My 55 bird has 15x7 3 1/2” backspace front, mounting 225/60 15 TA radials
15x7 4” backspace rear, mounting 235/60 15 TA radials

The front has the wheel mounting surface out about 1/8” due to the disc brake conversions I’m using.
The rear end is a tri 4 bar. I did have 15x7 rear rims, 4” backspace with 10” cheater slicks at one time.

I had to center the body on the frame in the rear to get the tires to clear. Very tight fit.

The clearance between the sidewall and the upper ball joint is close enough I can’t get the tip of my little finger in there. But it never touches.

Your section measurements will be less with the 205’s, depending on who’s tire you buy.

A friend has 205’s on 6”x15, 3 1/2” backspace on a 57 bird. They just went on, no problem.

Depending on your car, where the body sits on the frame, etc. it’s critical at my combination. My car also has a 56 door jamb and rear quarter panel that was braised on 1/4” low at the taillight. That didn’t affect the tire fitment, but these are old cars with who knows what work was done.



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

I’m not sure what your asking K, but you jogged my memory. My wheels came from a regional chain tire store. They did the measuring and guaranteed the wheels would fit. They were a catalog special order from American Racing wheels. I was on my own for the tires because I ordered them from Diamond Back to get the sidewall I wanted. But they helped me measure for that too when I ordered the wheels. Just a few bucks more than the low internet price and welll worth the service.

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

Here's what I'm thinking,  Follow me on this and see if I have it right.

The steel wheels that are on my car now are 6" in width total.  The center line of the wheel should be at 3".   The distance from the wheel mounting pad and the inside edge of the rim is 3 5/8".  This means the center line of the wheel is 5/8" offset to the inside. 

The American Racing website says the new wheels are 7" wide.  The center line of this wheel should be at 3 1/2"   They say the backspacing is 4".  Does this mean the center line of this wheel is offset 1/2 inch to the inside of the car?

I will be using the same 215/70R15 tires that are on the steel wheels now.  If my logic is correct the new wheel should be almost the same as I have now?

You have center line right.

Backspace is measured from the brake side of the wheel, the side that you cannot see when the wheel is installed.  That means you have +5/8" offset which shifts the center line 5/8" toward the center of the vehicle.

The AR wheel spec is 7", which means that it is about 8" wide, which puts the center line at 4" which means that it has 0 offset.  They usually list these specs on their website so no guessing has to be made.

Offset is usually given in mm so 5/8" is about 16mm


Lawrenceville, GA

Since you’re looking at one wheel, you don’t need an adjustable fitment tool. You can make one out of plywood, heavy cardboard and coat hanger wire.


https://www.jegs.com/i/Percy's/760/01201/10002/-1?CAWELAID=1710534765&CAGPSPN=pla&CAAGID=44693592161&CATCI=pla-224363292311&CATARGETID=230006180039218438&cadevice=t&jegspromo=nonbrand&gclid=EAIaIQobChMIgeOo6Paf3wIVksVkCh3OgQ9YEAQYASABEgL7qPD_BwE


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

I'm confused.  Isn't a 7" wide wheel 7" wide in total outside to outside?

No.  The specified wheel width is the width between beads.  Total width is about 1" wider, outside to outside.


Lawrenceville, GA

Not on a Bird but I have 6" wide Torque Thrust and 75 series tires and everything clears on a 56 car includeing the skirts. With the new style wheels look at getting Gorilla Lugs with the shank that goes into the wheel 3/8" extra instead of just lug that fastens to the angle of the wheel. The old style flat washer and full shank lug is gone unless special order.

56 Vic, B'Ville 200 MPH Club Member, So Cal.

The original KH wheels that came on my "56 bird (riveted construction) do not have the mounting face centered under the tire centerline. I was warned about this by another bird owner - and it rings in my head that that backspace was 3.5 to the rim edge. 




 
 Steve Metzger       Tucson, Arizona

I called tech support about the measurements of these wheels. Here's what they told me.  7" wheels are 7" wide from outside edge to inside edge.   The 4" backspacing is from the mounting pad to the farthest inside edge of the wheel.  This should mean the wheels are offset 1/2" to the inside of the car as the center line is 3 1/2".  My steel wheels are 6" wide in total outside width.  My steel wheel backspacing as measured above is 3 5/8". This should mean my steel wheels are offset 5/8" to the inside of the car. I have at least 2" extra clearance both inside and outside with the steel wheels now.  I believe these Ansen Sprint wheels will fit my car.  I would hate to order them and find out differently.  Anything wrong with my calculations?