheel.

LT305/70R18 and LT315/70R17 side by side

-0.4 in / -1.29%LT305/70R18: 34.8 in tall, solid lineLT315/70R17: 34.4 in tall, dashed lineLT305/70R18Width 12.0 in (305 mm)Sidewall 8.4 in (214 mm)LT315/70R17Width 12.4 in (315 mm)Sidewall 8.7 in (221 mm)
LT305/70R18 is drawn with a solid line and LT315/70R17 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 LT305/70R18 and LT315/70R17, with the difference (LT315/70R17 minus LT305/70R18)
MeasurementLT305/70R18LT315/70R17DifferenceDifference %
Section width12.0 in (305 mm)12.4 in (315 mm)+0.4 in (+10 mm)+3.28%
Sidewall height8.4 in (214 mm)8.7 in (221 mm)+0.3 in (+7 mm)+3.28%
Wheel (rim) diameter18.0 in (457 mm)17.0 in (432 mm)-1.0 in (-25 mm)-5.56%
Overall diameter34.8 in (884 mm)34.4 in (873 mm)-0.4 in (-11 mm)-1.29%
Circumference109.4 in (2778 mm)108.0 in (2742 mm)-1.4 in (-36 mm)-1.29%
Revolutions per mile579587+8+1.31%

Differences are LT315/70R17 minus LT305/70R18; percentages are relative to LT305/70R18. These are nominal design dimensions. Real tires vary by brand, tread depth, wheel width, load and pressure.

The overall diameter differs by 1.29%, 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 LT305/70R18, the actual speed on LT315/70R17 is about 59.2 mph. When it reads 60 mph on a vehicle built for LT315/70R17, the actual speed on LT305/70R18 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, LT305/70R18 against LT315/70R17
Speedometer readsActual on LT315/70R17 (built for LT305/70R18)Actual on LT305/70R18 (built for LT315/70R17)
20 mph19.7 mph20.3 mph
30 mph29.6 mph30.4 mph
40 mph39.5 mph40.5 mph
50 mph49.4 mph50.7 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.

Open this comparison in the calculator

Shop for LT305/70R18 or LT315/70R17 tires

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Other comparisons with LT305/70R18

Side-by-side dimensions and speedometer difference for sizes close to LT305/70R18 in overall diameter.

Other comparisons with LT315/70R17

Side-by-side dimensions and speedometer difference for sizes close to LT315/70R17 in overall diameter.

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