From: Robert W Smith <rsmith@bfmni.com>
>While researching some info about chassis setups I stumbled on some
>dimensions of anti-roll bars but have no idea how to determine the increase
>in roll resistance of a couple of examples. Any engineers out there that
>can help me out?
>I would like to know the percent increase in the following examples
>assuming all the other factors are equal i.e. material, attachment points
>etc.
I am not an engineer. I seem to remember that all things being equal that
the torsion of a solid bar increases as the fourth power of its diameter.
Thus a bar twice as thick is sixteen times as stiff.
>
>As can be seen the bars are hollow!
The trick with hollow bars is to figure a solid bar of the outside diameter
and subtract from it a solid bar of the inside diameter. As you can
imagine, the hollow bars give you more bounce to the ounce than a solid bar.
>
>Front bar:
>26.6mm diameter, wall thickness 3.5mm vs.
26.6mm OD, 19.6mm ID
If we assume that a bar of 1mm diameter gives a torque resistance of 1
"twistie" (a unit of torque I just made up for convenience, since I don't
know anything else about these bars anyway), a solid bar of 26.6mm would
have a torque resistance of 500,641 twisties. A solid bar of 19.6mm would
have a torque resistance of 144,590 twisties. Therefore your first hollow
front bar has a torque resistance of 356,051 twisties.
>26.6mm diameter, wall thickness 4.0mm
Before we begin, we intuitively expect a stiffer bar because there is more
meat in the thicker wall, and the OD is the same.
26.6mm OD, 18.6 ID.
500,641 - 119,688 = 380,953 twisties.
356,051 100
_______ = ____
380,953 106.994
So your second front bar is 7 percent stiffer than the first one.
>
>Rear bar:
>14.7mm diameter, wall thickness 2.6mm vs.
14.7mm OD, 9.5mm ID
46,695 - 8,145= 38,550 twisties
>15.9 mm diameter, wall thickness 2.6mm
Intuitively stiffer. Same wall, bigger diameter.
15.9mm OD, 10.7 ID
63,913 - 13,108 = 50,805 twisties
38,550 100
______ = ____
50,805 131.789
So your second rear bar is 32 percent stiffer than the first one.
I'm not going to bother to check my arithmetic. There are dozens of real
engineers out there who will have answers for you. See If my conclusions
concur.
Phil Ethier Saint Paul Minnesota USA
1970 Lotus Europa, 1992 Saturn SL2, 1986 Chev Suburban
LOON, MAC
pethier@isd.net http://www.visi.com/mac/
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