TireSizesFinder

235/45R18 vs 225/35R20

225/35R20 is 0.13 in (3.2 mm) shorter than 235/45R18, a −0.48% diameter difference. With the speedometer set for 235/45R18, an indicated 60 mph is 59.7 mph on 225/35R20.

Is this a safe swap?

Diameter difference −0.48%: under 1%

By overall diameter alone, 225/35R20 is a near match for 235/45R18; 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: 235/45R18 (26.33 in) vs 225/35R20 (26.20 in)235/45R1826.33 in × 9.25 in225/35R2026.20 in × 8.86 in
Side profile and tread width, drawn to the same scale.
235/45R18 vs 225/35R20 differences
Measurement235/45R18225/35R20Difference% diff
Overall diameter26.33 in (668.7 mm)26.20 in (665.5 mm)−0.13 in (−3.2 mm)−0.48%
Sidewall height4.16 in (105.8 mm)3.10 in (78.8 mm)−1.06 in (−27.0 mm)−25.53%
Section width9.25 in (235.0 mm)8.86 in (225.0 mm)−0.39 in (−10.0 mm)−4.26%
Circumference82.71 in (2,100.8 mm)82.31 in (2,090.7 mm)−0.40 in (−10.1 mm)−0.48%
Revolutions per mile766770+4+0.48%
True speed with the speedometer calibrated for 235/45R18
IndicatedActual on 235/45R18Actual on 225/35R20Difference
30 mph30.0 mph29.9 mph−0.1 mph
60 mph60.0 mph59.7 mph−0.3 mph
75 mph75.0 mph74.6 mph−0.4 mph

Ride-height change: 225/35R20 lowers the vehicle by 0.06 in (1.6 mm) at the axle (half the −3.2 mm diameter difference).

225/35R20 is 0.13 in shorter than 235/45R18 and 10 mm narrower, a 0.48% difference in overall diameter.

With the speedometer calibrated for 235/45R18, an indicated 60 mph is actually 59.7 mph on 225/35R20, and revolutions per mile change from 766 to 770.

225/35R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 235/45R18.

Size pages

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