Wheel Experts, help me figure this out.

Since my wheel guy is MIA (looking at you mndsm ), I am in a argument with a couple Corvair guys over wheel offset and backspacing. I feel like they are wrong, but maybe I am.

To my understanding, wheel offset is zero, positive, or negative. The following is in reference from going from an OEM wheel (-1" offset) to an aftermarket one (zero offset). Both wheels are the same width.

Zero Offset is where the mounting surface (where it contacts the rotor/drum) of hub is in the centerline of the wheel.

Positive offset makes the hub move towards the outside of the rim, creating more backspace and making the inside of the rim closer to the suspension.

Negative offset makes the hub move towards the inside of the rim, creating less backspace and making the outside of the rim closer to the lip of the wheel well.

This is what one of the guys is telling me:

"Zero" offset means the wheel is centered in/out relative to the hub. The stock wheels are 1" inboard - toward the suspension - from that measurement. So zero offset wheels are moved out 1" from the factory spec. Using backspace, zero offset wheels have less backspace than stock, so toward the fender edge.

So he is telling me the opposite of what I know and the wheel guide I've been using is wrong.

This is from the wheel guide that I use with the OPs wheel info, OEM wheel on the left, new wheel on the right:

So am I wrong? Because if I am, I'm glad I haven't bought any wheels yet.

You are correct. He seems mixed up more than anything else, as he's on the right train of thought but his language is a little unclear.

The stock wheels are 1" inboard - toward the suspension - from that measurement. So zero offset wheels are moved out 1" from the factory spec.

It almost sounds like he is mixing up backspacing and offset from these two sentences.

The stock wheels have 1in of POSITIVE offset based on what he's saying. Zero offset will move outwards(stick out more).

He's got positive and negative backwards. And/or is thinking in terms of backspace, where less of it moves wheels outwards.

Generally speaking, positive offset has higher backspacing. Now.

It wasn't always this way, and you might get different answers depending on who you talked to. Maybe your Corvair friends are remembering from back-inna-day from companies that defined positive offset as lower backspacing.

Interesting read: http://bacomatic.org/~dw/library/txt/offset.htm The offset thing bugged me too when I got Puhn's book. But then it always bugs me when I buy a "Definitive Source" and it contains info that I know is wrong. It throws the rest of the info into question. (And don't GET me started on a certain book about forced induction. I keep it mainly for the humor value)

This is why I really, really prefer backspacing as a wheel metric. Of course, backspacing includes the wheel lip, which is not counted as part of the rim width, so a direct formula to convert from one to the other isn't generally possible.

So the guy who I posted about, has a page for Corvair owners about finding wheels. I comprehend it, but it is all over the board and it does get confusing, especially to someone who doesn't know wheels. I hate when Corvair folks just share the page, because I feel that it doesn't provide enough info for modern wheels, which is what a lot of people are looking for nowadays:

http://autoxer.skiblack.com/tires.html

I'm not trying to make the guy look bad, he is a well revered autocrosser, I just feel like his wheel info is giving people the wrong info.

You are right.

If you have a 6" wide wheel with zero offset, the backspacing will be 3" plus the lip. The wheel width is measured inside the lip where the bead of the tire sits. If you changed to a 7" wide wheel with zero offset, the backspacing will be 3.5" plus the lip. (adds 1/2" inside and outside) To keep the same backspacing you would have to go with a wheel with an offset of -0.5".

Changing wheel widths on the same offset changes backspacing. Changing wheel widths on the same backspacing changes offset.

Offset is the mounting flange's relationship to the centerline of the wheel. Backspacing is the overall distance from the mounting flange to the innermost surface of the wheel.

Sorry man, i was in vero beach not getting stung by man o wars. All of what the others have said is correct. Backspacing and offset are the same thing, just different ways of measuring it. Text me if you have more questions.

So another wheel post came up and it finally came to light why he is always saying opposite what of what I say, is because he refers to offset by what direction the rim goes, not the hub.

So......hes a dummy. Got it.

In reply to mndsm:

I don't know if it so much that, he comes from a time when wheel companies had their own ideas of offset, not like today where it's more standardized.

The replacement wheel will move the tire in towards the suspension.

Back spacing is so much simpler than all the positive, zero, negative crap.

FWD cars have lots of back spacing, most RWD cars have less. QED

Yeah, us Corvair guys are all weird.