TireSizesFinder

295/40R18 vs 255/35R20

255/35R20 is 0.26 in (6.7 mm) shorter than 295/40R18, a −0.97% diameter difference. With the speedometer set for 295/40R18, an indicated 60 mph is 59.4 mph on 255/35R20.

Is this a safe swap?

Diameter difference −0.97%: under 1%

By overall diameter alone, 255/35R20 is a near match for 295/40R18; 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: 295/40R18 (27.29 in) vs 255/35R20 (27.03 in)295/40R1827.29 in × 11.61 in255/35R2027.03 in × 10.04 in
Side profile and tread width, drawn to the same scale.
295/40R18 vs 255/35R20 differences
Measurement295/40R18255/35R20Difference% diff
Overall diameter27.29 in (693.2 mm)27.03 in (686.5 mm)−0.26 in (−6.7 mm)−0.97%
Sidewall height4.65 in (118.0 mm)3.51 in (89.3 mm)−1.13 in (−28.7 mm)−24.36%
Section width11.61 in (295.0 mm)10.04 in (255.0 mm)−1.57 in (−40.0 mm)−13.56%
Circumference85.74 in (2,177.8 mm)84.91 in (2,156.7 mm)−0.83 in (−21.0 mm)−0.97%
Revolutions per mile739746+7+0.98%
True speed with the speedometer calibrated for 295/40R18
IndicatedActual on 295/40R18Actual on 255/35R20Difference
30 mph30.0 mph29.7 mph−0.3 mph
60 mph60.0 mph59.4 mph−0.6 mph
75 mph75.0 mph74.3 mph−0.7 mph

Ride-height change: 255/35R20 lowers the vehicle by 0.13 in (3.4 mm) at the axle (half the −6.7 mm diameter difference).

255/35R20 is 0.26 in shorter than 295/40R18 and 40 mm narrower, a 0.97% difference in overall diameter.

With the speedometer calibrated for 295/40R18, an indicated 60 mph is actually 59.4 mph on 255/35R20, and revolutions per mile change from 739 to 746.

255/35R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 295/40R18.

Size pages

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