Tire RulerWhat changes when you switch to 305/55R20
- Height: +1.20″ (+3.8%), so ground clearance at the axle goes up 0.60″.
- Width: ±0.00″ (0 mm). A small change; clearance problems are unlikely if the height fits.
- Sidewall: +0.60″. A taller sidewall rides a bit softer and protects the wheel off-road.
- Revolutions per mile: 630 → 607. Your gears act about 3.8% taller; at 65 mph in a 0.69 top gear with 3.73s, that’s 1,757 → 1,693 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 305/55R20 than 305/50R20?
305/55R20 is 1.20 inches (3.8%) taller and 0.00 inches wider: 33.2" × 12.0" versus 32.0" × 12.0".
Will 305/55R20 change my speedometer?
Yes, by 3.8%. Going from 305/50R20 to 305/55R20, an indicated 60 mph is about 62.3 mph.
Can I replace 305/50R20 with 305/55R20?
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 305/50R20 to 305/55R20?
Usually not for a 3.8% change. With 3.73 gears, the 305/55R20 acts like 3.60.