TireSizesFinder

235/70R17 vs 275/55R18

275/55R18 is 0.04 in (1.1 mm) shorter than 235/70R17, a −0.14% diameter difference. With the speedometer set for 235/70R17, an indicated 60 mph is 59.9 mph on 275/55R18.

Is this a safe swap?

Diameter difference −0.14%: under 1%

By overall diameter alone, 275/55R18 is a near match for 235/70R17; 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: 235/70R17 (29.95 in) vs 275/55R18 (29.91 in)235/70R1729.95 in × 9.25 in275/55R1829.91 in × 10.83 in
Side profile and tread width, drawn to the same scale.
235/70R17 vs 275/55R18 differences
Measurement235/70R17275/55R18Difference% diff
Overall diameter29.95 in (760.8 mm)29.91 in (759.7 mm)−0.04 in (−1.1 mm)−0.14%
Sidewall height6.48 in (164.5 mm)5.95 in (151.3 mm)−0.52 in (−13.2 mm)−8.05%
Section width9.25 in (235.0 mm)10.83 in (275.0 mm)+1.57 in (+40.0 mm)+17.02%
Circumference94.10 in (2,390.1 mm)93.96 in (2,386.7 mm)−0.14 in (−3.5 mm)−0.14%
Revolutions per mile673674+1+0.14%
True speed with the speedometer calibrated for 235/70R17
IndicatedActual on 235/70R17Actual on 275/55R18Difference
30 mph30.0 mph30.0 mph0.0 mph
60 mph60.0 mph59.9 mph−0.1 mph
75 mph75.0 mph74.9 mph−0.1 mph

Ride-height change: 275/55R18 lowers the vehicle by 0.02 in (0.5 mm) at the axle (half the −1.1 mm diameter difference).

275/55R18 is 0.04 in shorter than 235/70R17 and 40 mm wider, a 0.14% difference in overall diameter.

With the speedometer calibrated for 235/70R17, an indicated 60 mph is actually 59.9 mph on 275/55R18, and revolutions per mile change from 673 to 674.

275/55R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 235/70R17.

Size pages

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