TireSizesFinder

315/70R18 vs 325/60R20

325/60R20 is 0.01 in (0.2 mm) shorter than 315/70R18, a −0.02% diameter difference. With the speedometer set for 315/70R18, an indicated 60 mph is 60.0 mph on 325/60R20.

Is this a safe swap?

Diameter difference −0.02%: under 1%

By overall diameter alone, 325/60R20 is a near match for 315/70R18; 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: 315/70R18 (35.36 in) vs 325/60R20 (35.35 in)315/70R1835.36 in × 12.40 in325/60R2035.35 in × 12.80 in
Side profile and tread width, drawn to the same scale.
315/70R18 vs 325/60R20 differences
Measurement315/70R18325/60R20Difference% diff
Overall diameter35.36 in (898.2 mm)35.35 in (898.0 mm)−0.01 in (−0.2 mm)−0.02%
Sidewall height8.68 in (220.5 mm)7.68 in (195.0 mm)−1.00 in (−25.5 mm)−11.56%
Section width12.40 in (315.0 mm)12.80 in (325.0 mm)+0.39 in (+10.0 mm)+3.17%
Circumference111.09 in (2,821.8 mm)111.07 in (2,821.2 mm)−0.02 in (−0.6 mm)−0.02%
Revolutions per mile5705700+0.02%
True speed with the speedometer calibrated for 315/70R18
IndicatedActual on 315/70R18Actual on 325/60R20Difference
30 mph30.0 mph30.0 mph0.0 mph
60 mph60.0 mph60.0 mph0.0 mph
75 mph75.0 mph75.0 mph0.0 mph

Ride-height change: 325/60R20 lowers the vehicle by 0.00 in (0.1 mm) at the axle (half the −0.2 mm diameter difference).

325/60R20 is 0.01 in shorter than 315/70R18 and 10 mm wider, a 0.02% difference in overall diameter.

With the speedometer calibrated for 315/70R18, an indicated 60 mph is actually 60.0 mph on 325/60R20, and revolutions per mile change from 570 to 570.

325/60R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 315/70R18.

Size pages

Other comparisons with 315/70R18

Other comparisons with 325/60R20

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