The right tire size for a Pontiac G6 depends on the year of the car and the rim size. For instance, a 2008 Pontiac G6 with 16-inch rims has a tire size of P215/60R16 94S.
The size of a tire is best understood by breaking it down into parts. For instance, the P in the size P215/60R16 94S means it is for a passenger vehicle. The number 215 shows that the width of the tire is 215 millimeters, and the 60 means the tire has an aspect ratio of 60 percent. The R shows that this is a radial tire, and the 16 means it is a 16-inch rim. The 94 represents the load index, and the S indicates the speed rating, which, in this case, is 112 miles per hour.