I've not had my hands on a full sized '55 / '56 passenger car but it sure looks like the oem wheels were the same size as the T-Birds, 15 x 5.
I didn't find any mention of wheel offset.
See this link...
They were the same. The A frames and ball joints are the same, and the 3.5" backspace is the critical dimension for the tire to clear the upper ball joint. My 15x7 wheels, 3.5" backspace and 225/60 15 t/a's are as tight as you could go.
Ford didn't build anything twice in those days. The shifter knob on a manual Thunderbird is the same as Ford tractors . It's cheaper at the tractor store.
OK, I've been looking at this thread for awhile and just wanted to question the answers given. I could easily be wrong but it seems to me that my 55 bird and a 55 ford wagon came from the factory with the same wheels, Passenger cars were slightly different and I can't remember just how but I recall in offset or rim width. Both could be interchanged however. All these wheels I had were Kelsey-Hayes.
I guess you could be right. I was basing my answer on the interchange, from almost 50 years ago, when I mounted snow tires on the pass car rim. All I really remember for sure is they both could use the dog dish hub caps.
I haven't found anything online about another oem wheel width or off-set specs for '55/'56 full sized car wheels.
There is this Coker Tire page for Ford reproduction steel wheels with a wheel size menu. https://www.cokertire.com/o-e-style-ford-wheel-primed.html
The backspace measurement listed for their 15x5 wheel is: 3 inches.
You're welcome. The 50 year old stuff is getting hazy. But so is last week. Looking back, those wheels came off a wagon, possibly the same one the rear end came out of. But I sure don't recall any wheels narrower than 5". I wouldn't have caught a minor offset difference if the tires cleared. And I never would have looked for a different manufacturers marks.