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By Florida_Phil - 6 Years Ago
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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!
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By charliemccraney - 6 Years Ago
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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.
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By Florida_Phil - 6 Years Ago
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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.
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By Florida_Phil - 6 Years Ago
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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.
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By Florida_Phil - 6 Years Ago
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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.
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By charliemccraney - 6 Years Ago
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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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By Joe-JDC - 6 Years Ago
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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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By Vic Correnti - 6 Years Ago
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Right on Joe!
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By charliemccraney - 6 Years Ago
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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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By GREENBIRD56 - 6 Years Ago
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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.
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By miker - 6 Years Ago
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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.
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By miker - 6 Years Ago
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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.
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By Florida_Phil - 6 Years Ago
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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?
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By charliemccraney - 6 Years Ago
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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
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By miker - 6 Years Ago
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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
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By Florida_Phil - 6 Years Ago
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I'm confused. Isn't a 7" wide wheel 7" wide in total outside to outside?
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By charliemccraney - 6 Years Ago
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No. The specified wheel width is the width between beads. Total width is about 1" wider, outside to outside.
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By DryLakesRacer - 6 Years Ago
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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.
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By GREENBIRD56 - 6 Years Ago
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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.
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By Florida_Phil - 6 Years Ago
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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?
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By Pete 55Tbird - 6 Years Ago
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Phil
You wrote ". 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?"
You should not have to do ANY CALCULATION, get TECH SUPPORT to do it for you BEFORE you BUY the wheels. Pete
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By charliemccraney - 6 Years Ago
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Tech support is wrong or you misunderstood.
You can see the specs here, https://www.americanracing.com/wheel/8845/vna69-ansen-sprint
The 7" rim has 0 offset and 4" backspace. The only way that is possible is if the wheel is 8" wide overall. The 7" width is measured between the bead, the part of the wheel that the tire actually touches
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By KULTULZ - 6 Years Ago
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Man, you guys are beating yourselves to death over this.
There are only three ways to get where you want to go-
1) Order the wheels in the exact size as your present wheels
2) Get dirty and use a tool such as shown below.
3) Or hire a professional as Mike did to do it for you.
There are just too many variables as outlined on the post thread before this one. What works on one car (even same type) may not work on another. If you change over now without ensuring the suspension- trim height are not correct or where you want them, any future modifications are going to lead to heartbreak.
Too many theories being thrown around to create confusion.
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By Florida_Phil - 6 Years Ago
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I decided to put my wire wheel hub caps back on with the black wall tires and no skirts. I like it. Kind of classy and hot rod at the same time.
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By Florida_Phil - 6 Years Ago
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Charlie is right. I emailed American Racing Tech Support directly. Here's what they had to say. No wonder there is so much confusion. Even the Vendors can't get it right.
The overall width of a wheel is always 1” wider then its advertised width. This is because wheel width is measured from bead seat to bead seat. This is true for all wheels. Therefore, our 15x7 VNA69 has an overall width of 8”. The 4” backspace is measured from the outer edge of the wheel down to the mounting pad.
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By KULTULZ - 6 Years Ago
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And what that is doing is protecting the maker. Total width has to be included so the ordered wheel doesn't hit something such as a ball joint. The other measurement is for tire sizing.
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By paul2748 - 6 Years Ago
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Advertised wheel width is typically the measurement on the inside of the bead as mentioned by American Racing. Adding an inch for the the overall width (outside of the flange) is probably typical of steel wheels. Aluminum wheels may be different.
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By MplsMike - 6 Years Ago
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Hi Kultulz,
What’s the name of that tool you posted and do you know where to buy it? Thanks,
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By miker - 6 Years Ago
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Mike, the jegs link in my previous post is for the measuring tool. I’ve got one, they work.
If you cut it a bit close, you buy this next. Didn’t need it on the bird, but have used it successfully on OT cars.
https://www.eastwood.com/ew-fender-roller-w-instruction.html?SRCCODE=PLA00010&gclid=EAIaIQobChMI5q3rj_us3wIVE8pkCh0ASANrEAQYAiABEgJ-fPD_BwE
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By MplsMike - 5 Years Ago
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Thanks Miker for pointing out the link you posted. My turn next on trying to fit wheels and tires.
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