245/40R17 vs 255/30R19

255/30R19 is 0.31 in (7.8 mm) taller than 245/40R17, a +1.24% diameter difference. With the speedometer set for 245/40R17, an indicated 60 mph is 60.7 mph on 255/30R19.

Is this a safe swap?

Diameter difference +1.24%: within the ±3% guideline

By overall diameter alone, 255/30R19 falls inside the ±3% range commonly used as a guideline when replacing 245/40R17. 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.

245/40R17 vs 255/30R19 differences
Measurement	245/40R17	255/30R19	Difference	% diff
Overall diameter	24.72 in (627.8 mm)	25.02 in (635.6 mm)	+0.31 in (+7.8 mm)	+1.24%
Sidewall height	3.86 in (98.0 mm)	3.01 in (76.5 mm)	−0.85 in (−21.5 mm)	−21.94%
Section width	9.65 in (245.0 mm)	10.04 in (255.0 mm)	+0.39 in (+10.0 mm)	+4.08%
Circumference	77.65 in (1,972.3 mm)	78.61 in (1,996.8 mm)	+0.96 in (+24.5 mm)	+1.24%
Revolutions per mile	816	806	−10	−1.23%

True speed with the speedometer calibrated for 245/40R17
Indicated	Actual on 245/40R17	Actual on 255/30R19	Difference
30 mph	30.0 mph	30.4 mph	+0.4 mph
60 mph	60.0 mph	60.7 mph	+0.7 mph
75 mph	75.0 mph	75.9 mph	+0.9 mph

Ride-height change: 255/30R19 raises the vehicle by 0.15 in (3.9 mm) at the axle (half the +7.8 mm diameter difference).

255/30R19 is 0.31 in taller than 245/40R17 and 10 mm wider, a 1.24% difference in overall diameter.

With the speedometer calibrated for 245/40R17, an indicated 60 mph is actually 60.7 mph on 255/30R19, and revolutions per mile change from 816 to 806.

255/30R19 mounts on a 19-inch wheel, a plus-2 fitment from the 17-inch wheel of 245/40R17.

Size pages

Other comparisons with 245/40R17

Other comparisons with 255/30R19

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