Tire RulerWhat changes when you switch to 245/75R17
- Height: +0.41″ (+1.3%), so ground clearance at the axle goes up 0.21″.
- Width: −0.39″ (-10 mm). Check inner clearance to the suspension and frame, and the fender liner at full lock.
- Sidewall: +0.21″. A taller sidewall rides a bit softer and protects the wheel off-road.
- Revolutions per mile: 649 → 641. Your gears act about 1.3% taller; at 65 mph in a 0.69 top gear with 3.73s, that’s 1,811 → 1,787 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 245/75R17 than 255/70R17?
245/75R17 is 0.41 inches (1.3%) taller and 0.39 inches narrower: 31.5" × 9.6" versus 31.1" × 10.0".
Will 245/75R17 change my speedometer?
Yes, by 1.3%. Going from 255/70R17 to 245/75R17, an indicated 60 mph is about 60.8 mph.
Can I replace 255/70R17 with 245/75R17?
Often, yes: the height difference is within the ±3% most tire shops accept. Both fit a 17" wheel; confirm the rim width, load index and clearance for your vehicle.
Do I need to regear going from 255/70R17 to 245/75R17?
Usually not for a 1.3% change. With 3.73 gears, the 245/75R17 acts like 3.68.