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325/65R18 vs LT275/65R20 tire size comparison

325/65R18LT275/65R20

LT275/65R20 is 0.5 in (1.61%) shorter than 325/65R18 and 2.0 in narrower. They fit different wheels: 325/65R18 an 18-inch wheel and LT275/65R20 a 20-inch wheel.

325/65R18 and LT275/65R20 side by side

-0.5 in / -1.61%325/65R18: 34.6 in tall, solid lineLT275/65R20: 34.1 in tall, dashed line325/65R18Width 12.8 in (325 mm)Sidewall 8.3 in (211 mm)LT275/65R20Width 10.8 in (275 mm)Sidewall 7.0 in (179 mm)
325/65R18 is drawn with a solid line and LT275/65R20 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 325/65R18 and LT275/65R20, with the difference (LT275/65R20 minus 325/65R18)
Measurement325/65R18LT275/65R20DifferenceDifference %
Section width12.8 in (325 mm)10.8 in (275 mm)-2.0 in (-50 mm)-15.38%
Sidewall height8.3 in (211 mm)7.0 in (179 mm)-1.3 in (-32 mm)-15.38%
Wheel (rim) diameter18.0 in (457 mm)20.0 in (508 mm)+2.0 in (+51 mm)+11.11%
Overall diameter34.6 in (880 mm)34.1 in (866 mm)-0.5 in (-14 mm)-1.61%
Circumference108.8 in (2764 mm)107.0 in (2719 mm)-1.8 in (-45 mm)-1.61%
Revolutions per mile582592+10+1.64%

Differences are LT275/65R20 minus 325/65R18; percentages are relative to 325/65R18. These are nominal design dimensions. Real tires vary by brand, tread depth, wheel width, load and pressure.

The overall diameter differs by 1.61%, 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 325/65R18, the actual speed on LT275/65R20 is about 59.0 mph. When it reads 60 mph on a vehicle built for LT275/65R20, the actual speed on 325/65R18 is about 61.0 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, 325/65R18 against LT275/65R20
Speedometer readsActual on LT275/65R20 (built for 325/65R18)Actual on 325/65R18 (built for LT275/65R20)
20 mph19.7 mph20.3 mph
30 mph29.5 mph30.5 mph
40 mph39.4 mph40.7 mph
50 mph49.2 mph50.8 mph
60 mph59.0 mph61.0 mph
70 mph68.9 mph71.1 mph
80 mph78.7 mph81.3 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 325/65R18 or LT275/65R20 tires

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Other comparisons with 325/65R18

Side-by-side dimensions and speedometer difference for sizes close to 325/65R18 in overall diameter.

Other comparisons with LT275/65R20

Side-by-side dimensions and speedometer difference for sizes close to LT275/65R20 in overall diameter.

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