Don't understand what is being explained to you by your local tire tech, or for that matter, even us?!? The following is a basic guide that points out some of the more commonly used terminology, and should better help you to understand the complexities that are involved in something as simple as a wheel.
Bolt patterns are fairly simple concepts. Your first number in the bolt pattern will always be the number of studs on the vehicle. for example, the first image in the picture above is a 4 lug. Your second number, will be the spread as measured above. This number can me either metric or standard. For the first image, if the spread or distance between the two were 100mm, then our bolt pattern on that vehicle would be stated as 4x100. The same process carries to all vehicles.
The easiest way to measure backspace is to lay the wheel face down
onto the ground so the backside of the wheel is facing up. Take a
straight edge and lay it diagonally across the inboard flange of the
wheel. Take a tape measure and measure the distance from where the
straight edge contacts the inboard flange to the hub mounting pad
of the wheel. This measurement is backspace. The above photo shows
three wheels with 2",3", & 4" backspace.
To calculate offset you'll need the following measurements:
::: Wheel backspace
::: Wheel Width
::: Wheel Center line (wheel width / 2)
Subtract:
Wheel center line from Wheel backspace to get offset. If backspace is less than the wheel centerline the offset is negative
If backspace is greater than the wheel centerline the offset is positive.
Tip:
::: To convert from inches to mm multiply by 25.4
::: To convert from mm to inches divide by 25.4
3100DD Wheels
