TireSizesFinder

30x9.50R15 vs 255/65R17

255/65R17 is 0.05 in (1.3 mm) taller than 30x9.50R15, a +0.17% diameter difference. With the speedometer set for 30x9.50R15, an indicated 60 mph is 60.1 mph on 255/65R17.

Is this a safe swap?

Diameter difference +0.17%: under 1%

By overall diameter alone, 255/65R17 is a near match for 30x9.50R15; the speedometer changes by less than 1%. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

To-scale drawing: 30x9.50R15 (30.00 in) vs 255/65R17 (30.05 in)30x9.50R1530.00 in × 9.50 in255/65R1730.05 in × 10.04 in
Side profile and tread width, drawn to the same scale.
30x9.50R15 vs 255/65R17 differences
Measurement30x9.50R15255/65R17Difference% diff
Overall diameter30.00 in (762.0 mm)30.05 in (763.3 mm)+0.05 in (+1.3 mm)+0.17%
Sidewall height7.50 in (190.5 mm)6.53 in (165.8 mm)−0.97 in (−24.7 mm)−12.99%
Section width9.50 in (241.3 mm)10.04 in (255.0 mm)+0.54 in (+13.7 mm)+5.68%
Circumference94.25 in (2,393.9 mm)94.41 in (2,398.0 mm)+0.16 in (+4.1 mm)+0.17%
Revolutions per mile672671−1−0.17%
True speed with the speedometer calibrated for 30x9.50R15
IndicatedActual on 30x9.50R15Actual on 255/65R17Difference
30 mph30.0 mph30.1 mph+0.1 mph
60 mph60.0 mph60.1 mph+0.1 mph
75 mph75.0 mph75.1 mph+0.1 mph

Ride-height change: 255/65R17 raises the vehicle by 0.03 in (0.6 mm) at the axle (half the +1.3 mm diameter difference).

255/65R17 is 0.05 in taller than 30x9.50R15 and 14 mm wider, a 0.17% difference in overall diameter.

With the speedometer calibrated for 30x9.50R15, an indicated 60 mph is actually 60.1 mph on 255/65R17, and revolutions per mile change from 672 to 671.

255/65R17 mounts on a 17-inch wheel, a plus-2 fitment from the 15-inch wheel of 30x9.50R15.

Size pages

Other comparisons with 30x9.50R15

Other comparisons with 255/65R17

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