TireSizesFinder

275/70R17 vs 255/70R18

255/70R18 is 0.10 in (2.6 mm) shorter than 275/70R17, a −0.32% diameter difference. With the speedometer set for 275/70R17, an indicated 60 mph is 59.8 mph on 255/70R18.

Is this a safe swap?

Diameter difference −0.32%: under 1%

By overall diameter alone, 255/70R18 is a near match for 275/70R17; 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: 275/70R17 (32.16 in) vs 255/70R18 (32.06 in)275/70R1732.16 in × 10.83 in255/70R1832.06 in × 10.04 in
Side profile and tread width, drawn to the same scale.
275/70R17 vs 255/70R18 differences
Measurement275/70R17255/70R18Difference% diff
Overall diameter32.16 in (816.8 mm)32.06 in (814.2 mm)−0.10 in (−2.6 mm)−0.32%
Sidewall height7.58 in (192.5 mm)7.03 in (178.5 mm)−0.55 in (−14.0 mm)−7.27%
Section width10.83 in (275.0 mm)10.04 in (255.0 mm)−0.79 in (−20.0 mm)−7.27%
Circumference101.03 in (2,566.1 mm)100.70 in (2,557.9 mm)−0.32 in (−8.2 mm)−0.32%
Revolutions per mile627629+2+0.32%
True speed with the speedometer calibrated for 275/70R17
IndicatedActual on 275/70R17Actual on 255/70R18Difference
30 mph30.0 mph29.9 mph−0.1 mph
60 mph60.0 mph59.8 mph−0.2 mph
75 mph75.0 mph74.8 mph−0.2 mph

Ride-height change: 255/70R18 lowers the vehicle by 0.05 in (1.3 mm) at the axle (half the −2.6 mm diameter difference).

255/70R18 is 0.10 in shorter than 275/70R17 and 20 mm narrower, a 0.32% difference in overall diameter.

With the speedometer calibrated for 275/70R17, an indicated 60 mph is actually 59.8 mph on 255/70R18, and revolutions per mile change from 627 to 629.

255/70R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 275/70R17.

Size pages

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