TireSizesFinder

305/30R19 vs 275/30R20

275/30R20 is 0.29 in (7.4 mm) taller than 305/30R19, a +1.11% diameter difference. With the speedometer set for 305/30R19, an indicated 60 mph is 60.7 mph on 275/30R20.

Is this a safe swap?

Diameter difference +1.11%: within the ±3% guideline

By overall diameter alone, 275/30R20 falls inside the ±3% range commonly used as a guideline when replacing 305/30R19. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

To-scale drawing: 305/30R19 (26.20 in) vs 275/30R20 (26.50 in)305/30R1926.20 in × 12.01 in275/30R2026.50 in × 10.83 in
Side profile and tread width, drawn to the same scale.
305/30R19 vs 275/30R20 differences
Measurement305/30R19275/30R20Difference% diff
Overall diameter26.20 in (665.6 mm)26.50 in (673.0 mm)+0.29 in (+7.4 mm)+1.11%
Sidewall height3.60 in (91.5 mm)3.25 in (82.5 mm)−0.35 in (−9.0 mm)−9.84%
Section width12.01 in (305.0 mm)10.83 in (275.0 mm)−1.18 in (−30.0 mm)−9.84%
Circumference82.32 in (2,091.0 mm)83.24 in (2,114.3 mm)+0.92 in (+23.2 mm)+1.11%
Revolutions per mile770761−8−1.10%
True speed with the speedometer calibrated for 305/30R19
IndicatedActual on 305/30R19Actual on 275/30R20Difference
30 mph30.0 mph30.3 mph+0.3 mph
60 mph60.0 mph60.7 mph+0.7 mph
75 mph75.0 mph75.8 mph+0.8 mph

Ride-height change: 275/30R20 raises the vehicle by 0.15 in (3.7 mm) at the axle (half the +7.4 mm diameter difference).

275/30R20 is 0.29 in taller than 305/30R19 and 30 mm narrower, a 1.11% difference in overall diameter.

With the speedometer calibrated for 305/30R19, an indicated 60 mph is actually 60.7 mph on 275/30R20, and revolutions per mile change from 770 to 761.

275/30R20 mounts on a 20-inch wheel, a plus-1 fitment from the 19-inch wheel of 305/30R19.

Size pages

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