275/60R20 vs 285/60R20
Switching from 275/60R20 to 285/60R20 changes the overall diameter by +12.0 mm (+1.4%) — inside the commonly used ±3% guideline. Every figure below is calculated from the two size codes with the standard formulas.
| Measurement | 275/60R20 | 285/60R20 | Difference |
|---|---|---|---|
| Overall diameter | 838.0 mm | 850.0 mm | +12.0 mm (+1.4%) |
| Overall diameter | 32.99 in | 33.46 in | +0.47 in |
| Tire width | 275 mm (10.83 in) | 285 mm (11.22 in) | +10 mm |
| Sidewall height | 165.0 mm (6.50 in) | 171.0 mm (6.73 in) | +6.0 mm |
| Wheel (rim) diameter | 20.0 in | 20.0 in | 0.0 in |
| Circumference | 2633 mm | 2670 mm | +38 mm |
| Revolutions per mile | 1920 | 1893 | -27 |
| Revolutions per km | 380 | 374 | -5 |
Speedometer error
Calibrated for 275/60R20, the speedometer under-reads or over-reads once 285/60R20 is fitted. This is your real speed at each indicated speed:
| Speedometer shows | Actual speed on 285/60R20 | Error |
|---|---|---|
| 20 mph | 20.3 mph | +0.3 mph |
| 40 mph | 40.6 mph | +0.6 mph |
| 60 mph | 60.9 mph | +0.9 mph |
| 80 mph | 81.1 mph | +1.1 mph |
| 100 mph | 101.4 mph | +1.4 mph |
How these two sizes are worked out
275/60R20 breaks down as a 275 mm tread width with a sidewall of 60% of that width (165.0 mm) on a 20.0-inch wheel, giving an overall diameter of 838.0 mm (32.99 in). 285/60R20 works out to 850.0 mm (33.46 in) the same way. The standard formulas are the same ones used on the tire size calculator page: diameter = rim × 25.4 + 2 × sidewall, circumference = π × diameter, revolutions per mile = 63,360 ÷ diameter in inches.
Nominal sizes vary slightly between brands and models, and tread wear shrinks a tire over its life. These figures follow the size codes exactly; your vehicle manual or a professional tire shop is the authority for what fits your vehicle.
More comparisons
Frequently asked questions
Can I replace 275/60R20 tires with 285/60R20?
The diameter change is +1.4%, which is within the commonly used ±3% guideline. Diameter is only one part of fitment — wheel width range, load index, speed rating and physical clearance all have to check out too, so confirm with your vehicle manual or a professional tire shop before buying.
Will 285/60R20 make my speedometer read wrong?
Yes, by the diameter ratio. When the dial shows 60 mph you are really doing 60.9 mph on 285/60R20. The full table above covers 20 to 100 mph.
Which tire is taller, 275/60R20 or 285/60R20?
285/60R20 is taller — 850.0 mm against 838.0 mm overall diameter, a difference of 12.0 mm.