255/55R19 vs 295/40R21

295/40R21 is 0.25 in (6.3 mm) taller than 255/55R19, a +0.83% diameter difference. With the speedometer set for 255/55R19, an indicated 60 mph is 60.5 mph on 295/40R21.

Is this a safe swap?

Diameter difference +0.83%: under 1%

By overall diameter alone, 295/40R21 is a near match for 255/55R19; 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.

255/55R19 vs 295/40R21 differences
Measurement	255/55R19	295/40R21	Difference	% diff
Overall diameter	30.04 in (763.1 mm)	30.29 in (769.4 mm)	+0.25 in (+6.3 mm)	+0.83%
Sidewall height	5.52 in (140.3 mm)	4.65 in (118.0 mm)	−0.88 in (−22.2 mm)	−15.86%
Section width	10.04 in (255.0 mm)	11.61 in (295.0 mm)	+1.57 in (+40.0 mm)	+15.69%
Circumference	94.38 in (2,397.3 mm)	95.16 in (2,417.1 mm)	+0.78 in (+19.8 mm)	+0.83%
Revolutions per mile	671	666	−5	−0.82%

True speed with the speedometer calibrated for 255/55R19
Indicated	Actual on 255/55R19	Actual on 295/40R21	Difference
30 mph	30.0 mph	30.2 mph	+0.2 mph
60 mph	60.0 mph	60.5 mph	+0.5 mph
75 mph	75.0 mph	75.6 mph	+0.6 mph

Ride-height change: 295/40R21 raises the vehicle by 0.12 in (3.2 mm) at the axle (half the +6.3 mm diameter difference).

295/40R21 is 0.25 in taller than 255/55R19 and 40 mm wider, a 0.83% difference in overall diameter.

With the speedometer calibrated for 255/55R19, an indicated 60 mph is actually 60.5 mph on 295/40R21, and revolutions per mile change from 671 to 666.

295/40R21 mounts on a 21-inch wheel, a plus-2 fitment from the 19-inch wheel of 255/55R19.

Size pages

Other comparisons with 255/55R19

Other comparisons with 295/40R21

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