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Re: Coupe GT Anti-sway bar for rear

Paul R Anderson wrote:
> Many questions concerning anti-sway bar diameters can be addressed
> by the following statements.
> An anti-sway bar's torsional stiffness (resistance to twist) is directly
> proportional to its cross sectional area.

Almost. It's proportional to the square of the area, or to the diameter

raised to the fourth power.

The deflection in degrees is given by:

deflection (twist, deg) = 584 * TORQUE (inch-pounds) * LENGTH (as Paul
said, the twisting part of the beam, inches) / DIAMETER^4
(DIAMETER*DIAMETER*DIAMETER*DIAMETER, inches) / G (torsional modulus,
for all steels 11,500,000 pounds/square inch)

To determine the TORQUE, you need a load, and the load's distance from
the rotational axis of the bar (assuming the link bolt is at a right
angle to the bar's lever arm). Multiply these two together to get the
torque. eg, 50 lb (load) * 7 in (distance) = 350 in-lb. DO NOT double
this number just because you're also twisting the other end of the bar.

> The bar's actual working
> stiffness is also dependent on the length of the lever arm (the
> perpendicular distance from the end of the bar to the torsional axis
> of the bar.  If the arms are twice as long, it will cut the working
> stiffness of the bar in half.  Also to be taken into account is the
> material the bar is made of and whether it is tubular or solid.
> On FWD cars with torsion (T-beam) rear axles such as the
> VW Rabbit/Scirocco/Quantum, and, I believe, the 4000, you already
> have, in essence, an anti-sway bar.  It is T-shaped instead of
> round.  The rear bar adds to the effect of the rear axle beam.

The 4000 ('86, anyway) has an inverted "U" shaped channel, with a round
bar in the bottom of the U (closest to the sky when installed). Chrysler
has copied this design on about 50B minivans, though Audi sure didn't
invent it . . .

One method of stiffening the front (dunno why on a typical FWD) is to
shorten or lengthen one of the AR-bar link bolts. This pre-loads the
bar, kinda like a Charlie washer for the pressurized weenies (hoping to
become a tubular meat-like product myself in the spring ;-) 

> . Addco makes a 1" bar for the front, and the 3/4" rear
> >bar,
> >which seems kind of arse-backwards to me for a fwd car. Perhaps the
> >small diameter of the rear bar is intended to allow for the axle to
> >flex
> >as necessary. Actually, I never knew the rear axle had any movement
> >other than up/down!
> Even though Addco bars are relatively cheap, they seem to work
> well in pairs.  I'd probably go for it.  Try J.C. Whitney for best price.
> That's the only place I've ever bought an Addco from.
> Paul Anderson, Cheyenne, WY  Private email:AndersonPaul@juno.com

NOT A SUSPENSION EXPERT, just a mech eng
'87 4kq, has awful body roll but tracks good enough to PAX 1st
'86 4ks, needs rollers fitted to door handles
'64 Falcon Sprint conv, V-8 & 4 speed, who needs to turn???
Boise, ID, USA