Someone tell me I ordered the right thing please

Mopar General Discussions

  1. sbmopar318

    sbmopar318 Well-Known Member

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    Ordered classic industries 15x8 4.5 Back Space SBP for my 70 dart. My math said that was the correct back spacing to allow for the most tire am I correct?? Also with stock springs what’s the biggest tire I can run or should I put SS springs in ??
     
  2. 33IMP

    33IMP Well-Known Member

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    You should be good with the wheels. Pull a wheel off and bolt your new wheel on, without a tire, support the axle with a jacket and at ride height, and measure to the springs, the Inner and outer fender. Then do the same on the other side .(lots of cars vary from side to side.
    The measurements will tell you how much you can run on YOUR car, on YOUR wheels.. Much better than a guess from somebody on the internet.
    Edit: JACKSTAND, not a jacket, damn auto correct.
    I heard the guy that invented auto correct died recently. May he rust in piss.
     
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    • Jeff Seighman

      Jeff Seighman not my real name

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      With that back space I think it would put most tires to close or rubbing on the fender lip, I have a 70 Dart with 15x7, 4 1/4 back space with offset spring hangers, tires are 255/60/15 and I cut the lip to the pinch welds and have a little more than a 1/2 inch space, there is more than an inch from tire to leaf spring and the car is lower than stock.

      Jeff
       
    • jbc426

      jbc426 Well-Known Member

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      I'm running that size rim with a 275/60-15 tire on my '68 Barracuda. No rubbing even on the roughest roads or hardest launches. I used two passenger side 3200lbs SS springs, sway bar, properly adjusted slapper bars and Koni shocks.

      When it becomes time to replace those Koni's I'll buy the QA-1 single adjustable shocks like I did on the front. Great shock for the money and the adjustment range is spot on.

      B1.jpg

      Spring Fling.PNG
       
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      • abodyjoe

        abodyjoe Well-Known Member

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        I have 15x7 with 4.5 backspace on our dart. An extra inch of rim seems like it's gonna be tight on the fender well.
         
      • dartindanno

        dartindanno Well-Known Member

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        I ran 15x7's 4.25 backspacing with a 255/60/15 tire no problem on my 70 Dart. When I switched to 15x8 4.5 backspacing the biggest tire I could fit was a 235/60/15 and it's really close the quarter
         
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        • 33IMP

          33IMP Well-Known Member

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          Yeah, ain't it amazing that with a wider wheel, you have to mount a narrower tire!
          That's a direct function of most of the extra width being added on the fenderwell side.
          I've got some 15x8 old style one piece mags that I can't really put any wide tire on, and same brand and wheel in a 15x7 that I can put two sizes bigger on.
           
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          • mvh

            mvh FABO Gold Member FABO Gold Member

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            JBC — that's a very large diameter tire... my chart says 28". Amazed you got that in there. Surprised you didn't go to a 50 profile.
             
          • toolmanmike

            toolmanmike Moderator Staff Member FABO Gold Member

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            You may have issues with the 8" wide wheels on a Dart. I also have 7"s with 255-60/15's And they are a tight fit on the quarter panel side. A finger's width of clearance on the spring side and not even my pinkie on the quarter panel side. And that's with the back up quite a ways. @sbmopar318

            001.jpg
             
            Last edited: Oct 6, 2021
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            • AJ/FormS

              AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s FABO Gold Member

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              You might as well get used to the idea of moving the springs AND narrowing the rear end, lol.
              Try this;
              Remove a wheel, support the axle at ride height. Measure from the inner edge of the outter lip to the back wall ..... where the sidewalls will be. You will probably have to drop plumblines to a sheet of cardboard taped to the floor.
              Subtract 1 inch for tire clearance (total for two sides), then convert your measurement to metric by multiplying by 2.54...That will be the maximim size of INSTALLED sidewall that you can fit in there.
              Now, realize that when you buy a tire these days, the number stamped on it, was arrived at, by installing it on a rim that was 70% of the stamped size..
              For example;
              a tire designed to be a 255, was installed on a rim of 255 x 70%=178.5mm, = 7'' in USA measurement. Then the tire was verified to be in the range of 250 to 260 mm wide, and stamped 255.
              If you put that 255 tire on an 8" rim, the section width will grow about 3/4 inch, which is .75 x 254=19mm, so your new section width will be between 269mm and 279! So don't screw up!
              IMO for long tread life, the 70% rule is too small and should actually be closer to 80/85%, the bigger the tire the closer to 85%.
              So let say your measurement is 12inches which, less the 1 for clearance, is 11 which is 279mm.
              Now lets say you want to put that 255 on a rim of 80%. That would be about 223 mm or 8.8. The closest size to that is an 8.5(216mm).
              Now to that, you add your anticipated sidewall bulge of about 1.5 inches total=38mm. So now yur up to 216 plus 38=254mm there you go. The closest size to that is a 255 which has an allowable range of 250 to 260 on a 7" rim/ perhaps 269 to 279 on an 8" rim.
              Will the 255 fit?
              @toolmanmike says yes, but just barely. And I'd be willing to bet that he was very nervous when he ordered his bling.
              That's one way to do it.
              Now, to be accurate;
              The distance from the floor to the widest part of your installed tire; when you put that into the wheel tubs, you will find (probably) that where it hits on the back wall, is not where it hits on the outer lip. This will depend on your ride-height. Take a close look at Toolman's Dart; the rear of the car is a lil higher than stock, and so the interference point, on the outside, is up past the widest part of the tire, where the sidewall is curving back towards the tread. This is sortof a normal situation. But if your car is lowered, you HAVE to keep this in mind and you may run into clearance issues that require rolling the lip to cure.
              Furthermore; just because the math says it will fit into the tub, it will only happen if the backspace allows it to, and usually, the springs will have to be moved over.
              If you have NO DESIRE to move the springs, then you have to subtract the interference factor from the measurement to the backwall.
              Earlier I used 12inches in the example, from the lip to the backwall, and allowed a total of 1" clearance. So if your springs are .5 inch to the outboard of the inner wall, you gotta subtract that from the 12inches, and get 11.5.
              However, that .5" automatically gives you more than enough inboard clearance; so where I used 1" total, you can now use as little as 1/8 to the spring. So on the inboardside your total deduction is .625. On the outboard side, with your rideheight like Toolmans, you can reduce your clearance to 3/8. Therefore your total deduction is still 1inch........ but your backspace will need to be recalculated.
              Now, if your car is lowered, the outter lip will drop down towards the widest part of the profile, and you may need to allow an additional .5 or more inch for that.
              And, if you like to blast around the turns, the body is gonna roll over to the outside of the turn , pulling the inboard side of the body, towards the sidewall. So you MAY have to allow for that as well. I solved my problem (my car also is lowered), with poly bushings an extra mainleaf, plus clamps, plus tinsnips, lol.
              Here are a couple of tips for you;
              1) It is always better to have MORE backspace than you anticipate, because you can always space the wheels to the outboard, as may be needed. But if not enough backspace, then yur kindof fubarred.
              2) If you install the max tire height on attempt #1, into a a lowered car, you are just asking for trouble.
              3) rolled lips, IMO, look like crap. I suggest instead, to cut the shelf and fold it up. You might be surprised at how much support that shelf actually provides so don't lean on the lip! after cutting it away.
              4) marry a skinny wife, and make her work for a living. If she gets to be 140 you will want to mention it to her; don't; just get used to the idea that your sex-life is drawing to an end.
               
              Last edited: Oct 6, 2021
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              • abodyjoe

                abodyjoe Well-Known Member

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                here are pics of our 70 dart.

                15x7
                4.5 backspace.
                large bolt pattern axles and c-body drums
                225/60-15 tire.

                DSC_0084.JPG

                DSC_0085.JPG
                 
              • RustyRatRod

                RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                Very cool looking car!
                 
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                • jbc426

                  jbc426 Well-Known Member

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                  I see we are almost neighbors. We should set up a meet, and I'll take you for a test drive. The car runs in the 11's as it is now with a sub 500hp 408 Magnum in it. In a couple of months, I'll be selling this motor and swapping in a supercharged 408 that will bump the output to the mid 800hp range. That should be just about perfect for this old 3700lbs car.
                   
                • DARTLARRY

                  DARTLARRY Well-Known Member

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                  Toolman, what did you use for mud flaps?
                   
                • Killer6

                  Killer6 Well-Known Member

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                  How did You get an A 'cuda up to 3700#?
                   
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                  • Killer6

                    Killer6 Well-Known Member

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                    One thing to look for is the axle centering, this is in other posts, but it's not uncommon for the rear to be off 1/4-3/8". If You plan to push it, it needs to be on center.
                     
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                    • jbc426

                      jbc426 Well-Known Member

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                      Right!

                      I was shocked, and reweighed it on a second scale. They were both within 50 lbs of each other.

                      Here's what is in the car that makes it so heavy.

                      Aluminum headed 408 Magnum with full 3" TTi exhaust, vintage air A/C, 2004R trans with bolt on bellhousing and 3600 rpm lock-up converter, 4" Mark Williams 1350 driveshaft, Dr Diff built 8 3/4" with his Econo Disc kit, front and rear sway bars, 11 2/4" police taxi front discs, a full US Cartool Chassis Stiffening kit, a 4-point rollbar, Corbeau bucket seats, a four row brass radiator, 2 trans coolers and 15" steel rims.

                      Even with all this stuff I was thinking it would be around 3300 lbs.
                       
                    • diymirage

                      diymirage HP@idle > hondaHP@redline

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                      Fixed it for ya
                       
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                      • toolmanmike

                        toolmanmike Moderator Staff Member FABO Gold Member

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                        I don't know what they are. The previous owner put them on. I didn't think they looked too bad and no one has given me grief about them so I kept them on.

                        View attachment 1715802602

                        001.jpgcrop.jpg
                         
                      • sbmopar318

                        sbmopar318 Well-Known Member

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                        Where is everyone finding these 15x7 4.25 BS ?? All I’m finding are 4” BS
                         
                      • Slantsix64

                        Slantsix64 Well-Known Member

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                        Don’t think it’s going to work in your dart 4.5 bs is better for big bolt pattern axles. Better fit would be 15x7 4.25bs with a 255 60 tire

                        on a 67-69 barracuda you can fit a 275 60 15x8 with 4.25 back space small bolt pattern axles with no modifications. On a dart you will need to relocate springs etc.
                         
                      • sbmopar318

                        sbmopar318 Well-Known Member

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                        Yeah I cancelled the order. Now I’m trying to find the 4.25 BS all I’m finding are 4”
                         
                      • 33IMP

                        33IMP Well-Known Member

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                        If that is true, just use a 1/4" billet spacer. No need to move the springs, unless you WANT to.
                        Thats what is nice about "too much" backspace. It can be fixed. Too little and the tire crashes into the outer fender, and that cant be fixed.
                        Edit: i DO agree a 15x7 would probably be a better fit. But his 15x8s are in the mail, i think .
                         
                        Last edited: Oct 8, 2021
                      • Jeff Seighman

                        Jeff Seighman not my real name

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                        If I remember right I got mine from Wheel Vintiques a few years ago, but looking at their site, they don't have them anymore. I can't find them anywhere else! I don't know why they would discontinue them?

                        Jeff
                         
                      • Righty Tighty

                        Righty Tighty FABO Gold Member FABO Gold Member

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                        I've always loved the stance your car has. That picture of your car is the one I found a few years ago when I was searching images to find the right tire/wheel combo for my Scamp. 80D314BA-2C94-41BE-BABC-2D93A904166B.jpeg
                         
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