[martrogers]

Sambo

I have 17" Vintage Wheel Works wheels but not on a Harrison so I dont know if this will be of interest to you.

Anyway, I got Eli to send me dimensioned cross sections of the rims - it turned out that the backspace is measured from the inside of the rim (where the tyre presses against). The rim then turns out 12mm and the tyre bulges out beyond that.

This is probably important if you're tight for space.

Let me know if you want me to send you the diagram.