TireSizesFinder

295/35R18 vs 255/30R20

255/30R20 is 0.11 in (2.7 mm) shorter than 295/35R18, a −0.41% diameter difference. With the speedometer set for 295/35R18, an indicated 60 mph is 59.8 mph on 255/30R20.

Is this a safe swap?

Diameter difference −0.41%: under 1%

By overall diameter alone, 255/30R20 is a near match for 295/35R18; 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: 295/35R18 (26.13 in) vs 255/30R20 (26.02 in)295/35R1826.13 in × 11.61 in255/30R2026.02 in × 10.04 in
Side profile and tread width, drawn to the same scale.
295/35R18 vs 255/30R20 differences
Measurement295/35R18255/30R20Difference% diff
Overall diameter26.13 in (663.7 mm)26.02 in (661.0 mm)−0.11 in (−2.7 mm)−0.41%
Sidewall height4.06 in (103.3 mm)3.01 in (76.5 mm)−1.05 in (−26.7 mm)−25.91%
Section width11.61 in (295.0 mm)10.04 in (255.0 mm)−1.57 in (−40.0 mm)−13.56%
Circumference82.09 in (2,085.1 mm)81.76 in (2,076.6 mm)−0.33 in (−8.5 mm)−0.41%
Revolutions per mile772775+3+0.41%
True speed with the speedometer calibrated for 295/35R18
IndicatedActual on 295/35R18Actual on 255/30R20Difference
30 mph30.0 mph29.9 mph−0.1 mph
60 mph60.0 mph59.8 mph−0.2 mph
75 mph75.0 mph74.7 mph−0.3 mph

Ride-height change: 255/30R20 lowers the vehicle by 0.05 in (1.4 mm) at the axle (half the −2.7 mm diameter difference).

255/30R20 is 0.11 in shorter than 295/35R18 and 40 mm narrower, a 0.41% difference in overall diameter.

With the speedometer calibrated for 295/35R18, an indicated 60 mph is actually 59.8 mph on 255/30R20, and revolutions per mile change from 772 to 775.

255/30R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 295/35R18.

Size pages

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