295/40R21 vs 265/45R21

265/45R21 is 0.10 in (2.5 mm) taller than 295/40R21, a +0.32% diameter difference. With the speedometer set for 295/40R21, an indicated 60 mph is 60.2 mph on 265/45R21.

Is this a safe swap?

Diameter difference +0.32%: under 1%

By overall diameter alone, 265/45R21 is a near match for 295/40R21; 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.

295/40R21 vs 265/45R21 differences
Measurement	295/40R21	265/45R21	Difference	% diff
Overall diameter	30.29 in (769.4 mm)	30.39 in (771.9 mm)	+0.10 in (+2.5 mm)	+0.32%
Sidewall height	4.65 in (118.0 mm)	4.69 in (119.3 mm)	+0.05 in (+1.3 mm)	+1.06%
Section width	11.61 in (295.0 mm)	10.43 in (265.0 mm)	−1.18 in (−30.0 mm)	−10.17%
Circumference	95.16 in (2,417.1 mm)	95.47 in (2,425.0 mm)	+0.31 in (+7.9 mm)	+0.32%
Revolutions per mile	666	664	−2	−0.32%

True speed with the speedometer calibrated for 295/40R21
Indicated	Actual on 295/40R21	Actual on 265/45R21	Difference
30 mph	30.0 mph	30.1 mph	+0.1 mph
60 mph	60.0 mph	60.2 mph	+0.2 mph
75 mph	75.0 mph	75.2 mph	+0.2 mph

Ride-height change: 265/45R21 raises the vehicle by 0.05 in (1.3 mm) at the axle (half the +2.5 mm diameter difference).

265/45R21 is 0.10 in taller than 295/40R21 and 30 mm narrower, a 0.32% difference in overall diameter.

With the speedometer calibrated for 295/40R21, an indicated 60 mph is actually 60.2 mph on 265/45R21, and revolutions per mile change from 666 to 664.

Both sizes mount on 21-inch wheels.

Size pages

Other comparisons with 295/40R21

Other comparisons with 265/45R21

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