255/75R17 vs 305/65R17

305/65R17 is 0.55 in (14.0 mm) taller than 255/75R17, a +1.72% diameter difference. With the speedometer set for 255/75R17, an indicated 60 mph is 61.0 mph on 305/65R17.

Is this a safe swap?

Diameter difference +1.72%: within the ±3% guideline

By overall diameter alone, 305/65R17 falls inside the ±3% range commonly used as a guideline when replacing 255/75R17. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

Side profile and tread width, drawn to the same scale.

255/75R17 vs 305/65R17 differences
Measurement	255/75R17	305/65R17	Difference	% diff
Overall diameter	32.06 in (814.3 mm)	32.61 in (828.3 mm)	+0.55 in (+14.0 mm)	+1.72%
Sidewall height	7.53 in (191.3 mm)	7.81 in (198.3 mm)	+0.28 in (+7.0 mm)	+3.66%
Section width	10.04 in (255.0 mm)	12.01 in (305.0 mm)	+1.97 in (+50.0 mm)	+19.61%
Circumference	100.72 in (2,558.2 mm)	102.45 in (2,602.2 mm)	+1.73 in (+44.0 mm)	+1.72%
Revolutions per mile	629	618	−11	−1.69%

True speed with the speedometer calibrated for 255/75R17
Indicated	Actual on 255/75R17	Actual on 305/65R17	Difference
30 mph	30.0 mph	30.5 mph	+0.5 mph
60 mph	60.0 mph	61.0 mph	+1.0 mph
75 mph	75.0 mph	76.3 mph	+1.3 mph

Ride-height change: 305/65R17 raises the vehicle by 0.28 in (7.0 mm) at the axle (half the +14.0 mm diameter difference).

305/65R17 is 0.55 in taller than 255/75R17 and 50 mm wider, a 1.72% difference in overall diameter.

With the speedometer calibrated for 255/75R17, an indicated 60 mph is actually 61.0 mph on 305/65R17, and revolutions per mile change from 629 to 618.

Both sizes mount on 17-inch wheels.

Size pages

Other comparisons with 255/75R17

Other comparisons with 305/65R17

Source: Calculated from standard tire geometry formulas. Verified 2026-09-27. How these numbers are calculated.