[TR] [6pack] Sway Bar Custom Mounts

[Jim Muller]

On 7 Dec 2007 at 7:10, Chuck Arnold wrote:
> Seems to me that the more straight up and down the link is, the less
> lateral stress there is in the components

> On Dec 7, 2007 4:42 AM, Bob Danielson <75TR6 at tr6.danielsonfamily.org> wrote:
> > Any opinions on which way provides better handling?

A few observations, besides the kudos already given.  One more kudo 
from me won't add much.

Check the angles through the range of suspension travel, not just at 
ride height.

The thing is, the supposed need for the A-arm and sway bar to be 
parallel is a simplification.  The A-arm has a longitudinal swing 
axis but the sway bar's swing axis is transverse (plus minimal 
flexing of the bar itself).  As the suspension moves up and down the 
mounting point on the A-arm (the top of the link) moves in an arc as 
viewed from the front, but the outer end of the swar bar (the bottom 
of the link) moves vertically.  At ride height the A-arm isn't quite 
at its furthest out-most point, but at the suspension extremes it 
will have moved inward.  So the angle of the link as viewed from the 
front won't stay at the pretty "vertical" in your picture.  It will 
sit like that most of the time but the sway bar isn't torqued unless 
there is differential suspension travel between the wheels.  Minor 
suspension movement upward will move the link's upper end outward a 
little.  Major movement upward and any movement downward will move 
the upper end inward.  I'm guessing you still want the "flipped-over" 
vertical arrangement, but it is worth checking.  From a geometry 
standpoint a big improvement is simply having a longer link, which 
means less angle change as the suspension goes up and down, and less 
flexing of the bushings too.

Also the transfer of movement from wheel to sway bar depends on the 
geometry.  The top of the link will move more if it is further out on 
the A-arm.  This means the bar will be torqued more, thus equivalent 
to a stiffer bar.  The geometry between upper and lower link ends 
will change during the suspension travel and for the two different 
mounting arrangements it will change differently.  But it's hard to 
say whether one is better or if the difference is even signficant.

A final observation is that all the vertical force on your link will 
be born as flex on a planar surface.  There is no vertical backing 
edge to convert that flex to shear.  Perhaps your bracket is robust 
enough that it doesn't matter, but you should check it over time for 
fatigue.  Heaven forbid that in another 3000 miles you have to do all 
this again.

-- 
Jim Muller
jimmuller at rcn.com
'80 Spitfire, '70 GT6+