Use a comparison tool from the web and you can see the exact difference
Stock Tire - 315/70R17 >Search Tires Tire 1 - 325/60R20 >Search Tires Section Width:12.40 in315 mmSection Width:12.79 in325 mmRim Diameter:17 in431.8 mmRim Diameter:20 in508 mmRim Width Range:8.5 - 10 inRim Width Range:9 - 10 inOverall Diameter:34.36 in872.74 mmOverall Diameter:35.35 in897.89 mmSidewall Height:8.68 in220.47 mmSidewall Height:7.67 in194.81 mmRadius:17.18 in436.37 mmRadius:17.67 in448.81 mmCircumference:107.9 in2740.6 mmCircumference:111.0 in2819.4 mmRevs per Mile:605.3Revs per Mile:588.4Actual Speed:60 mph100 km/hSpeedometer1:58.3 mph97.2 km/hSpeedometer Difference: -Speedometer Difference: 2.872% too slowDiameter Difference: -
Diameter Difference: 2.81%
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