THE DIFFERENCE BETWEEN BACKSPACING AND OFFSET
Some of the most frequently asked questions we receive are regarding backspacing and offset. What's the difference between backspacing and offset? What IS backspacing and offset? Continue reading and hopefully, these questions will be answered!
Essentially, without getting too technical, there are three fundamental measurements to a wheel that dictate how it sits within your vehicle's fender wells. Width, Diameter, and Offset/Backspacing. Additional to this, there are other measurements such as the "X-Factor" that is indicative of caliper clearance within a wheel, but that's a discussion for a different day. Now, being in the market for wheels, hopefully, diameter and width aren't too foreign of a concept. Backspacing or Offset is where it gets a bit more complicated.
The reason backspacing and offset are lumped together in one category, is because they indicate the same information, using different methods. Offset is more commonly used within the import community and is measured in a positive or negative millimeter value. Backspacing is more commonly found in the domestic community, measured in inches, and will always be a positive value. The Diagram below explains further:
As you can see above, all three wheels are the same diameter and width. However, for each of these wheels, where they mount to the hub of your vehicle is in a different position. The wheel on the left will sit substantially further inwards on your vehicle than the wheel on the right, even though they are the same width. This is why offset and backspacing is an important measurement to make note of when purchasing.
Now for the difference between Backspacing and Offset. Backspacing is measured from the backplane of the wheel to the hub face of the wheel. Offset is measured from the middle of the wheel, to where the hub face is located, which can either be a positive or negative value. Negative making the wheel sit further out, Positive making the wheel sit further in. Let's take the middle wheel of the diagram, and say it's measurement is as follows:
+ indicates this is an offset measurement, not a backspacing measurement. Offset is also sometimes indicated as ET. The 0 measurement indicates that the hub face of the wheel mounts dead center, in terms of the width of the wheel. The same wheel measured using backspacing would be as such:
16x8, 4-inch backspace
Because 4 inches is exactly half of 8, and +0 indicates mounting exactly at the centerline, these two wheels will fit the same.
Hopefully, this helps those that are a bit confused. For further questions do not hesitate to shoot us an email! -Derrick Cui of Summit Offroad Wheels