TireSizesFinder

255/45R21 vs 295/40R21

295/40R21 is 0.26 in (6.5 mm) taller than 255/45R21, a +0.85% diameter difference. With the speedometer set for 255/45R21, an indicated 60 mph is 60.5 mph on 295/40R21.

Is this a safe swap?

Diameter difference +0.85%: under 1%

By overall diameter alone, 295/40R21 is a near match for 255/45R21; 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: 255/45R21 (30.04 in) vs 295/40R21 (30.29 in)255/45R2130.04 in × 10.04 in295/40R2130.29 in × 11.61 in
Side profile and tread width, drawn to the same scale.
255/45R21 vs 295/40R21 differences
Measurement255/45R21295/40R21Difference% diff
Overall diameter30.04 in (762.9 mm)30.29 in (769.4 mm)+0.26 in (+6.5 mm)+0.85%
Sidewall height4.52 in (114.8 mm)4.65 in (118.0 mm)+0.13 in (+3.3 mm)+2.83%
Section width10.04 in (255.0 mm)11.61 in (295.0 mm)+1.57 in (+40.0 mm)+15.69%
Circumference94.36 in (2,396.7 mm)95.16 in (2,417.1 mm)+0.80 in (+20.4 mm)+0.85%
Revolutions per mile671666−6−0.84%
True speed with the speedometer calibrated for 255/45R21
IndicatedActual on 255/45R21Actual on 295/40R21Difference
30 mph30.0 mph30.3 mph+0.3 mph
60 mph60.0 mph60.5 mph+0.5 mph
75 mph75.0 mph75.6 mph+0.6 mph

Ride-height change: 295/40R21 raises the vehicle by 0.13 in (3.3 mm) at the axle (half the +6.5 mm diameter difference).

295/40R21 is 0.26 in taller than 255/45R21 and 40 mm wider, a 0.85% difference in overall diameter.

With the speedometer calibrated for 255/45R21, an indicated 60 mph is actually 60.5 mph on 295/40R21, and revolutions per mile change from 671 to 666.

Both sizes mount on 21-inch wheels.

Size pages

Other comparisons with 255/45R21

Other comparisons with 295/40R21

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