275/35R18 vs 285/35R18

285/35R18 is 0.28 in (7.0 mm) taller than 275/35R18, a +1.08% diameter difference. With the speedometer set for 275/35R18, an indicated 60 mph is 60.6 mph on 285/35R18.

Is this a safe swap?

Diameter difference +1.08%: within the ±3% guideline

By overall diameter alone, 285/35R18 falls inside the ±3% range commonly used as a guideline when replacing 275/35R18. 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.

275/35R18 vs 285/35R18 differences
Measurement	275/35R18	285/35R18	Difference	% diff
Overall diameter	25.58 in (649.7 mm)	25.85 in (656.7 mm)	+0.28 in (+7.0 mm)	+1.08%
Sidewall height	3.79 in (96.3 mm)	3.93 in (99.8 mm)	+0.14 in (+3.5 mm)	+3.64%
Section width	10.83 in (275.0 mm)	11.22 in (285.0 mm)	+0.39 in (+10.0 mm)	+3.64%
Circumference	80.36 in (2,041.1 mm)	81.22 in (2,063.1 mm)	+0.87 in (+22.0 mm)	+1.08%
Revolutions per mile	788	780	−8	−1.07%

True speed with the speedometer calibrated for 275/35R18
Indicated	Actual on 275/35R18	Actual on 285/35R18	Difference
30 mph	30.0 mph	30.3 mph	+0.3 mph
60 mph	60.0 mph	60.6 mph	+0.6 mph
75 mph	75.0 mph	75.8 mph	+0.8 mph

Ride-height change: 285/35R18 raises the vehicle by 0.14 in (3.5 mm) at the axle (half the +7.0 mm diameter difference).

285/35R18 is 0.28 in taller than 275/35R18 and 10 mm wider, a 1.08% difference in overall diameter.

With the speedometer calibrated for 275/35R18, an indicated 60 mph is actually 60.6 mph on 285/35R18, and revolutions per mile change from 788 to 780.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 275/35R18

Other comparisons with 285/35R18

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