TireSizesFinder

255/40R19 vs 245/35R20

245/35R20 is 0.28 in (7.1 mm) shorter than 255/40R19, a −1.03% diameter difference. With the speedometer set for 255/40R19, an indicated 60 mph is 59.4 mph on 245/35R20.

Is this a safe swap?

Diameter difference −1.03%: within the ±3% guideline

By overall diameter alone, 245/35R20 falls inside the ±3% range commonly used as a guideline when replacing 255/40R19. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

To-scale drawing: 255/40R19 (27.03 in) vs 245/35R20 (26.75 in)255/40R1927.03 in × 10.04 in245/35R2026.75 in × 9.65 in
Side profile and tread width, drawn to the same scale.
255/40R19 vs 245/35R20 differences
Measurement255/40R19245/35R20Difference% diff
Overall diameter27.03 in (686.6 mm)26.75 in (679.5 mm)−0.28 in (−7.1 mm)−1.03%
Sidewall height4.02 in (102.0 mm)3.38 in (85.8 mm)−0.64 in (−16.2 mm)−15.93%
Section width10.04 in (255.0 mm)9.65 in (245.0 mm)−0.39 in (−10.0 mm)−3.92%
Circumference84.92 in (2,157.0 mm)84.04 in (2,134.7 mm)−0.88 in (−22.3 mm)−1.03%
Revolutions per mile746754+8+1.04%
True speed with the speedometer calibrated for 255/40R19
IndicatedActual on 255/40R19Actual on 245/35R20Difference
30 mph30.0 mph29.7 mph−0.3 mph
60 mph60.0 mph59.4 mph−0.6 mph
75 mph75.0 mph74.2 mph−0.8 mph

Ride-height change: 245/35R20 lowers the vehicle by 0.14 in (3.5 mm) at the axle (half the −7.1 mm diameter difference).

245/35R20 is 0.28 in shorter than 255/40R19 and 10 mm narrower, a 1.03% difference in overall diameter.

With the speedometer calibrated for 255/40R19, an indicated 60 mph is actually 59.4 mph on 245/35R20, and revolutions per mile change from 746 to 754.

245/35R20 mounts on a 20-inch wheel, a plus-1 fitment from the 19-inch wheel of 255/40R19.

Size pages

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