235/60R19 vs 255/45R21

255/45R21 is 0.07 in (1.7 mm) shorter than 235/60R19, a −0.22% diameter difference. With the speedometer set for 235/60R19, an indicated 60 mph is 59.9 mph on 255/45R21.

Is this a safe swap?

Diameter difference −0.22%: under 1%

By overall diameter alone, 255/45R21 is a near match for 235/60R19; the speedometer changes by less than 1%. 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.

235/60R19 vs 255/45R21 differences
Measurement	235/60R19	255/45R21	Difference	% diff
Overall diameter	30.10 in (764.6 mm)	30.04 in (762.9 mm)	−0.07 in (−1.7 mm)	−0.22%
Sidewall height	5.55 in (141.0 mm)	4.52 in (114.8 mm)	−1.03 in (−26.2 mm)	−18.62%
Section width	9.25 in (235.0 mm)	10.04 in (255.0 mm)	+0.79 in (+20.0 mm)	+8.51%
Circumference	94.57 in (2,402.1 mm)	94.36 in (2,396.7 mm)	−0.21 in (−5.3 mm)	−0.22%
Revolutions per mile	670	671	+1	+0.22%

True speed with the speedometer calibrated for 235/60R19
Indicated	Actual on 235/60R19	Actual on 255/45R21	Difference
30 mph	30.0 mph	29.9 mph	−0.1 mph
60 mph	60.0 mph	59.9 mph	−0.1 mph
75 mph	75.0 mph	74.8 mph	−0.2 mph

Ride-height change: 255/45R21 lowers the vehicle by 0.03 in (0.8 mm) at the axle (half the −1.7 mm diameter difference).

255/45R21 is 0.07 in shorter than 235/60R19 and 20 mm wider, a 0.22% difference in overall diameter.

With the speedometer calibrated for 235/60R19, an indicated 60 mph is actually 59.9 mph on 255/45R21, and revolutions per mile change from 670 to 671.

255/45R21 mounts on a 21-inch wheel, a plus-2 fitment from the 19-inch wheel of 235/60R19.

Size pages

Other comparisons with 235/60R19

Other comparisons with 255/45R21

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