TireSizesFinder

275/40R18 vs 235/35R20

235/35R20 is 0.19 in (4.7 mm) shorter than 275/40R18, a −0.69% diameter difference. With the speedometer set for 275/40R18, an indicated 60 mph is 59.6 mph on 235/35R20.

Is this a safe swap?

Diameter difference −0.69%: under 1%

By overall diameter alone, 235/35R20 is a near match for 275/40R18; 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: 275/40R18 (26.66 in) vs 235/35R20 (26.48 in)275/40R1826.66 in × 10.83 in235/35R2026.48 in × 9.25 in
Side profile and tread width, drawn to the same scale.
275/40R18 vs 235/35R20 differences
Measurement275/40R18235/35R20Difference% diff
Overall diameter26.66 in (677.2 mm)26.48 in (672.5 mm)−0.19 in (−4.7 mm)−0.69%
Sidewall height4.33 in (110.0 mm)3.24 in (82.3 mm)−1.09 in (−27.7 mm)−25.23%
Section width10.83 in (275.0 mm)9.25 in (235.0 mm)−1.57 in (−40.0 mm)−14.55%
Circumference83.76 in (2,127.5 mm)83.18 in (2,112.7 mm)−0.58 in (−14.8 mm)−0.69%
Revolutions per mile756762+5+0.70%
True speed with the speedometer calibrated for 275/40R18
IndicatedActual on 275/40R18Actual on 235/35R20Difference
30 mph30.0 mph29.8 mph−0.2 mph
60 mph60.0 mph59.6 mph−0.4 mph
75 mph75.0 mph74.5 mph−0.5 mph

Ride-height change: 235/35R20 lowers the vehicle by 0.09 in (2.4 mm) at the axle (half the −4.7 mm diameter difference).

235/35R20 is 0.19 in shorter than 275/40R18 and 40 mm narrower, a 0.69% difference in overall diameter.

With the speedometer calibrated for 275/40R18, an indicated 60 mph is actually 59.6 mph on 235/35R20, and revolutions per mile change from 756 to 762.

235/35R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 275/40R18.

Size pages

Other comparisons with 275/40R18

Other comparisons with 235/35R20

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