305/65R17 vs 255/80R17

255/80R17 is 0.45 in (11.5 mm) taller than 305/65R17, a +1.39% diameter difference. With the speedometer set for 305/65R17, an indicated 60 mph is 60.8 mph on 255/80R17.

Is this a safe swap?

Diameter difference +1.39%: within the ±3% guideline

By overall diameter alone, 255/80R17 falls inside the ±3% range commonly used as a guideline when replacing 305/65R17. 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.

305/65R17 vs 255/80R17 differences
Measurement	305/65R17	255/80R17	Difference	% diff
Overall diameter	32.61 in (828.3 mm)	33.06 in (839.8 mm)	+0.45 in (+11.5 mm)	+1.39%
Sidewall height	7.81 in (198.3 mm)	8.03 in (204.0 mm)	+0.23 in (+5.8 mm)	+2.90%
Section width	12.01 in (305.0 mm)	10.04 in (255.0 mm)	−1.97 in (−50.0 mm)	−16.39%
Circumference	102.45 in (2,602.2 mm)	103.87 in (2,638.3 mm)	+1.42 in (+36.1 mm)	+1.39%
Revolutions per mile	618	610	−8	−1.37%

True speed with the speedometer calibrated for 305/65R17
Indicated	Actual on 305/65R17	Actual on 255/80R17	Difference
30 mph	30.0 mph	30.4 mph	+0.4 mph
60 mph	60.0 mph	60.8 mph	+0.8 mph
75 mph	75.0 mph	76.0 mph	+1.0 mph

Ride-height change: 255/80R17 raises the vehicle by 0.23 in (5.8 mm) at the axle (half the +11.5 mm diameter difference).

255/80R17 is 0.45 in taller than 305/65R17 and 50 mm narrower, a 1.39% difference in overall diameter.

With the speedometer calibrated for 305/65R17, an indicated 60 mph is actually 60.8 mph on 255/80R17, and revolutions per mile change from 618 to 610.

Both sizes mount on 17-inch wheels.

Size pages

Other comparisons with 305/65R17

Other comparisons with 255/80R17

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