RE: [DML] RE: Toby TAB alternative

["mgutkowski@xxxx" <webmaster@xxxx>]

Hi Darryl (and all)

I've been pondering this issue that Darren has raised and have a few
thoughts to share. Firstly I want to point out that these are just my own
musings and not based on any particular qualifications or knowledge -
merely a few questions.

Firstly, the Pearce Design website has photos of their new trailing arm
mounts here

http://www.pearce-design.com/PFImprovements.html

Now, we don't _really_ know all the design work that went into the
DeLorean's chassis at Lotus, and to be frank, what we have is a really
quite complex system. The more I think about all the movements involved,
the more I get a headache. We know Lotus spent a great deal of time
engineering the rear suspension to take account of that massive chunk of
aluminium we call an engine, and its relatively high mounting position. The
rear wheels do not just go up and down, but castor and camber angles change
dependant on body roll because of the interaction of the trailing arm and
unequal wishbones - all of which go towards keeping that heavy back end
under control.

But here's a very basic observation: The original mount allows the trailing
arm to move up and down in the axis perpendicular to that of the trailing
arm. The Pearce Design system allows it to move up and down in the axis
perpendicular to the backbone.

I could be completely wrong, or this could come well within what us
engineers call "near enough to make no difference". However I can't help
but wonder why a company as experienced (possibly THE most experienced) as
Lotus would make such an obvious boo-boo as have a critical bolt in a
"single shear" application (is that right, Toby?) when supporting it at
both ends is so easy to achieve. It seems to me that it's been done that
way for a reason, and to muck about with it is to potentially adversely
alter the way the car was designed to handle. 

I sometimes wonder if adjustable lower control arms are a good idea for the
same reason.

Best Wishes

Martin
#1458
#4426

Original Message:
-----------------
From: Darryl Tinnerstet darryl@xxxx

A word of caution here - think about the geometry of the rear suspension. 
The trailing arm twists as it moves up and down, due to the upper and lower
links being different length. This is what keeps the "contact patch" of
the tire in the same spot as it moves up and down, and is the main reason
for the rubber bushing the TAB goes through. Any bracket that firmly
captures the outer end of the bolt is going to force the arm itself to
twist, not something you want to do. If the bracket is only intended to
capture the arm if the bolt fails that would be different, but I doubt
that's the case. 1963-1983 Corvettes put the rubber bushing in the end of
the arm and supported the bolt at both ends, but our setup is unfortunately
inferior to that. And this is precisely why Toby chose to engineer a super
bolt that would not bend or break.  



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