How to roll a fender lip?

halfafish said
I got the car off the jacks and on its feet. When I lowered the first side I was pretty excited as I was showing a fat 1/4" clearance to the fender lip. However, when I set the other side down I have virtually NO clearance to the fender lip. I can slide a couple of pieces of paper in there, but that's it.

And now I recall how I got in this spot. When I mocked up the axle, brakes, and wheels I used my old SBP axles that were re-drilled for BBP. Then when Dr. Diff's axles show up my clearance is gone. Boohoo.

View attachment 1715579223

Yup, if you measured with SBP axles that were re-drilled you lost over a 1/4” going to the real BBP axles.

The lip in that picture already appears to have been trimmed back too, btw. Which means you can’t trim much if anything without getting into the spot welds. It also means even if you rolled it flat your clearance to the quarter would be marginal. Which means new rims would be the better solution.

As for the rims, if you have a 15x7” with 4.25” backspace now, going to a 15x8 with 4.5” would be worse. That’s one reason it’s good to look at offset too. A 15x7” with 4.25” of backspace is a +6 offset. A 15x8 with 4.5” of backspace is a 0 offset. Which means the centerline of the rim moved out toward the quarter by a 1/4”. The offset gives the centerline of the wheel, so, when you change rim widths and you want the centerline to stay the same you can look at the offset number.

In your case, if you’ve got an 1” or better to the springs and nothing to the quarter, you need another 1/2” of backspace or an additional +12 of offset for a total of +18. That means your 7” rim should have a 4.75” backspace, and your 8” should have 5.25”.

The rims I’m gonna buy for my ‘71 dart are 17x8 with a 5.25” backspace. It has an A-body rear with BBP axles too. On my car by my math that will put them pretty close to the springs. But if they’re too close a spacer solves the problem. If you go too little offset you get to work on the quarters, or buy new rims.