Wheels for a duster offset and backspace

03JeepJeep said
From what I understand offset measures the distance between the wheel center and the mounting surface and backspace measures the distance between the mounting face and the inside edge of the wheel.

DionR said
It is all related to the mounting surface of the wheel.

"Backspacing is defined as the distance from the hub mounting surface to the inside lip of the wheel (measured in inches). More backspacing puts the tire in closer to the center of the truck."

Back spacing is a little difficult to calculate because it is between mounting surface of the wheel and the outside of the lip of the wheel, while the wheel width is actually measure from inside to inside of the lip. And because nobody lists the thickness of the lip, I just use 1/2" as an assumption.

The other measurement is offset which relates to how far the mounting surface is from the centerline of the wheel barrel. Positive being away from the centerline of the car and negative towards the centerline of the car.

So, your 7" wide rim with 38mm of positive offset should calculate out to 5.5" backspacing assuming 1/2" for the wheel lip:

3.5" (half the rim width) + 1.50" (offset in inches) + 1/2" (lip thickness) = 5.5"

In the case of a negative offset, subtract the offset rather than add it.

Here's a link to someplace to read about it - https://www.discounttiredirect.com/learn/offset-backspace

Backspace is NOT measured to the inside lip of the wheel. It's measured from the outside of the lip to the mounting pad. Yes, I realize discount tire direct says otherwise, but they've got it wrong.

Forgeline actually makes wheels (really expensive ones at that!), here's their explanation of backspace and offset.

And if that's not good enough for you, here's a few more

https://blog.tirerack.com/blog/turk-t/measuring-backspacing
https://static.summitracing.com/global/images/instructions/crw-35-580547500.pdf
https://www.jegs.com/images/wheelmeasureguide.pdf
Offset Explained | WheelPros

Not sure what they're smoking over at discount tire direct. Maybe they're thinking they'll sell more rims if everyone put their rims a ~1/2" too close to their springs?

Not enough you say? Here's one of the wheels from my Challenger
Vision American Muscle 141 Legend 5 Series Gunmetal Wheels 141H7965GM0

Screen Shot 2016-10-03 at 9.23.33 PM.png

Screen Shot 2016-10-03 at 9.23.33 PM.png

17x9, 0 offset, 5" backspace.

ET 0, 17x9, cast into the rim...

And look at that, outside lip to mounting surface, 5".