Tire RulerWhat changes when you switch to 305/55R20
- Height: +0.43″ (+1.3%), so ground clearance at the axle goes up 0.22″.
- Width: +0.39″ (10 mm). Check inner clearance to the suspension and frame, and the fender liner at full lock.
- Sidewall: +0.22″. A taller sidewall rides a bit softer and protects the wheel off-road.
- Revolutions per mile: 615 → 607. Your gears act about 1.3% taller; at 65 mph in a 0.69 top gear with 3.73s, that’s 1,716 → 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.
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Frequently asked questions
How much bigger is 305/55R20 than 295/55R20?
305/55R20 is 0.43 inches (1.3%) taller and 0.39 inches wider: 33.2" × 12.0" versus 32.8" × 11.6".
Will 305/55R20 change my speedometer?
Yes, by 1.3%. Going from 295/55R20 to 305/55R20, an indicated 60 mph is about 60.8 mph.
Can I replace 295/55R20 with 305/55R20?
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 295/55R20 to 305/55R20?
Usually not for a 1.3% change. With 3.73 gears, the 305/55R20 acts like 3.68.