305/70R16 vs 255/85R16

255/85R16 is 0.26 in (6.5 mm) taller than 305/70R16, a +0.78% diameter difference. With the speedometer set for 305/70R16, an indicated 60 mph is 60.5 mph on 255/85R16.

Is this a safe swap?

Diameter difference +0.78%: under 1%

By overall diameter alone, 255/85R16 is a near match for 305/70R16; the speedometer changes by less than 1%. 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.

305/70R16 vs 255/85R16 differences
Measurement	305/70R16	255/85R16	Difference	% diff
Overall diameter	32.81 in (833.4 mm)	33.07 in (839.9 mm)	+0.26 in (+6.5 mm)	+0.78%
Sidewall height	8.41 in (213.5 mm)	8.53 in (216.8 mm)	+0.13 in (+3.3 mm)	+1.52%
Section width	12.01 in (305.0 mm)	10.04 in (255.0 mm)	−1.97 in (−50.0 mm)	−16.39%
Circumference	103.08 in (2,618.2 mm)	103.88 in (2,638.6 mm)	+0.80 in (+20.4 mm)	+0.78%
Revolutions per mile	615	610	−5	−0.77%

True speed with the speedometer calibrated for 305/70R16
Indicated	Actual on 305/70R16	Actual on 255/85R16	Difference
30 mph	30.0 mph	30.2 mph	+0.2 mph
60 mph	60.0 mph	60.5 mph	+0.5 mph
75 mph	75.0 mph	75.6 mph	+0.6 mph

Ride-height change: 255/85R16 raises the vehicle by 0.13 in (3.3 mm) at the axle (half the +6.5 mm diameter difference).

255/85R16 is 0.26 in taller than 305/70R16 and 50 mm narrower, a 0.78% difference in overall diameter.

With the speedometer calibrated for 305/70R16, an indicated 60 mph is actually 60.5 mph on 255/85R16, and revolutions per mile change from 615 to 610.

Both sizes mount on 16-inch wheels.

Size pages

Other comparisons with 305/70R16

Other comparisons with 255/85R16

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