I'm thinking of putting either Panasport or Konig Rewinds on my '73. I've seen several sites list the 7" wide versions (both 15 and 16" diameter) as having a 4" backspace and zero offset. I was thinking a little about this and believe that can't be true! Check out the drawing I grabbed from the Yokohama website.

As I understand it, if the back space of a 7" rim is really 4", then the offset would have to be + 0.5" or roughly 12 mm.

Alternatively, if the offset is really zero, then the backspace would have to be 3.5".

Would anyone who has a set mind measuring the backspace? I realize measuring offset isn't as easy

Offset and rim width are both measured based on the rim seating surfaces, which is the spot where the bead of the tire sits. Those are 7" apart, and if the offset is zero, the hub mounting surface is centered between the two bead seats.

The backside is measured differently. It is measured from the hub mounting surface to the inner bead lip. The difference comes from the fact that the bead lips are typically .5" thick. So for example, if you measure a 7" wheel from the outside bead lip to the inside lip, it will have an overall width of 8 inches, not 7.

So a 7" wheel with zero offset, a 4" backside is correct. It just sounds funny.