235/40R19 vs 265/30R20

265/30R20 is 0.14 in (3.6 mm) shorter than 235/40R19, a −0.54% diameter difference. With the speedometer set for 235/40R19, an indicated 60 mph is 59.7 mph on 265/30R20.

Is this a safe swap?

Diameter difference −0.54%: under 1%

By overall diameter alone, 265/30R20 is a near match for 235/40R19; the speedometer changes by less than 1%. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

Side profile and tread width, drawn to the same scale.

235/40R19 vs 265/30R20 differences
Measurement	235/40R19	265/30R20	Difference	% diff
Overall diameter	26.40 in (670.6 mm)	26.26 in (667.0 mm)	−0.14 in (−3.6 mm)	−0.54%
Sidewall height	3.70 in (94.0 mm)	3.13 in (79.5 mm)	−0.57 in (−14.5 mm)	−15.43%
Section width	9.25 in (235.0 mm)	10.43 in (265.0 mm)	+1.18 in (+30.0 mm)	+12.77%
Circumference	82.94 in (2,106.8 mm)	82.50 in (2,095.4 mm)	−0.45 in (−11.3 mm)	−0.54%
Revolutions per mile	764	768	+4	+0.54%

True speed with the speedometer calibrated for 235/40R19
Indicated	Actual on 235/40R19	Actual on 265/30R20	Difference
30 mph	30.0 mph	29.8 mph	−0.2 mph
60 mph	60.0 mph	59.7 mph	−0.3 mph
75 mph	75.0 mph	74.6 mph	−0.4 mph

Ride-height change: 265/30R20 lowers the vehicle by 0.07 in (1.8 mm) at the axle (half the −3.6 mm diameter difference).

265/30R20 is 0.14 in shorter than 235/40R19 and 30 mm wider, a 0.54% difference in overall diameter.

With the speedometer calibrated for 235/40R19, an indicated 60 mph is actually 59.7 mph on 265/30R20, and revolutions per mile change from 764 to 768.

265/30R20 mounts on a 20-inch wheel, a plus-1 fitment from the 19-inch wheel of 235/40R19.

Size pages

Other comparisons with 235/40R19

Other comparisons with 265/30R20

Source: Calculated from standard tire geometry formulas. Verified 2026-09-27. How these numbers are calculated.