The 2011 Ram Dakota Big Horn 2wd Crew Cab bolt pattern is 5-139.7 mm. This means there are 5 lugs and the diameter of the circle that the lugs make up measures 139.7 mm or 5.5 inches across. To get a close measurement of your 5 lug bolt pattern without a bolt pattern tool you should measure from the center of one lug to the outer edge of the lug furthest from it.
