Tire RulerWhat changes when you switch to 285/55R20
- Height: +0.33″ (+1.0%), so ground clearance at the axle goes up 0.17″.
- Width: −0.79″ (-20 mm). Check inner clearance to the suspension and frame, and the fender liner at full lock.
- Sidewall: +0.17″. A taller sidewall rides a bit softer and protects the wheel off-road.
- Revolutions per mile: 630 → 624. Your gears act about 1.0% taller; at 65 mph in a 0.69 top gear with 3.73s, that’s 1,757 → 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.
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Frequently asked questions
How much bigger is 285/55R20 than 305/50R20?
285/55R20 is 0.33 inches (1.0%) taller and 0.79 inches narrower: 32.3" × 11.2" versus 32.0" × 12.0".
Will 285/55R20 change my speedometer?
Yes, by 1.0%. Going from 305/50R20 to 285/55R20, an indicated 60 mph is about 60.6 mph.
Can I replace 305/50R20 with 285/55R20?
Often, yes: the height difference is within the ±3% most tire shops accept. Both fit a 20" wheel; confirm the rim width, load index and clearance for your vehicle.
Do I need to regear going from 305/50R20 to 285/55R20?
Usually not for a 1.0% change. With 3.73 gears, the 285/55R20 acts like 3.69.