What is the difference? I understand backspacing but not offset. It seems there are more choices in the forward drive wheel designs than are available for our rear wheel drive 64 -72 A bodies. Can these front wheel drive design wheels be safely used with 1 or 2" spacers on a 71 Elky? What would be the maximum offset one could use with the spacers? Thanks, Scott! graemlins/beers.gif

http://www.discounttire.com/dtc/brochure/info/helpDeskWheelOffsets.jsp

Backspacing is measured from the rear mounting mounting surface (i.e., where the wheel would contact the brake drum) to the outermost edge of the wheel. Typically, you can do this by laying a straightedge across the back of the wheel, then measuring down to the mounting surface.
Offset is measured in positive or negative inches from the centerline of the wheel. An 8-inch wheel with 4.5" of backspacing will have "0" offset. Remember, a wheel will actually measure an inch wider than the bead width...an 8-inch rim is 9 inches wide from edge to edge.

Cool, what about the second part of my question regarding measurment of offset to use on rear drive aand safety issues when spacers are used? Thanks, Scott

Sorry, can't help ya there. I'm not clear on the diffs between front vs. rear drive wheels. There's got to be some experts out there.

With adapters, yes it is OK to use 1-2" adapters and it is just as safe as no adapters. With spacers....HELL NO. Anything more than a 1/4" spacers is too much and unsafe, won't pass tech in any racing organization.

im converting 1965 conv.ss to front disc ihave to have at least a 15 rim what would be a good combo tire size i own 4 15x8 rims with (-11mm)4.5 offset?

"Backspacing is measured from the rear mounting mounting surface (i.e., where the wheel would contact the brake drum) to the outermost edge of the wheel."

Are we talking from the mounting surface to the outermost edge meaning away from the car(what you would see from the street), or to the back (inside) of the wheel edge?

Inside