TireSizesFinder

285/45R20 vs 235/55R20

235/55R20 is 0.08 in (2.0 mm) taller than 285/45R20, a +0.26% diameter difference. With the speedometer set for 285/45R20, an indicated 60 mph is 60.2 mph on 235/55R20.

Is this a safe swap?

Diameter difference +0.26%: under 1%

By overall diameter alone, 235/55R20 is a near match for 285/45R20; 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: 285/45R20 (30.10 in) vs 235/55R20 (30.18 in)285/45R2030.10 in × 11.22 in235/55R2030.18 in × 9.25 in
Side profile and tread width, drawn to the same scale.
285/45R20 vs 235/55R20 differences
Measurement285/45R20235/55R20Difference% diff
Overall diameter30.10 in (764.5 mm)30.18 in (766.5 mm)+0.08 in (+2.0 mm)+0.26%
Sidewall height5.05 in (128.3 mm)5.09 in (129.3 mm)+0.04 in (+1.0 mm)+0.78%
Section width11.22 in (285.0 mm)9.25 in (235.0 mm)−1.97 in (−50.0 mm)−17.54%
Circumference94.56 in (2,401.7 mm)94.80 in (2,408.0 mm)+0.25 in (+6.3 mm)+0.26%
Revolutions per mile670668−2−0.26%
True speed with the speedometer calibrated for 285/45R20
IndicatedActual on 285/45R20Actual on 235/55R20Difference
30 mph30.0 mph30.1 mph+0.1 mph
60 mph60.0 mph60.2 mph+0.2 mph
75 mph75.0 mph75.2 mph+0.2 mph

Ride-height change: 235/55R20 raises the vehicle by 0.04 in (1.0 mm) at the axle (half the +2.0 mm diameter difference).

235/55R20 is 0.08 in taller than 285/45R20 and 50 mm narrower, a 0.26% difference in overall diameter.

With the speedometer calibrated for 285/45R20, an indicated 60 mph is actually 60.2 mph on 235/55R20, and revolutions per mile change from 670 to 668.

Both sizes mount on 20-inch wheels.

Size pages

Other comparisons with 285/45R20

Other comparisons with 235/55R20

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