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Help with 1955 Thunderbird Wheels

Posted By Florida_Phil Last Year
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Florida_Phil
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I am buying a set of 15" American Racing Ansen Sprint wheels for my 1955 Thunderbird and am looking for some input.  I'm not exactly sure how to measure wheels.  My stock steel wheels look to be 5" wide between the mounting flanges with a 3 1/2" backspacing.  I assume this is what came on the car?   The car looks and drives great with these wheels and 215-70R15 tires.   I am not running skirts on the rear.  My car currently has drum brakes. 

The narrowest 15" Ansen Sprint wheels I can find are 7" wide.  They are available with 4" backspacing.  Is anyone running 15" custom wheels on a '55 Bird?  What backspacing do you have?  Thanks!
charliemccraney
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Offset is the best dimension to use. The best way to figure that out is to have the tire off of the wheel for measurement.  You simply measure the overall wheel width and divide by 2 for the center line.  You can then use the backspace to determine the offset of that wheel.
If the tire is still on, then you can make some assumptions to ballpark the figure.  You will need to know the wheel specification and that usually is stamped on the wheel.  A wheel's overall width will be about 1" wider than the specification so a 5" width specification will have about a 6" overall width because the specification is measured between the beads.  That and the measured backspace will get you in the ballpark for the offset of the wheel.

If you will be using tires of the same width then you don't have to do more but if you want to fit the widest:

The other thing you need to know is where the tire is located relative to the inner and outer fender, steering linkage, shocks , springs, etc.  This can be determined simply by measuring.  You can use that information to determine which way you need to shift the offset to get the wheel centered.  Having the wheel centered will allow you to fit the widest wheel and tire combo possible within the available space.

To simplify things for you, the 7"W, 4"BS wheel will move the tire 1/2" closer to the inner fender and 1 1/2" closer to the outer fender vs a 5"W 3.5"BS wheel, everything else equal.  Measure and see if that will work.




Lawrenceville, GA
Florida_Phil
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Thanks for the help.  I need to pull of one of my steel wheels and measure.  I don't think the wheels that are on my are original 1955 wheels.  They seem too wide to me.
Florida_Phil
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The steel wheels that are on my car now are 6" wide from the outside rim edge to inside rim edge (width of wheel on the graphic). The distance between the inside mounting pad and the inside wheel edge is 3 5/8" (negative offset on the graphic).  If the Ansen Sprint wheels are 7" wide with 4" backspacing, where and how much will the Ansen wheels move my 215x70R15 tires?

I have gobs of room in the front.  About 1 3/4" in the back from the tire to the fender.  I don't care if the skirts fit. 

http://forums.y-blocksforever.com/uploads/images/43bacaa4-353e-418b-9702-6f08.jpg
Florida_Phil
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Here's a photo of a 57 TBird with the wheels I want to buy.  Of course we don't know if it's been modified or what the wheel width or offset is.
http://forums.y-blocksforever.com/uploads/images/0fcd7575-5169-420d-b4a4-0e80.jpg
charliemccraney
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The wheels are deeper at the mounting flange so that will move it 3/8" closer to the inner fender.  4 - 3 5/8 = 3/8
The wheels are wider so that will move it 1 5/8" closer to the outer fender.  2 - 3/8 = 1 5/8 (the 7" spec rim will be about 8" wide overall)



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Joe-JDC
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Those pictures are deceptive.  The backspacing is different from centerline measurement.  If you are looking for backspacing, it is from hub/bead area of wheel to the axle face, not rim edge.  Simple to measure with a straight edge laid inside the rim edge on the bead area, and measure the distance to the center of the wheel where the axle flange  is flat.  Just google how to measure wheel backspacing, and you will find a different picture that is the industry standard.  Joe-JDC

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Vic Correnti
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Right on Joe!

  Vic Correnti

charliemccraney
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The one I think Phil edited does show the measurement for backspace incorrectly.

The original picture looks correct in demonstrating backspace, centerline and offset.


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GREENBIRD56
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Phil - take a look at the clearance of the tire sidewall to the ball joint on your car as it sits now. To get mine right (and I've forgotten the total details) I had to figure out the sidewall width of the new tire carcass versus the existing tire. The Thunderbird specific stock wheels for my '56 had a half inch more backspace than a '56 sedan - and I had to use that to figure where the centerline of the tire had to be relative to the mounting face - in order to place the inboard tire clearance where I wanted it.

This works out differently when you change spindles - the later disc brake spindles have the axle CL moved "up" relative to the upper ball joint (guys use this feature to lower the ride height). This moves the clearance point down toward the rim - and allows a bit more inward movement. I say this because if you are buying wheels with the stock spindles in mind - then change to the disc brake version of the upright later - you may wish you had used more backspace. 

   Steve Metzger       Tucson, Arizona

     



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