1.08 torsion bars

Discussion in 'Suspension, Steering and Chassis' started by 5.7 hemi, May 9, 2018.

  1. 5.7 hemi

    5.7 hemi FABO Gold Member FABO Gold Member

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    I’m trying to figure out the rate of the SwayAway 1.08 torsion bars and not finding what they are. Also the online calculators aren’t much help as I don’t know some of the technical stuff they are asking for. Does anybody know or can help me figure out what they are?
     
  2. pishta

    pishta I know I'm right....

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    Chassis: A-Body (35.8" torsion bar length)
    Diam------Orig P/N----ID# MP PN MP ID# RATE-----------APPLICATION
    0.81------P5249148----446,7 82--------------------------------Drag
    0.83------2535888,----9 888,9 92 ------------------------------6-cyl
    0.85------2535890,----1 890,1 101 -----------------------------318
    0.87------2535892,----3 892,3 P5249149 892,3 109 -----------340
    0.89------2535894,----5 894,5 P5249150 894,5 120 -----------383/440
    0.92------P5249151----448,9 137 ------------------------------XHD/Solo
    0.94------2948634,----5 634,5 149 76 --------------------------Police
    0.99------P5249151----450,1 184 -------------------------------Solo,perf
    1.04------P5249153----452 224 ---------------------------------HD solo,roadrace
    1.09------P5249154----453 270 ---------------------------------Circle Track
    1.14------P5249155----454 323 ---------------------------------Circle Track

    another
    0.810" 82 Lb/In SLANT 6/DRAG RACING
    0.870" 109 Lb/In SMALL BLOCK V8/STREET/DRAG RACING
    0.890" 120 Lb/In BIG BLOCK/STREET/DRAG RACING
    0.920" 137 Lb/In PERFORMANCE STREET
    0.990" 184 Lb/In PERFORMANCE STREET/SOLO/TRACK DAY
    1.040" 224 Lb/In PERFORMANCE STREET/SOLO/TRACK DAY/ROAD RACING
    1.090" 270 Lb/In SOLO/TRACK DAY/ROAD RACING/OVAL TRACK
    1.120" 305 Lb/In SOLO/TRACK DAY/ROAD RACING/OVAL TRACK
    1.140" 323 Lb/In SOLO/HD-ROAD RACING/OVAL TRACK
    1.180" 380 Lb/In SOLO/HD-ROAD RACING/OVAL TRACK
    1.200" 396 Lb/In HD-SOLO/HD-ROAD RACING/HD-OVAL TRACK
    1.240" 452 Lb/In HD-SOLO/HD-ROAD RACING/HD-OVAL TRACK
     
    Last edited: May 9, 2018
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    • 67Dart273

      67Dart273 Well-Known Member

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      Can't help but it will "likely" depend on whether you are using the older drum/ disk spindles or the 73/ newer spindles, AND what your wheel offset is.
       
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      • 5.7 hemi

        5.7 hemi FABO Gold Member FABO Gold Member

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        73’ up disc conversion with the 11.87 rotors, 15x7 cop car wheels for the front, stroked 470 with aluminum heads/intake/water pump/housing/aluminum radiator, headers, QA1 k-frame.

        I found this part number P5249154 (1.09) and it says they are 300 inch pounds.
         
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        • pishta

          pishta I know I'm right....

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          1.09 may be 270# unless you got different data but 67Dart273 brought a valid point if your using disks up front you have moved the 'lever' out an inch but all these rates are using the same specs.
           
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          • 5.7 hemi

            5.7 hemi FABO Gold Member FABO Gold Member

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            Does that increase or decrease the effectiveness of the torsion bar?
             
          • 67Dart273

            67Dart273 Well-Known Member

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            Moving the tires outboard by any means makes the springs softer "leverage"
             
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            • 67Dart273

              67Dart273 Well-Known Member

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              I can still remember vomit cans (beetles) back in the day with offset wheels they would start to "camber"

              You can see in this example, the rear "squats"

              315299.jpg
               
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              • pishta

                pishta I know I'm right....

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                its going to decrease. The rated lbs are for a lever 12" long (for instance) if you measure the same torque on an 14 inch bar, you are going to see less lbs at 14 than you are at 12. Like a beam style torque wrench, you have that pivot under the handle at exactly 12 so you are applying the force at the same constant length. So in a case where you are going to increase the front track by an inch, you can probably go 8% over rating and have the same stance as the original drum track. Thats just physics talking, I bet a suspension guy could shed more light on that.
                 
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                • 72bluNblu

                  72bluNblu FABO Gold Member FABO Gold Member

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                  Moving the tires doesn't change a thing with respect to calculating the wheel rate of the bar. The effective length of the lever is controlled by the LCA, from the pivot to the lower ball joint.

                  The center of the tires may change the loads imparted to the lower ball joint because of how they load the spindle, but that doesn't change the length of the LCA. And just because you use later brakes, doesn't necessarily mean you changed the track width. Because that depends on tire offset too. So, even running later brakes, with say, 18" rims and a significant offset, you may end up with a similar track width.

                  The lower control arm is 12.875" long. The "active length" of the bar is ~33.8", 2" shorter than the overall length. If you look at the Sway Away website, their calculator explains that the active length of the bar starts about 1/2 to 1/3 of the way down the radius. If you look at a stock bar, that's about 1" from the end, on both ends.

                  If you input that information, you get 267.4 lb/in for the rate. Which should be about right, if you look at the old Mopar listings for a 1.09" bar. You'd expect it to be about the same with that small of a difference. The thing is, the manufacturer of the bars will sometimes have a slightly different constant for the spring steel they're using, so, different manufacturers don't always publish the same rates for the same size bar. If you look at Firm Feels published rates, they do not match the Mopar Performance published rates. The spring constant they're using is slightly different.

                  As for Sway Away, you can also just ask them. I've talked to them in the past to, funny enough, get the spring rate on their 1.08" bars for a B-body. They helped also me ID the bars as being theirs (which I bought 2nd hand). Once I provided them with the LCA length, they got right back to me.
                   
                  Last edited: May 9, 2018
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                  • 5.7 hemi

                    5.7 hemi FABO Gold Member FABO Gold Member

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                    Guys, I appreciate all the help that you’ve given me. Thank you very much!
                     
                  • pishta

                    pishta I know I'm right....

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                    72bluNblu, if your LCA is 14" Would that affect the bars rate? (keeping the same tire/rim between the 2 to reduce variables)
                     
                  • 72bluNblu

                    72bluNblu FABO Gold Member FABO Gold Member

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                    First, it's not changing the spring rate of the bar. It's changing the wheel rate.

                    And second, yes. Changing the length of the LCA, ie, the distance from the center of the torsion bar to the lower ball joint, does change the wheel rate.

                    Just look at the calculator. Torsion Bar Wheel Rate Calculator - Sway-A-Way | Racing Technology

                    For example, if you take a 1.08" bar, the same active length of 33.8, and use a 14" LCA instead of a 12.875" one, you get a wheel rate of 226.2 lb/in, instead of 267.4 lb/in like we calculated above with the stock length LCA.
                     
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                    • pishta

                      pishta I know I'm right....

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                      Ok, wheel rate is what I was after, got it.
                       
                    • 67Dart273

                      67Dart273 Well-Known Member

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                      I don't understand your reasoning. If you put a big wide offset on the thing, the car will sag lower. The spring rate will effectively decrease. "Saying" that you are figuring it to the ball joint may make "the math" happy, but the real world effect is it will be softer

                      What you are doing effectively, is putting a pipe extension (wheel offset) on the end of your breaker bar (LCA)
                       
                    • 72bluNblu

                      72bluNblu FABO Gold Member FABO Gold Member

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                      Ok, so apparently I need to clean this up some.

                      So first off, this isn't "my reasoning". There is a standard way to calculate the wheel rate for a torsion bar, and it does not include anything beyond the lower ball joint in a Mopar style suspension. That's what the OP wanted to know, basically we're talking about the advertised wheel rate for that particular torsion bar on an A-body. That's the standard way to calculate the advertised rate.

                      Second, "the math" doesn't need to be "happy". You can calculate anything you want with the math, it doesn't care. It's not "the math's" fault that the standard doesn't include anything beyond the lower ball joint, that's just the standard. The math can calculate the rate at any point you want, if you want to work through the math.

                      And if you look at the disclaimers on the Sway-Away web page I linked with the torsion bar rate calculator, you'll start to understand why there's a standard. Because the actual wheel rate at any given moment depends on a whole bunch of things, and it changes every time the LCA moves up or down. The physics only cares about the horizontal plane for calculating the wheel rate. So, it's not even the length of the LCA that matters, it's only the horizontal component of the distance between the lower ball joint and the torsion bar. That means if you raise or lower the LCA from the point where the ball joint is in horizontal alignment from the torsion bar hex, the wheel rate changes. If you raise the ball joint 2", then the LCA length becomes the hypotenuse of a triangle, and all that matters for the calculation is the horizontal leg. So ride height has an effect on wheel rate, and so does the amount of suspension travel. But it's a small effect. I've calculated the difference over an A-body suspension travel range, you're talking about a few pounds per inch in either direction. Why is the ball joint used? Well, all of this stuff moves in separate arcs. The lower ball joint, the upper ball joint, the spot on the spindles where the wheel bearings ride, the hypothetical center of the axle. All of those parts are in constant motion, and the angle of each part is a factor in the horizontal distance. So if you really want to be technical, you need to consider the entire range of suspension travel, the angle of the spindle and ball joints over the entire range, and then work out the horizontal distance over that entire range. And that will give you the range of wheel rates for a given car, at a given height, with a particular torsion bar and wheel combination. There's probably a suspension program out there that can do it if you input all the suspension points.

                      Or, you could just use the standard. Because the difference over that range is fairly small, and there's really nothing you can do about it. There will always be a range for the wheel rate if you're calculating it exactly over the suspension travel of the car. And unless you're going to change the suspension geometry or range of travel you're not going to alter that range a whole lot, just control the overall rate with your torsion bar choice.

                      You could also use the torsional constant for the bar, because that's not changing. It would be inch-pounds/degree, or some form of force/radians. That doesn't change. But the industry standard is to use the wheel rate, and the standard is to calculate it using the length of the LCA between the center of torsion bar to the center of the ball joint, assuming that the LCA is horizontal (parallel to the ground).
                       
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                      • 5.7 hemi

                        5.7 hemi FABO Gold Member FABO Gold Member

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                        SwayAway is out of the 1.08 bars but will have them in 3-4 weeks.
                         
                      • PST

                        PST Marketing Manager FABO Vendor

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                        Our 1.03" torsion bars are in stock ready to ship if you are interested. We offer a member discount and free shipping within the US 48 States.

                        Thanks
                        James
                         
                      • 5.7 hemi

                        5.7 hemi FABO Gold Member FABO Gold Member

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                        Ordered them from ya James. Thanks!
                         
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