Currently on my 67 Skylark I have 18x8 w/ 245/45 in the front along with 18x9.5 w/ 274/45 rear. The rear wheels are a -4 offset right now. I don't road course this car but I do beat on it any occasion I get with most driving being cruising around the lakes. My front tires rub on turns so I plan on taking off the stainless trim and rolling the fenders. In the rear I have issues with my tires rubbing on hard turns or on beveled (best way to describe it) entryways/ driveways. Currently my tires in the rear have between 1/16 and 1/8 of an inch between the quarter and the tire itself. The previous owner cut out the inner panel to make the tires fit. There is almost exactly 2 inches between the tire and the frame/inside tub of the wheel well. That being said. I'm in the process of getting a 9" that may very well be exactly 2 inches narrower than my current rear end which would leave my current wheel application with 1" inside and outside of the rear tires. Which will be good for now, but the plan is to get wider tires and wheels. Do you guys think I will be able to run an 11" wide wheel with a 305 on it once I get the slightly narrowed rear end? My current NT555 are just shy of 11" wide at 10.94 and the 305 (Nt555R) would be right about 12.13 inches wide. I'd end up getting a 0 offset wheel, and going essentially 1.2 inches wider. This would end up giving me, if all calculations are correct, about 3/8" on either side of the tire. Potentially 5/16 on the inside and 7/16 on the outside because of my current -4 offset changing to a 0. I do also plan on raising the rear up about an inch, it its too low for my liking and is flat, not raked like I would prefer. If not I'll end up having to notch the frame and if I get to that point I might as well plan on not driving my car for 5 years. . . . and well I don't want to do that. Anyone here be able to give me some pointers?
Not sure anyone will be able to even venture a guess for you. I'm not sure what -4 offset is, but I'm guessing it means -4mm? That 's next to nothing. IMO, you are so much better measuring back space since that is so much easier to measure. Offset is measured from the center of the wheel width. An 11" wide wheel is actually closer to, if not 12" wide. A 0 offset 11" wheel should have close to 6" of back space. A 67 Buick would normally need more back space than a 70-72 Buick A body. The biggest wheel I know of for the 70-72 Skylark/GS is a 10" wide wheel (11" overall), needs 5 1/2- 5 5/8" back spacing. I would wait until you have the narrowed rear installed, then measure from the wheel mounting of the drum or disc, and see where you are.
Yes the -4 means 4mm, which as you said is next to nothing, but that also means these 9.5" wheels practically have a 4.75" backspacing. Also none of these numbers really mean anything. The thing I need to find out is what's the closest people run their wheels and tires to the inside of the 1/4 and frame.
On some of my '66's, I can fit a fingertip between the tire and quarter panel lip, or about 1/2". It will rub under some conditions, I'd recommend more clearance.
