Unfortunately backspacing is not measured from the bead, it's measured from the outer edge of the casting. Typically a wheel is 3/4"-1" wider overall than its "nominal" width. Your 6" wheel might be 7" total width so that 3.25" backspacing puts the wheel mounting surface 1/4"
in from the centerline of the wheel. Which is why I much prefer to specify mounting-surface-to-centerline rather than backspacing.
