Miata Daisy advice

[TominMO]

No problem. It's easy to get confused because "backspacing" works opposite of offset. Backspacing is measured in inches and is the common wheel measurement on domestic vehicles and domestic racing wheels. Backspacing is measured from the outer bead lip of the wheel inward to the hub mount surface. Offset is measured from wheel centerline towards the outer bead lip.
For example.
A 7 inch wide wheel with 3" inches of backspacing is equal to a 7" wide wheel with 1 inch of offset. But, since offset is always measured in mm, the offset would be shown as 25mm (ET25). I run 7 inch wide wheels with 25mm offset on my Festivas, but this requires fender rolling and at least 2.5 degrees negative camber on all 4 corners.

Hmmmm.....need further clarification.

A 7" wheel would have its midpoint at 3.5", right? That midpoint would be 0mm offset. So it seems to me that 3" of backspacing would be 1/2" (12.7mm) outboard from the center, and put the offset at 12.7mm (round up to 13mm).

Or is it that the difference between the outer bead lip and the inner side of the lip is 1/2"? If so, would that explain the difference, and therefore my confusion? IDK if the 7" rim width is measured from outer lip to outer lip, or from the insides of the beads.

[Advancedynamix]

Hmmmm.....need further clarification.

A 7" wheel would have its midpoint at 3.5", right? That midpoint would be 0mm offset. So it seems to me that 3" of backspacing would be 1/2" (12.7mm) outboard from the center, and put the offset at 12.7mm (round up to 13mm).

Or is it that the difference between the outer bead lip and the inner side of the lip is 1/2"? If so, would that explain the difference, and therefore my confusion? IDK if the 7" rim width is measured from outer lip to outer lip, or from the insides of the beads.

Haha, it seems you don't need further clarification Tom. My math was wrong. Your correct 7" rim with 3" backspacing would be a 12.7mm (et13) offset. A 7" wide rim with 3" backspacing will poke out pretty bad on a Festiva unless you run around 4 degrees of negative camber on all 4 wheels.

For example, these wheels are 13x6 with a 15mm offset and they barely fit under my Festiva with 3 degrees of negative camber.

A 7" wide wheel with a 13mm offset would stick out another half inch and that would rub pretty bad.