Wheel backspace and tire size

[19 69 GTX]

Ok got a 65 Coronet with ss spring that have the offset shackles. Just wondering what is the widest tire I can fit and correct backspace. Stock wheels just as springs with the offset shackles. I had a 65 once but not long. It had stock springs and stock location. I put 275/60/15 on it and they fit nice but cant remember backspace. I have done some measurements and seems like a 295/50/15 wouldn't fit. So if I go 275/60/15 again what backspace 4 or 4.5 on an 8 inch wheel. Let's see some pics , tire , size , wheel and backspace

 

[33 IMP]

Ive got a 62 savoy with a 10.5x28 slick that barely fits with spring in the stock location. I have about a finger width to the fender, and a finger width to the springs. They are on a 15x8.5 centerline with 4 7/8 backspace, with a .300 spacer, so almost exactly 4.5 effective bs.
I also have a 10x28 slick on a 4 1/2 bs tt2, that fits much better, the 1/2 makes a lot of difference.

 

[glorydays]

Ive got a 62 savoy with a 10.5x28 slick that barely fits with spring in the stock location. I have about a finger width to the fender, and a finger width to the springs. They are on a 15x8.5 centerline with 4 7/8 backspace, with a .300 spacer, so almost exactly 4.5 effective bs.
I also have a 10x28 slick on a 4 1/2 bs tt2, that fits much better, the 1/2 makes a lot of difference.

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U like them autodrags? I was thinking about getting some for my ride...