275/45R18 vs 285/45R18

285/45R18 is 0.35 in (9.0 mm) taller than 275/45R18, a +1.28% diameter difference. With the speedometer set for 275/45R18, an indicated 60 mph is 60.8 mph on 285/45R18.

Is this a safe swap?

Diameter difference +1.28%: within the ±3% guideline

By overall diameter alone, 285/45R18 falls inside the ±3% range commonly used as a guideline when replacing 275/45R18. 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.

275/45R18 vs 285/45R18 differences
Measurement	275/45R18	285/45R18	Difference	% diff
Overall diameter	27.74 in (704.7 mm)	28.10 in (713.7 mm)	+0.35 in (+9.0 mm)	+1.28%
Sidewall height	4.87 in (123.8 mm)	5.05 in (128.3 mm)	+0.18 in (+4.5 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	87.16 in (2,213.9 mm)	88.27 in (2,242.2 mm)	+1.11 in (+28.3 mm)	+1.28%
Revolutions per mile	727	718	−9	−1.26%

True speed with the speedometer calibrated for 275/45R18
Indicated	Actual on 275/45R18	Actual on 285/45R18	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: 285/45R18 raises the vehicle by 0.18 in (4.5 mm) at the axle (half the +9.0 mm diameter difference).

285/45R18 is 0.35 in taller than 275/45R18 and 10 mm wider, a 1.28% difference in overall diameter.

With the speedometer calibrated for 275/45R18, an indicated 60 mph is actually 60.8 mph on 285/45R18, and revolutions per mile change from 727 to 718.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 275/45R18

Other comparisons with 285/45R18

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