TireSizesFinder

275/35R18 vs 225/30R20

225/30R20 is 0.26 in (6.7 mm) shorter than 275/35R18, a −1.03% diameter difference. With the speedometer set for 275/35R18, an indicated 60 mph is 59.4 mph on 225/30R20.

Is this a safe swap?

Diameter difference −1.03%: within the ±3% guideline

By overall diameter alone, 225/30R20 falls inside the ±3% range commonly used as a guideline when replacing 275/35R18. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

To-scale drawing: 275/35R18 (25.58 in) vs 225/30R20 (25.31 in)275/35R1825.58 in × 10.83 in225/30R2025.31 in × 8.86 in
Side profile and tread width, drawn to the same scale.
275/35R18 vs 225/30R20 differences
Measurement275/35R18225/30R20Difference% diff
Overall diameter25.58 in (649.7 mm)25.31 in (643.0 mm)−0.26 in (−6.7 mm)−1.03%
Sidewall height3.79 in (96.3 mm)2.66 in (67.5 mm)−1.13 in (−28.7 mm)−29.87%
Section width10.83 in (275.0 mm)8.86 in (225.0 mm)−1.97 in (−50.0 mm)−18.18%
Circumference80.36 in (2,041.1 mm)79.53 in (2,020.0 mm)−0.83 in (−21.0 mm)−1.03%
Revolutions per mile788797+8+1.04%
True speed with the speedometer calibrated for 275/35R18
IndicatedActual on 275/35R18Actual on 225/30R20Difference
30 mph30.0 mph29.7 mph−0.3 mph
60 mph60.0 mph59.4 mph−0.6 mph
75 mph75.0 mph74.2 mph−0.8 mph

Ride-height change: 225/30R20 lowers the vehicle by 0.13 in (3.4 mm) at the axle (half the −6.7 mm diameter difference).

225/30R20 is 0.26 in shorter than 275/35R18 and 50 mm narrower, a 1.03% difference in overall diameter.

With the speedometer calibrated for 275/35R18, an indicated 60 mph is actually 59.4 mph on 225/30R20, and revolutions per mile change from 788 to 797.

225/30R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 275/35R18.

Size pages

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