Tire RulerWhat changes when you switch to 305/55R20
- Height: +1.30″ (+4.1%), 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: 632 → 607. Your gears act about 4.1% taller; at 65 mph in a 0.69 top gear with 3.73s, that’s 1,762 → 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 275/55R20?
305/55R20 is 1.30 inches (4.1%) taller and 1.18 inches wider: 33.2" × 12.0" versus 31.9" × 10.8".
Will 305/55R20 change my speedometer?
Yes, by 4.1%. Going from 275/55R20 to 305/55R20, an indicated 60 mph is about 62.4 mph.
Can I replace 275/55R20 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 275/55R20 to 305/55R20?
It's worth considering. To restore 3.73 gearing you'd need about 3.88 (3.73 or 3.92).