TireSizesFinder

305/70R16 vs 275/70R18

275/70R18 is 0.35 in (8.8 mm) taller than 305/70R16, a +1.06% diameter difference. With the speedometer set for 305/70R16, an indicated 60 mph is 60.6 mph on 275/70R18.

Is this a safe swap?

Diameter difference +1.06%: within the ±3% guideline

By overall diameter alone, 275/70R18 falls inside the ±3% range commonly used as a guideline when replacing 305/70R16. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

To-scale drawing: 305/70R16 (32.81 in) vs 275/70R18 (33.16 in)305/70R1632.81 in × 12.01 in275/70R1833.16 in × 10.83 in
Side profile and tread width, drawn to the same scale.
305/70R16 vs 275/70R18 differences
Measurement305/70R16275/70R18Difference% diff
Overall diameter32.81 in (833.4 mm)33.16 in (842.2 mm)+0.35 in (+8.8 mm)+1.06%
Sidewall height8.41 in (213.5 mm)7.58 in (192.5 mm)−0.83 in (−21.0 mm)−9.84%
Section width12.01 in (305.0 mm)10.83 in (275.0 mm)−1.18 in (−30.0 mm)−9.84%
Circumference103.08 in (2,618.2 mm)104.17 in (2,645.8 mm)+1.09 in (+27.6 mm)+1.06%
Revolutions per mile615608−6−1.04%
True speed with the speedometer calibrated for 305/70R16
IndicatedActual on 305/70R16Actual on 275/70R18Difference
30 mph30.0 mph30.3 mph+0.3 mph
60 mph60.0 mph60.6 mph+0.6 mph
75 mph75.0 mph75.8 mph+0.8 mph

Ride-height change: 275/70R18 raises the vehicle by 0.17 in (4.4 mm) at the axle (half the +8.8 mm diameter difference).

275/70R18 is 0.35 in taller than 305/70R16 and 30 mm narrower, a 1.06% difference in overall diameter.

With the speedometer calibrated for 305/70R16, an indicated 60 mph is actually 60.6 mph on 275/70R18, and revolutions per mile change from 615 to 608.

275/70R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 305/70R16.

Size pages

Other comparisons with 305/70R16

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Source: Calculated from standard tire geometry formulas. Verified . How these numbers are calculated.