Technical Found some wheels , need tire suggestions

www.willtheyfit.com

a very helpful tool

 

I like the visual of roughly how much the sidewall will bulge.

 

A 255/60 on the rear would be a great look for your car (it's what I think I'm putting on my 62 Bel Air soon), however on a 7" there will be a lot of bulge to the sidewall, too much can look goofy. If you want matching heights, a 215/70 matches a 255/60 in height but looks best on a 7" wide wheel with just the right bulge.

Those wheels you have seem to be all 7's, with the different widths you want 7's and 8's might be better, otherwise I would stick to maybe a 235 in the rear at most.

I use this to compare tire sizes. https://tiresize.com/comparison/

 

15x7's all around. 23575R15's rear, 21575R15's up front. 60 series tires will look goofy on your (very nice looking) '56. Something with some sidewall will look, and drive, much better.

 

Both Cooper and BFG say the 255/60 can be used on a 7. If you like sidewall bulge, go with the 255. 215/70 for the front will match the height, and 60 series for the front will be a tad shorter.

 

A 255 tire is a bit too wide for a 7" wheel, and is not ideal for handling. The less vertical the sidewall of the tire is when mounted on the wheel the more it will flex and deform under load, which can give a less stable feeling. It makes the tire a bit too "squishy", for want of a better description. I would suggest 235 maximum and 195 minimum for a 7" wheel. For a 255 tire you need wheels at 8" wide.

Good idea to also check that the offset of the wheels will work with such a wide tire? Space in the wheel well will be a concern if the offset is not spot on.

 

When multiple tire manufacturers specify a 7-9" wide wheel for a 255, of course an 8" wheel is the sweet spot and that tire on a 7" will be less stable. However, let's be honest that a 56 Chevy isn't a performance car and you may not really notice the difference.

My brother ran 285/70R15 radial TA's on an 8 inch wheel. Ideal? No. Work fine? Yep.

 

If you like things a little spongy and "boaty"then yes, a 255 on a 7" wheel will work....... but not ideal.
Besides, a little more dish with an 8" will look better.... yes?