Had 15x8s on the car for AGES before switching out.
They were 3-3/4 BS. Loads of room on the backside. Cleared the fenders on the outside fine.

New rears are 18x9.5" www.vintagewheelworks.com V45s. 5.5" standard BS with 275/45-18 Michelins. Enough room on the backside, maybe 3/4" or so. Enough room on the frontside to go to 18x10" on my car with same 5.5" BS. BUT, my rear fender lips are rolled up in the inside. Without the roll, they'd still fit, but on a wider wheel, it might be dicey. Springs are in factory location.

I wanted something just slightly taller, tire-wise, but the tires I wanted weren't available in 285/45 or 295/45-18. The 275s fit perfect on the rims, but they are just barely wider than the rims, so I'll have to be careful of curbs.

Fronts are 17x8, with 245/45-17s. 4.5" standard BS. Fit fine. IF I had to do over, I'd have gone with 4" BS to make the frontside look slightly more deep dish/old school, and to match better the dish depth appearance of the rears.

If I get a chance this weekend between work and kids, I'll try to post a pic.