Stabilizer bar upgrades SUMMARY - by request...

["Aaron Bohnen" <bohnen@xxxxxxxxxxxxxxxx>]

Hi everyone (again), 

Well, I've gotten lots of 'feedback' on my stabilizer bar rantings from
yesterday. Mostly seems it was pretty well received, some said too much 
babbling, not enough focus on what it all means. Some asked for a boiled 
down version with the basic take-it-home type results.

So, by request, here's the summary, in short, abbreviated, pared down, 
minimized, etc... They are listed as RESULT 1 and RESULT 2 below if the 
reasons why they come about doesn't really interest you much - just scroll 
down a little. I won't be offended. Really. :>

Here's the three basic ideas:

I. Stabilizer bar torsional stiffness is governed by three parameters. The 
stiffness of a solid stabilizer bar is:

 - proportional to the diameter (raised to the fourth power)
 - proportional to the shear modulus of the bar material (ie: how resistant 
   the material is it to shearing actions)
 - inversely proportional to the length (ie: longer bars are easier to 
   twist)  

II. Therefore, for a given length and material the stiffness of the torsion 
    bar is governed by the diameter, raised to the fourth power.

III. These facts (I & II above) have two important results. They are:

RESULT 1:

Changing a stabilizer bar's diameter by a small fraction can make a 
dramatic difference in the torsional stiffness. ie: 1 or 2 mm larger 
diameter can lead to very noticeable effects, namely reduced body lean in 
cornering, etc. For example: a 15.5 mm bar is 50.2% torsionally stiffer 
than a 14 mm bar.

RESULT 2:

The result of a millimetre or two increase in diameter is much more 
dramatic when the original bar is small. If you already have big-boy 
torsion bars you will have to increase their diameters more to achieve the 
same fractional increase in stiffness. In other words, small bars can be 
easily upgraded by using slightly larger bars. Large bars need to be 
upgraded to quite-a-bit-larger bars in order to achieve the same 
fractional increase.

So that's it. The whole story on stabilizer bar torsional stiffness.

We could go into the resulting forces and their relationship to the 
stiffness, length of end levers, etc. etc. but that's really not too 
applicable for our purposes.

OK, that's it.

Aaron

p.s. - all those of you who responded in various ways about Hooters girls, 
stabilizer bars, etc. must have missed the main thrust (so to speak) of my 
postscript. The point is that the bending and torsional stiffnesses of 
a cylindrical solid bar are proportional to the fourth power of the 
diameter. And the AXIAL COMPRESSIVE OR TENSILE stiffness is proportional 
only to the second power. So, like I said - it's one of those things where 
the big boys win, but not by as much as they'd like to think they do. 
The only thing left to say about this is that if you are in the position 
where the torsional stiffness of a cylindrical bar is of any consequence to 
your love life I don't want to know anything at all about it. All that 
makes me think is "Indian Rope Burn!"
___________________________________________________________
Aaron Bohnen                     email: bohnen@domain.elided
- -Ph.D. Student, Civil Engineering Department, U.B.C.
- -Technicraft Engineering Services

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