Tire RulerWhat changes when you switch to 285/55R20
- Height: +1.30″ (+4.2%), so ground clearance at the axle goes up 0.65″.
- Width: +1.18″ (30 mm). Check inner clearance to the suspension and frame, and the fender liner at full lock.
- Sidewall: +0.65″. A taller sidewall rides a bit softer and protects the wheel off-road.
- Revolutions per mile: 650 → 624. Your gears act about 4.2% taller; at 65 mph in a 0.69 top gear with 3.73s, that’s 1,811 → 1,739 RPM.
Sizes are theoretical, from the sidewall code. The same size can differ by a few tenths of an inch between brands and tread patterns; check the maker’s spec sheet for the exact model.
Other comparisons
Frequently asked questions
How much bigger is 285/55R20 than 255/55R20?
285/55R20 is 1.30 inches (4.2%) taller and 1.18 inches wider: 32.3" × 11.2" versus 31.0" × 10.0".
Will 285/55R20 change my speedometer?
Yes, by 4.2%. Going from 255/55R20 to 285/55R20, an indicated 60 mph is about 62.5 mph.
Can I replace 255/55R20 with 285/55R20?
Possibly, but the height difference is over 3%, so check clearance and plan to recalibrate the speedometer. Both fit a 20" wheel; confirm the rim width, load index and clearance for your vehicle.
Do I need to regear going from 255/55R20 to 285/55R20?
It's worth considering. To restore 3.73 gearing you'd need about 3.89 (3.73 or 3.92).