TireSizesFinder

305/65R17 vs 33x12.50R18

33x12.50R18 is 0.39 in (9.9 mm) taller than 305/65R17, a +1.20% diameter difference. With the speedometer set for 305/65R17, an indicated 60 mph is 60.7 mph on 33x12.50R18.

Is this a safe swap?

Diameter difference +1.20%: within the ±3% guideline

By overall diameter alone, 33x12.50R18 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 33x12.50R18 (33.00 in)305/65R1732.61 in × 12.01 in33x12.50R1833.00 in × 12.50 in
Side profile and tread width, drawn to the same scale.
305/65R17 vs 33x12.50R18 differences
Measurement305/65R1733x12.50R18Difference% diff
Overall diameter32.61 in (828.3 mm)33.00 in (838.2 mm)+0.39 in (+9.9 mm)+1.20%
Sidewall height7.81 in (198.3 mm)7.50 in (190.5 mm)−0.31 in (−7.7 mm)−3.91%
Section width12.01 in (305.0 mm)12.50 in (317.5 mm)+0.49 in (+12.5 mm)+4.10%
Circumference102.45 in (2,602.2 mm)103.67 in (2,633.3 mm)+1.22 in (+31.1 mm)+1.20%
Revolutions per mile618611−7−1.18%
True speed with the speedometer calibrated for 305/65R17
IndicatedActual on 305/65R17Actual on 33x12.50R18Difference
30 mph30.0 mph30.4 mph+0.4 mph
60 mph60.0 mph60.7 mph+0.7 mph
75 mph75.0 mph75.9 mph+0.9 mph

Ride-height change: 33x12.50R18 raises the vehicle by 0.19 in (5.0 mm) at the axle (half the +9.9 mm diameter difference).

33x12.50R18 is 0.39 in taller than 305/65R17 and 13 mm wider, a 1.20% difference in overall diameter.

With the speedometer calibrated for 305/65R17, an indicated 60 mph is actually 60.7 mph on 33x12.50R18, and revolutions per mile change from 618 to 611.

33x12.50R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 305/65R17.

Size pages

Other comparisons with 305/65R17

Other comparisons with 33x12.50R18

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