Wheel Size / Clearance Issues?

[CV355]

I've never heard of negative or positive backspacing, the measurement I'm familiar with is the distance from the wheel mounting surface to the inside of the wheel.  Put the wheel upside down on the ground, lay a straightedge across the back of the wheel, and measure down from the straightedge to the wheel flange mounting surface.  That is the backspacing dimension that is generally published.

That's what I've always figured and been taught.  Thank you!

[Falcon67]

This is going to sound ignorant, but we are talking about negative backspacing, correct? 

Some of the websites I'm looking at do not specify negative/positive backspacing and the wheels I'm looking at (VN427) are custom, no returns

I believe the correct term is + or - "offset", not "backsapce".  Meaning where the axle mounting surface lands vs the centerline of the wheel.

[Heo]

On  steel wheels there is somrtimes stamped a ET Nr
for exampel ET 35 that tell you the  mounting
flange is spaced 35 mm outward of the  center
of the wheel

[TomP]

Yes, that example would be a huge offset like front wheel drive cars and new cars use.
 A common offset for our type of old cars would be ET or +5 to maybe +15.
 The typical old aftermarket wide deep dish wheels would be -20 to -50 or more. Very few had close to zero offset.

 Backspace is not the same thing, offset will vary with wheel width if backspace stays the same. For instance an 8" wide wheel with 5" backspace is likely to fit a stock wheelwell, a 10" wheel with 5" backspace will hang out and a 6" wheel with 5" backspace will have the tire against the inner wheelwell or spring with lots of room outboard.