235/45R17 vs 255/30R19

255/30R19 is 0.30 in (7.7 mm) shorter than 235/45R17, a −1.20% diameter difference. With the speedometer set for 235/45R17, an indicated 60 mph is 59.3 mph on 255/30R19.

Is this a safe swap?

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

By overall diameter alone, 255/30R19 falls inside the ±3% range commonly used as a guideline when replacing 235/45R17. 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.

235/45R17 vs 255/30R19 differences
Measurement	235/45R17	255/30R19	Difference	% diff
Overall diameter	25.33 in (643.3 mm)	25.02 in (635.6 mm)	−0.30 in (−7.7 mm)	−1.20%
Sidewall height	4.16 in (105.8 mm)	3.01 in (76.5 mm)	−1.15 in (−29.2 mm)	−27.66%
Section width	9.25 in (235.0 mm)	10.04 in (255.0 mm)	+0.79 in (+20.0 mm)	+8.51%
Circumference	79.57 in (2,021.0 mm)	78.61 in (1,996.8 mm)	−0.95 in (−24.2 mm)	−1.20%
Revolutions per mile	796	806	+10	+1.21%

True speed with the speedometer calibrated for 235/45R17
Indicated	Actual on 235/45R17	Actual on 255/30R19	Difference
30 mph	30.0 mph	29.6 mph	−0.4 mph
60 mph	60.0 mph	59.3 mph	−0.7 mph
75 mph	75.0 mph	74.1 mph	−0.9 mph

Ride-height change: 255/30R19 lowers the vehicle by 0.15 in (3.9 mm) at the axle (half the −7.7 mm diameter difference).

255/30R19 is 0.30 in shorter than 235/45R17 and 20 mm wider, a 1.20% difference in overall diameter.

With the speedometer calibrated for 235/45R17, an indicated 60 mph is actually 59.3 mph on 255/30R19, and revolutions per mile change from 796 to 806.

255/30R19 mounts on a 19-inch wheel, a plus-2 fitment from the 17-inch wheel of 235/45R17.

Size pages

Other comparisons with 235/45R17

Other comparisons with 255/30R19

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