255/35R19 vs 305/30R19

305/30R19 is 0.18 in (4.5 mm) taller than 255/35R19, a +0.68% diameter difference. With the speedometer set for 255/35R19, an indicated 60 mph is 60.4 mph on 305/30R19.

Is this a safe swap?

Diameter difference +0.68%: under 1%

By overall diameter alone, 305/30R19 is a near match for 255/35R19; 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.

255/35R19 vs 305/30R19 differences
Measurement	255/35R19	305/30R19	Difference	% diff
Overall diameter	26.03 in (661.1 mm)	26.20 in (665.6 mm)	+0.18 in (+4.5 mm)	+0.68%
Sidewall height	3.51 in (89.3 mm)	3.60 in (91.5 mm)	+0.09 in (+2.3 mm)	+2.52%
Section width	10.04 in (255.0 mm)	12.01 in (305.0 mm)	+1.97 in (+50.0 mm)	+19.61%
Circumference	81.77 in (2,076.9 mm)	82.32 in (2,091.0 mm)	+0.56 in (+14.1 mm)	+0.68%
Revolutions per mile	775	770	−5	−0.68%

True speed with the speedometer calibrated for 255/35R19
Indicated	Actual on 255/35R19	Actual on 305/30R19	Difference
30 mph	30.0 mph	30.2 mph	+0.2 mph
60 mph	60.0 mph	60.4 mph	+0.4 mph
75 mph	75.0 mph	75.5 mph	+0.5 mph

Ride-height change: 305/30R19 raises the vehicle by 0.09 in (2.3 mm) at the axle (half the +4.5 mm diameter difference).

305/30R19 is 0.18 in taller than 255/35R19 and 50 mm wider, a 0.68% difference in overall diameter.

With the speedometer calibrated for 255/35R19, an indicated 60 mph is actually 60.4 mph on 305/30R19, and revolutions per mile change from 775 to 770.

Both sizes mount on 19-inch wheels.

Size pages

Other comparisons with 255/35R19

Other comparisons with 305/30R19

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