TireSizesFinder

305/65R17 vs 275/70R18

275/70R18 is 0.55 in (13.9 mm) taller than 305/65R17, a +1.68% diameter difference. With the speedometer set for 305/65R17, an indicated 60 mph is 61.0 mph on 275/70R18.

Is this a safe swap?

Diameter difference +1.68%: within the ±3% guideline

By overall diameter alone, 275/70R18 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.

To-scale drawing: 305/65R17 (32.61 in) vs 275/70R18 (33.16 in)305/65R1732.61 in × 12.01 in275/70R1833.16 in × 10.83 in
Side profile and tread width, drawn to the same scale.
305/65R17 vs 275/70R18 differences
Measurement305/65R17275/70R18Difference% diff
Overall diameter32.61 in (828.3 mm)33.16 in (842.2 mm)+0.55 in (+13.9 mm)+1.68%
Sidewall height7.81 in (198.3 mm)7.58 in (192.5 mm)−0.23 in (−5.7 mm)−2.90%
Section width12.01 in (305.0 mm)10.83 in (275.0 mm)−1.18 in (−30.0 mm)−9.84%
Circumference102.45 in (2,602.2 mm)104.17 in (2,645.8 mm)+1.72 in (+43.7 mm)+1.68%
Revolutions per mile618608−10−1.65%
True speed with the speedometer calibrated for 305/65R17
IndicatedActual on 305/65R17Actual on 275/70R18Difference
30 mph30.0 mph30.5 mph+0.5 mph
60 mph60.0 mph61.0 mph+1.0 mph
75 mph75.0 mph76.3 mph+1.3 mph

Ride-height change: 275/70R18 raises the vehicle by 0.27 in (7.0 mm) at the axle (half the +13.9 mm diameter difference).

275/70R18 is 0.55 in taller than 305/65R17 and 30 mm narrower, a 1.68% difference in overall diameter.

With the speedometer calibrated for 305/65R17, an indicated 60 mph is actually 61.0 mph on 275/70R18, and revolutions per mile change from 618 to 608.

275/70R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 305/65R17.

Size pages

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