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Drops is getting cut at least in half, but a skinny 30 would fit even that low until a bug lands in bed then your rubbing. Most likely going to be 2 inch drop and around a 28 inch tire.

A 30-inch tire is a tall tire to put on a 57 Ranchero/w 4-inch drop.

Im looking into adjusting speed with tire size instead of changing gearing, going from a 26" tire to under 30 inch i have a 57 ranchero with a 4" drop blocks (too much), 15x8 4.5bs welds with a 215/65/15 (26") with only contact coming from driveshaft to body when i was picking up a 292 and fmx. mearuing it looks like backspacing of 5.5" is safe and can use a fairly tall tire without any close contact areas.  the issue i come across is the fender rolling in, limiting me to sections width around 9 and tread width under 8.

I’m running 225/60 15’s front, 7” with 3.5 backspace. 235/60 15’s rear, 7” with 4” backspacing. It’s on a bird, and really tight. Measure close on the front, (it’s the same suspension). With the sidewall to the upper ball joint can get tight. I think 55blacktie’s info is really good.

I don’t have a clue on the outside edge clearance on a full size car, but if disc are installed or in the future, some move the wheel out a bit. Might consider that. t

The problem is it’s getting increasingly difficult to find really good tires in 15’s and worse in 14’s. On a performed level, we been passed by. The BFG T/A’s on my car when new, were not near the tire they were in years past. But I can get passed the look of a 16/17/18 on a 50’s car. Let alone the 20+ stuff.

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ

Two owners of 55 Victorias posted on the Jalopy Journal that they installed 15 x 6 wheels/w 3.625-inch backspacing, and they fit perfectly. However, they did not mention tire size or whether they have skirts. 

Nine years ago, DryLakesRacer posted on this forum that he put 215/75R15 tires on his stock rims on his 56 Victoria and had no clearance issues with his skirts. He ran it that way for three years. 

I would try 15 x 6 with a 3.625 backspacing. Hopefully, someone with a 55/56 Crown Vic will comment. 

Ok I will look at using 6" rims on the 215's.   I have not bought any rims yet.  I thought I would buy one rim first and put a used 215 tire on it to see how things work out..  Do you have any recommendations on what backspacing would be best?.
Thanks, Ray

What is the backspacing of those 7-inch rims? Unless you already have the rims, 6-inch-wide rims will work fine for 215/75R15 tires. I temporarily mounted throw-away 215/70R15 tires on my OEM 5-inch steel wheels, just so I would have tires and wheels on the car during restoration, but 5-inch wheels are a bit narrow for 215 tires.  

Sir,

       Thank you for your input.  I think I am going to try 7" rims with 215/75/15 rims on my 1955 Ford Crown Vic.  If it ends up that I can't use my fender skirts it won't be the end of the world. I will keep you posted on how things work out.

Thanks, 
Ray