TireSizesFinder

225/40R19 vs 255/30R20

255/30R20 is 0.06 in (1.6 mm) shorter than 225/40R19, a −0.24% diameter difference. With the speedometer set for 225/40R19, an indicated 60 mph is 59.9 mph on 255/30R20.

Is this a safe swap?

Diameter difference −0.24%: under 1%

By overall diameter alone, 255/30R20 is a near match for 225/40R19; 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: 225/40R19 (26.09 in) vs 255/30R20 (26.02 in)225/40R1926.09 in × 8.86 in255/30R2026.02 in × 10.04 in
Side profile and tread width, drawn to the same scale.
225/40R19 vs 255/30R20 differences
Measurement225/40R19255/30R20Difference% diff
Overall diameter26.09 in (662.6 mm)26.02 in (661.0 mm)−0.06 in (−1.6 mm)−0.24%
Sidewall height3.54 in (90.0 mm)3.01 in (76.5 mm)−0.53 in (−13.5 mm)−15.00%
Section width8.86 in (225.0 mm)10.04 in (255.0 mm)+1.18 in (+30.0 mm)+13.33%
Circumference81.95 in (2,081.6 mm)81.76 in (2,076.6 mm)−0.20 in (−5.0 mm)−0.24%
Revolutions per mile773775+2+0.24%
True speed with the speedometer calibrated for 225/40R19
IndicatedActual on 225/40R19Actual on 255/30R20Difference
30 mph30.0 mph29.9 mph−0.1 mph
60 mph60.0 mph59.9 mph−0.1 mph
75 mph75.0 mph74.8 mph−0.2 mph

Ride-height change: 255/30R20 lowers the vehicle by 0.03 in (0.8 mm) at the axle (half the −1.6 mm diameter difference).

255/30R20 is 0.06 in shorter than 225/40R19 and 30 mm wider, a 0.24% difference in overall diameter.

With the speedometer calibrated for 225/40R19, an indicated 60 mph is actually 59.9 mph on 255/30R20, and revolutions per mile change from 773 to 775.

255/30R20 mounts on a 20-inch wheel, a plus-1 fitment from the 19-inch wheel of 225/40R19.

Size pages

Other comparisons with 225/40R19

Other comparisons with 255/30R20

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