Deciding to put a larger diameter or width tire then stock on your Corvette can run you into some unforeseen problems. These problems have to do with the backspacing and offset of the rims and not so much a problem with bolt pattern. So, here at CorvetteGuys we have made a Wheel Tech Guide so that you can understand these terms better and make a better decision when choosing the size of rims for you Corvette
Understanding Corvette Wheels
Offset is probably one of the most confusing aspects of purchasing aftermarket wheels. This shouldn’t be the case since the concept of offset is quite simple. Every wheel has a centerline that divides the wheel’s width into two. The distance from this centerline to where the actual mounting surface is, is what is considered offset. With this being said there are three types of offsets available for any wheel.
Zero Offset – The mounting surface of the wheel is on the centerline of the rim.
Negative Offset – The mounting surface of the wheel is moved in towards the brakes from the centerline.
Positive Offset – The mounting surface of the wheel is moved out towards the street from the centerline.
Backspacing is a direct result of the offset and width of the rim. In general backspacing is the depth from the back of the rim to the mounting surface. This is important to allow room for the brake system and axles to fit behind the wheel. The way to measure the backspacing of a rim is to run a straight edge across the back of your rim and then drop another straight edge down to the center of the rim and that distance is the back spacing.
The bolt pattern is the diameter of the circle of bolts that keep your rim attached to the axle of your Corvette. Since Corvettes come with a 5 lug axle their bolt pattern would read as 5 x 4.75 or 5 x 120, the proper way to read this is the 5 stands for the number of bolts required. In the first example of 5 x 4.75 is measured in inches while the 5 x 120 is measured in millimeters, these are both the same size bolt pattern but represented in different systems of measurement.
The proper way to measure a 5 lug wheel for bolt pattern is to run a straight edge from the center of one lug nut directly across the rim and also have a straight edge along the bottom of the two bolts opposite, this second straight edge will mark where the bolt pattern circle would be. Now simply read the measurement of the first straight edge from the center of the first lug nut to the intersecting point with the other straight edge. This method is used for all odd numbered lug nut wheels, for even numbered lug nut wheels simply run a straight edge from the center of one lug nut to the lug nut directly across and the bolt pattern is determined.