I hate to say it but I would consider this a poor explanation. 1. The explanation on the offset(with the first picture) doesn't make reference to the important detail called the centerline of the wheel. Only the first line when they point out what "ZERO OFFSET" is. When talking about positive and negative, they should make it clear that it's relative to the distance of the hub to the "centerline" of the wheel. For example... POSITIVE The hub mounting surface is toward the front or “wheel side” of the wheel(street side) relative to the centerline of the wheel. Positive offset wheels are generally found on front wheel drive cars and newer rear drive cars. An example of a positive offset wheel is the Polaris RZR 1000 which comes stock with a +38mm offset. Higher offsets restrict design and leave the wheel looking flat, with little to no depth in spoke design/lip. NEGATIVE The hub mounting surface is toward the back or brake side of the wheel, relative to the centerline of the wheel.. “Deep dish” wheels are typically a negative offset and benefit the design process by allowing sharp angles, deep spokes and incredible layering. In the 2nd set of pictures entitled, Need a visual? Check this out: it does an extremely poor job of actually pointing out the positive and negative offsets. The 1st picture comes close to pointing it out but falls short. What are they conveying by showing this info below the wheels??? I know what their trying to do but I think it is very confusing. They don't menton the fact the the 7" wheel dimension is to the inside rims and not to the outer edge of the rims where the backspace is actually measured from. And I'm still trying to figure out the purpose of "-47mm conversion = 1.65+5.35". I guess that's suppose to help you understand the calculation they show you above. Which in itself is screwed up. They say to calculate you need... Wheel backspace (see above) Wheel width Wheel centerline (outboard flange to inboard flange measurement, divided by 2) ONCE YOU HAVE THESE MEASUREMENTS, YOU NEED TO SUBTRACT THE WHEEL CENTERLINE FROM WHEEL BACKSPACE TO GET THE OFFSET. But their not using the wheel width in their method which is 7". They are using the overall width of the wheel including the 2 rims. "outboard flange to inboard flange measurement, divided by 2)" Yeah I have nothing better to do with my time. I'll find something a little better and if someone wants to figure the offset by using the backspace(or vice versa) they can use this chart.
Can't find some of the better explanations I've seen for offsets and back space but rather then calculate and/or measure it, I would suggest looking at the back side of your wheel for the imprinted offset value. As shown on my wheel above, it's a 20 dia x 9.5" wide with a +18.5mm offset. The offset is sometime identified with an "E.T." prefix. In the absence of a + or - signs, it would be a positive. It may appear on a different part of the wheel, such as on back of one of the spokes, or not at all.
Here are a few pictures showing some common fitment terms and measurements. So in other words, decreasing the amount of offset would move the wheel outward , away from the suspension and increasing would move it in towards the suspension. The Pilot Diameter, shown above, is referred to as the Center Bore Diameter and in the case of the Challengers is typically 71.5mm. It should also be noted that the caliper height varies based on type of brakes. The wheel manufacturer should be consulted relative to their wheel being capable of clearing a particular brake assembly. It should also be noted that it's the spoke design and placement that determines this clearance and not the backspace or offset.
