73 dart...B body 8.75...what size wheel/tire

Tires and Wheels (Mopar Hubcaps Too)

  1. mc-g

    mc-g Well-Known Member

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    As the title states. I know the biggest tire and wheel size has been asked a ton.....but does anyone know what backspacing and offset I would need for a b body rear end under a dart. what say you
     
  2. Bad Sport

    Bad Sport HALF A BUBBLE OFF Staff Member FABO Gold Member

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    If you already have it under there measure the spacing to be sure.

    To measure for the backspace, take a straight edge that is at least as large as the wheel/tire combination you plan to use, and place it against the brake drum (or rotor face if using disc brakes) where the wheel mounts. Now you can take a measuring device (tape measure or ruler), and measure the distance from the straight edge to the part of the car's suspension, brake system, or whatever, that is closest to the straight edge, AND that is outside of the wheel's diameter. You'll also have to make sure that if using an aftermarket disc brake kit that the brakes will fit inside of the rim's diameter. If you measure from the inside diameter of the rim's bead-edge, there should be nothing within 1 inch of it. We have found this gives the tire enough room for expansion when mounted, and flex when cornering.

    The next measurement you need to get is the overall rim width. Again, measure using the straight edge and a ruler to find out how wide a wheel will fit in your opening[FONT=&quot]—[/FONT][FONT=&quot]remember to leave about 1inch [/FONT][FONT=&quot]of clearance on each rim edge (inner and outer).[/FONT]

    When you are comfortable with the measurements you have taken, now you need to decide what tire will fit your wheel and opening. Tires have a couple of measurements you need to pay attention to[FONT=&quot]—[/FONT][FONT=&quot]section width, tread width, sidewall height, and overall diameter. Section width is the actual width of the sidewall at its widest point after the tire is mounted and inflated. It's this measurement that gives [/FONT][FONT=&quot]cause for the 1 %-inch spacing between the rim edges and the vehicle. Tread width is self explanatory; [/FONT][FONT=&quot]it's the width of the tread pattern. Sidewall height is the distance from the rim to the tread, and overall [/FONT][FONT=&quot]diameter is, well, the diameter of the tire after mounted.[/FONT]


    There is some good info here: http://www.moparmusclemagazine.com/techarticles/drivetrain/mopp_0404_8_3_4_rear_axle_housing_swap/

    Hope this helps
     
  3. 72bluNblu

    72bluNblu FABO Gold Member FABO Gold Member

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    Badsport is right, best way is to measure.

    Also, it matters WHICH b-body rear you have, as they are NOT all the same. This isn't the holy grail, but here's a better idea about B rears

    B BODY 8 3/4- Drum to Drum

    '62-'63= 58 1/2" (And '64 Max Wedge)
    '64 = 60 7/8" (Exc.Max Wedge)
    '65-'67= 59 1/2"
    '68-'70= 60 1/8"
    '71-'74= 63"
    '71-'73 wagon= 64 3/8"

    A body rear is 57 1/8" drum to drum.

    So, if you've got a '68-'70 rear, you're looking at 3" overall, or 1.5" on each side. Given that a 4.5" backspace is what you usually want for a 7" or 8" rim to get the tire the fender and without hitting the springs, I'd start around 6" of backspace.

    But, that's just a ballpark. Dart's don't have a ton of space in the rear wheel wells, so if you're looking to fit the biggest wheel possible you'll have to measure.
     
  4. a1972dartswinge

    a1972dartswinge Well-Known Member

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    Depends on what year B-body housing you have. There are Five different versions, all different widths and spring perch location...

    B BODY
    '62-'63= 53 1/4" (And '64 Max Wedge)
    '64 = 55 5/8" (Exc. Max Wedge)
    '65-'67= 54 1/4"
    '68-'70= 54 15/16"
    '71-'74= 57 7/8"
    '71-'73 wagon= 59 7/16"

    This should be easy to figure out once you identify which one you have.

    I run a FACTORY 8 3/4" rear housing, and I fit a 15x8 rim, with 4.5" backspace, with 255 60r15 tire, Perfectly on the back of my 72 dart.

    "Googling" '8 3/4 rear end dimensions' tells us that;

    Factory A-body flange to flange is 52 5/8"...
    ...so just figure out the difference in width flange to flange, divide it by two, and you will have how much longer the housing 'sticks out' from the factory A-body location...

    For example.
    If we go with the 65-67 B-body housing, the difference in overall flange to flange length is 1 5/8". Divide that by 2, and you get 13/16". That is how much more the tube will stick out past factory A-body housing location.

    So you need a wheel that is roughly 13/16" more backspace than the baseline. I used 15x8 with 4.5" BS as my baseline since I know that fits centered in the wheel housing.

    May sound confusing but play around with it on paper and it works out well. I'd run a 5"-5.5" backspace wheel and that will get you close to center, depending on how wide you order the wheel.
     
  5. a1972dartswinge

    a1972dartswinge Well-Known Member

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    Ha looks like 72blu was writing up a post about the same time I was tooling around with it. I guess he's right, trying to be precise like I am may not be the best way, because there's always a variation somewhere. So I guess start with grabbing some straight edges and a tape measure and get to it.
     
  6. a1972dartswinge

    a1972dartswinge Well-Known Member

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    And the "theory" post I made was assuming you're going to be using A-body drum brake backing plates/etc. B-body is wider and beefier so that throws your overall dimension off.
     
  7. mc-g

    mc-g Well-Known Member

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    awesome guys! THANK YOU for these posts. The science of wheel measurements has always been foggy. You describe it better than pictures. I don't have the rear end yet. I DO know its a '68. I'm wanting to run 15" steelies or torque thrust D's. I'll get to measuring once its all mounted up
     
  8. 72bluNblu

    72bluNblu FABO Gold Member FABO Gold Member

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    Ma Mopar wasn't the greatest with "fit and finish", lots of variations from car to car.

    Plus, as our posts show, it really does depend on which B housing you have. I went with the drum to drum measurements also, as flange to flange doesn't take into account the different width on the brakes, different offset on the axles etc.

    Figure out which rear end you have and you can get pretty close. And if you're not stuffing the biggest tire you can in there, that's ok. But if you want to maximize your tire, you really have to measure your car, as it will probably be different than mine. Heck, my Challenger has a touch of tire rub on the passenger side, NOTHING on the driver's side. Set up is exactly the same side to side, so, that tells you the CAR isn't exactly the same side to side.
     
  9. 72bluNblu

    72bluNblu FABO Gold Member FABO Gold Member

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    How big of a tire do you want to run?

    If you're going to run a B rear and move the perches, I'd get an offset hanger kit too. No need to do the full 3" relocation, but you might as well get the extra 1/2" to 3/4" since you're moving the perches already.

    15" steelies might be hard to get the most out of unless you go custom, I don't think they have anything in the 6" backspace range. Torque thrusts would be easier to get in that kind of offset. And if you go with offset hangers, you can add some more backspace as well.
     
  10. crackedback

    crackedback FABO Gold Member FABO Gold Member

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    What about the difference in standoff distance between SBP and BBP?

    Look at teh sticky, top of this forum about wheel/tire combos.
     
  11. oldkimmer

    oldkimmer FABO Gold Member FABO Gold Member

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    ...........I have a rear out of a 68 road runner in my 74 duster.........my rims are 15x10 in wide centerlines with 5in back space.....have p295/50r15 gy eagle gt2s........i have 1 3/4 in to my springs from the tire buldge.......my tires stick out about an inch, so 6in bs would be better on my car.......kim........
     
  12. a1972dartswinge

    a1972dartswinge Well-Known Member

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    Sure sounds about right that you need 6" BS because a Wheel Vintiques Mopar reproduction 15x10 wheel is 5.5" BS as a 'mass production' aftermarket wheel, and your B housing is wider than an A.
     
  13. mc-g

    mc-g Well-Known Member

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    Well, all I could get was a complete E body setup. BUT....there a local guy who cuts axles and housings, and does the re-splining.....all for $150. He's GOOD too. So now I can rock any width. I'm gonna take him my junk 7.25 with the 8.75.....and just have him match it up to the current width.
     
  14. OwdKasd

    OwdKasd Well-Known Member

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    You still may want to have the Rims in hand that you will be using. You may end up an inch or two different than the 7 1/4 for a perfect fit. My Outlaw 2's have about a 5" backspace and are almost perfectly centred. If you end up with say a 3" backspace then you may want to go narrower when do it. I hope that makes sense/Helps you. Gerry
     
  15. mopardude318

    mopardude318 Well-Known Member

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    on my A body with a B rear, i use 17x8 with 5.72 backspace...
     
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