Help with Wheel and tire combo please!
IMHO a wheel any bigger than 16" looks "wrong" on a '70s car.
For the most part, I agree. I prefer the look of a taller sidewall and a 14"-15" wheel.
But as it's already been pointed out, there isn't a lot of tire selection for a 15" rim. BFG T/As and Cooper Cobras for the most part, some rubber from Nexen and Kumho, maybe the Uniroyal Tiger Paw if you can live with something like a 225/60. None of them are fantastic, although I've run the Cobras before and they're not bad considering their price point. Speaking of price, you can spend major $$$ on repop Firestone Wide Ovals, but I'm thinking that's outside the lines for most folks (me included).
And wheels? There aren't many wheel choices in 15" either, if you're running the SBP.
The LBP guys have it a bit easier. For starters, they have a bigger selection of rims in 15". And since Mustangs run the same 5 x 4.5", there are a ton of wheel styles out there in 16", 17" and 18" sizes, with all sorts of backspacing and offsets. I think a 16" wheel is a decent compromise on older Mopars - bigger than I like, but the tire selection is much broader, and they don't look too ridiculous if you pair them with something with a decent sidewall.