275/65R20 vs 325/65R18 tire size comparison
325/65R18 is 0.5 in (1.64%) taller than 275/65R20 and 2.0 in wider. They fit different wheels: 275/65R20 a 20-inch wheel and 325/65R18 an 18-inch wheel.
275/65R20 and 325/65R18 side by side
| Measurement | 275/65R20 | 325/65R18 | Difference | Difference % |
|---|---|---|---|---|
| Section width | 10.8 in (275 mm) | 12.8 in (325 mm) | +2.0 in (+50 mm) | +18.18% |
| Sidewall height | 7.0 in (179 mm) | 8.3 in (211 mm) | +1.3 in (+32 mm) | +18.18% |
| Wheel (rim) diameter | 20.0 in (508 mm) | 18.0 in (457 mm) | -2.0 in (-51 mm) | -10.00% |
| Overall diameter | 34.1 in (866 mm) | 34.6 in (880 mm) | +0.5 in (+14 mm) | +1.64% |
| Circumference | 107.0 in (2719 mm) | 108.8 in (2764 mm) | +1.8 in (+45 mm) | +1.64% |
| Revolutions per mile | 592 | 582 | -10 | -1.61% |
Differences are 325/65R18 minus 275/65R20; percentages are relative to 275/65R20. These are nominal design dimensions. Real tires vary by brand, tread depth, wheel width, load and pressure.
The overall diameter differs by 1.64%, 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 275/65R20, the actual speed on 325/65R18 is about 61.0 mph. When it reads 60 mph on a vehicle built for 325/65R18, the actual speed on 275/65R20 is about 59.0 mph. These figures assume the speedometer is accurate on the original size and use nominal dimensions, so treat them as estimates.
| Speedometer reads | Actual on 325/65R18 (built for 275/65R20) | Actual on 275/65R20 (built for 325/65R18) |
|---|---|---|
| 20 mph | 20.3 mph | 19.7 mph |
| 30 mph | 30.5 mph | 29.5 mph |
| 40 mph | 40.7 mph | 39.4 mph |
| 50 mph | 50.8 mph | 49.2 mph |
| 60 mph | 61.0 mph | 59.0 mph |
| 70 mph | 71.1 mph | 68.9 mph |
| 80 mph | 81.3 mph | 78.7 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.
Open this comparison in the calculatorShop for 275/65R20 or 325/65R18 tires
Confirm the size on your tire sidewall or door placard first. These links open each store's own search; prices and stock are on their sites.
275/65R20
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Other comparisons with 275/65R20
Side-by-side dimensions and speedometer difference for sizes close to 275/65R20 in overall diameter.
- 275/65R20 vs LT315/70R17+0.84% taller than 275/65R20
- 275/65R20 vs 285/70R18-1.07% shorter than 275/65R20
- 265/75R18 vs 275/65R20-1.25% shorter than 275/65R20
- 275/65R20 vs LT305/70R18+2.16% taller than 275/65R20
Other comparisons with 325/65R18
Side-by-side dimensions and speedometer difference for sizes close to 325/65R18 in overall diameter.
- 325/65R18 vs LT305/70R18+0.51% taller than 325/65R18
- 325/65R18 vs LT275/50R24+0.56% taller than 325/65R18
- 285/75R18 vs 325/65R18+0.57% taller than 325/65R18
- 325/65R18 vs LT285/75R18+0.57% taller than 325/65R18
- 325/65R18 vs LT315/70R17-0.78% shorter than 325/65R18
You might also need
- Digital tire pressure gauge (Amazon search, opens in a new tab)
Check your tire pressure against the number on your door placard.
- Portable tire inflator (Amazon search, opens in a new tab)
Top up a low tire at home without a trip to the gas station.
- Tire tread depth gauge (Amazon search, opens in a new tab)
Measure how much tread is left before you decide to replace.
- Lug wrench or torque wrench (Amazon search, opens in a new tab)
Useful for rotations and tire changes; follow the torque spec in your owner's manual.
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