The 2006 Chevrolet Cobalt Sedan with 4 Lug Wheels LTZ bolt pattern is 4-100 mm. This means there are 4 lugs and the diameter of the circle that the lugs make up measures 100 mm or 3.94 inches across. To get a close measurement of your 4 lug bolt pattern without a bolt pattern tool you should measure from the center of one lug to the center of the lug across from it.
