TireSizesFinder

235/45R21 vs 265/40R21

265/40R21 is 0.02 in (0.5 mm) taller than 235/45R21, a +0.07% diameter difference. With the speedometer set for 235/45R21, an indicated 60 mph is 60.0 mph on 265/40R21.

Is this a safe swap?

Diameter difference +0.07%: under 1%

By overall diameter alone, 265/40R21 is a near match for 235/45R21; 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: 235/45R21 (29.33 in) vs 265/40R21 (29.35 in)235/45R2129.33 in × 9.25 in265/40R2129.35 in × 10.43 in
Side profile and tread width, drawn to the same scale.
235/45R21 vs 265/40R21 differences
Measurement235/45R21265/40R21Difference% diff
Overall diameter29.33 in (744.9 mm)29.35 in (745.4 mm)+0.02 in (+0.5 mm)+0.07%
Sidewall height4.16 in (105.8 mm)4.17 in (106.0 mm)+0.01 in (+0.3 mm)+0.24%
Section width9.25 in (235.0 mm)10.43 in (265.0 mm)+1.18 in (+30.0 mm)+12.77%
Circumference92.13 in (2,340.2 mm)92.19 in (2,341.7 mm)+0.06 in (+1.6 mm)+0.07%
Revolutions per mile6886870−0.07%
True speed with the speedometer calibrated for 235/45R21
IndicatedActual on 235/45R21Actual on 265/40R21Difference
30 mph30.0 mph30.0 mph0.0 mph
60 mph60.0 mph60.0 mph0.0 mph
75 mph75.0 mph75.1 mph+0.1 mph

Ride-height change: 265/40R21 raises the vehicle by 0.01 in (0.3 mm) at the axle (half the +0.5 mm diameter difference).

265/40R21 is 0.02 in taller than 235/45R21 and 30 mm wider, a 0.07% difference in overall diameter.

With the speedometer calibrated for 235/45R21, an indicated 60 mph is actually 60.0 mph on 265/40R21, and revolutions per mile change from 688 to 687.

Both sizes mount on 21-inch wheels.

Size pages

Other comparisons with 235/45R21

Other comparisons with 265/40R21

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