TireSizesFinder

295/40R20 vs 235/45R21

235/45R21 is 0.04 in (0.9 mm) taller than 295/40R20, a +0.12% diameter difference. With the speedometer set for 295/40R20, an indicated 60 mph is 60.1 mph on 235/45R21.

Is this a safe swap?

Diameter difference +0.12%: under 1%

By overall diameter alone, 235/45R21 is a near match for 295/40R20; the speedometer changes by less than 1%. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

To-scale drawing: 295/40R20 (29.29 in) vs 235/45R21 (29.33 in)295/40R2029.29 in × 11.61 in235/45R2129.33 in × 9.25 in
Side profile and tread width, drawn to the same scale.
295/40R20 vs 235/45R21 differences
Measurement295/40R20235/45R21Difference% diff
Overall diameter29.29 in (744.0 mm)29.33 in (744.9 mm)+0.04 in (+0.9 mm)+0.12%
Sidewall height4.65 in (118.0 mm)4.16 in (105.8 mm)−0.48 in (−12.2 mm)−10.38%
Section width11.61 in (295.0 mm)9.25 in (235.0 mm)−2.36 in (−60.0 mm)−20.34%
Circumference92.02 in (2,337.3 mm)92.13 in (2,340.2 mm)+0.11 in (+2.8 mm)+0.12%
Revolutions per mile689688−1−0.12%
True speed with the speedometer calibrated for 295/40R20
IndicatedActual on 295/40R20Actual on 235/45R21Difference
30 mph30.0 mph30.0 mph0.0 mph
60 mph60.0 mph60.1 mph+0.1 mph
75 mph75.0 mph75.1 mph+0.1 mph

Ride-height change: 235/45R21 raises the vehicle by 0.02 in (0.4 mm) at the axle (half the +0.9 mm diameter difference).

235/45R21 is 0.04 in taller than 295/40R20 and 60 mm narrower, a 0.12% difference in overall diameter.

With the speedometer calibrated for 295/40R20, an indicated 60 mph is actually 60.1 mph on 235/45R21, and revolutions per mile change from 689 to 688.

235/45R21 mounts on a 21-inch wheel, a plus-1 fitment from the 20-inch wheel of 295/40R20.

Size pages

Other comparisons with 295/40R20

Other comparisons with 235/45R21

Source: Calculated from standard tire geometry formulas. Verified . How these numbers are calculated.