TireSizesFinder

235/50R19 vs 305/30R21

305/30R21 is 0.05 in (1.2 mm) shorter than 235/50R19, a −0.17% diameter difference. With the speedometer set for 235/50R19, an indicated 60 mph is 59.9 mph on 305/30R21.

Is this a safe swap?

Diameter difference −0.17%: under 1%

By overall diameter alone, 305/30R21 is a near match for 235/50R19; 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: 235/50R19 (28.25 in) vs 305/30R21 (28.20 in)235/50R1928.25 in × 9.25 in305/30R2128.20 in × 12.01 in
Side profile and tread width, drawn to the same scale.
235/50R19 vs 305/30R21 differences
Measurement235/50R19305/30R21Difference% diff
Overall diameter28.25 in (717.6 mm)28.20 in (716.4 mm)−0.05 in (−1.2 mm)−0.17%
Sidewall height4.63 in (117.5 mm)3.60 in (91.5 mm)−1.02 in (−26.0 mm)−22.13%
Section width9.25 in (235.0 mm)12.01 in (305.0 mm)+2.76 in (+70.0 mm)+29.79%
Circumference88.76 in (2,254.4 mm)88.61 in (2,250.6 mm)−0.15 in (−3.8 mm)−0.17%
Revolutions per mile714715+1+0.17%
True speed with the speedometer calibrated for 235/50R19
IndicatedActual on 235/50R19Actual on 305/30R21Difference
30 mph30.0 mph29.9 mph−0.1 mph
60 mph60.0 mph59.9 mph−0.1 mph
75 mph75.0 mph74.9 mph−0.1 mph

Ride-height change: 305/30R21 lowers the vehicle by 0.02 in (0.6 mm) at the axle (half the −1.2 mm diameter difference).

305/30R21 is 0.05 in shorter than 235/50R19 and 70 mm wider, a 0.17% difference in overall diameter.

With the speedometer calibrated for 235/50R19, an indicated 60 mph is actually 59.9 mph on 305/30R21, and revolutions per mile change from 714 to 715.

305/30R21 mounts on a 21-inch wheel, a plus-2 fitment from the 19-inch wheel of 235/50R19.

Size pages

Other comparisons with 235/50R19

Other comparisons with 305/30R21

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