As you can see, backspace and offset are closely related. As we said before, many manufacturers have done the work for you by using both measurements in their product descriptions. Want to know how to calculate them on your own? Our sidebars will show you how to do just that.
Quick Equations
Here are some crib notes for figuring out backspace, centerline, and offset.* Step 1: Measure the room in your wheel wells relative to the wheel hub.
* Step 2: Backspace = The distance from back of the wheel to the wheel's mounting space, in inches.
* Step 3: Centerline = The wheel width divided by 2, in inches.
* Step 4: Offset = Backspace - Centerline, which will be positive or negative, in inches.
* Step 5: Offset in Millimeters = Offset x 25.4.]
What Is My Wheel's Backspace?To determine the wheel's backspace, lay the wheel flat on the ground with the back facing upward. Next, lay a straightedge across the wheel and measure the distance from the back of the mounting surface to the strait edge. The backspace of the wheel pictured here is 5.25 inches. We calculated the wheel's offset in the quick equations.
What is My Truck's Backspace?You can measure how much space your truck has for wheels by making all your suspension, brake, and fender mods first. Then, simply measure the distance from the wheel hub on the spindle/axle back toward the first obstruction, such as your tie rods, etc. This will give you an idea of how much wheel backspace your truck can handle. Measure from the hub to the fender to find the amount of front space you can handle there, too. Next, we will calculate a wheel's backspace.