Tire size comparison
275/55R20 vs 285/55R20 Tires
A 285/55R20 tire is 0.43 inches (1.4%) taller and 0.39 inches wider than a 275/55R20. When the speedometer reads 60 mph after the swap, the true speed is about 60.8 mph. Every figure on this page is calculated from the two size codes.
- +1.4% diameter
- +0.39 in width
- 60.8 mph at 60
- -8.5 revs per mile
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| Current | New | Difference |
|---|
Figures are nominal geometry calculated from the size code. A tire’s real measured diameter varies by brand, model and tread depth; check the manufacturer’s spec sheet before you buy, and confirm clearance, load index and speed rating for your vehicle.
Side-by-side specifications
| 275/55R20 | 285/55R20 | Difference | |
|---|---|---|---|
| Overall diameter | 31.91 in | 32.34 in | +0.43 in (+1.4%) |
| Section width | 10.83 in | 11.22 in | +0.39 in |
| Sidewall height | 5.95 in | 6.17 in | +0.22 in |
| Wheel diameter | 20 in | 20 in | +0 in |
| Circumference | 100.25 in | 101.61 in | +1.36 in |
| Revolutions per mile | 632.0 | 623.6 | -8.5 |
| Ground clearance change | +0.22 in |
Speedometer error at common speeds
The speedometer was calibrated for the original 275/55R20. The 285/55R20 covers 1.4% more ground per turn, so the true speed is higher than the reading.
| Speedometer shows | True speed | Difference |
|---|---|---|
| 25 mph | 25.3 mph | +0.3 mph |
| 35 mph | 35.5 mph | +0.5 mph |
| 45 mph | 45.6 mph | +0.6 mph |
| 55 mph | 55.7 mph | +0.7 mph |
| 60 mph | 60.8 mph | +0.8 mph |
| 65 mph | 65.9 mph | +0.9 mph |
| 70 mph | 71.0 mph | +1.0 mph |
| 75 mph | 76.0 mph | +1.0 mph |
| 80 mph | 81.1 mph | +1.1 mph |
Will a 285/55R20 fit in place of a 275/55R20?
- HeightThe overall diameter changes by +0.43 inches. The tread moves 0.22 inches closer to the fender at the top.
- Ground clearanceThe axle sits about 0.22 inches higher: half the change in diameter.
- WidthOn the same wheel and offset the tire grows 0.20 inches on each side, toward the suspension and toward the fender. Check full steering lock.
- WheelBoth sizes mount on a 20-inch wheel. Confirm your wheel width is inside the approved rim width range in the tire maker's specification sheet.
- Load and speedThe size code does not set load capacity. The new tire must meet the load index and speed rating on your door placard: check the chart.
Frequently asked questions
How much taller is a 285/55R20 than a 275/55R20?
0.43 inches, or 1.4%: 31.91 inches against 32.34 inches of overall diameter, calculated from the size codes. Measured diameters vary slightly by tire model and tread depth, so check the maker's specification for the exact tire.
Will my speedometer be off with 285/55R20 tires?
Yes, by about 1.4%. At an indicated 60 mph you would be doing about 60.8 mph, and at an indicated 70 mph about 71.0 mph. A recalibration tool or a dealer can correct the reading.
Can I mount 285/55R20 tires on the wheels I use for 275/55R20?
The wheel diameter matches (20 inches). Whether your wheel width suits the new tire depends on the approved rim width range published by the tire maker, so check it before you buy.
How many revolutions per mile does a 285/55R20 make?
About 624 revolutions per mile, against 632 for a 275/55R20, calculated from the nominal diameter. The maker's published figure for a specific tire can differ slightly.