Date: Tue Jul 26 23:20:57 1994   
From: John De Armond
Subject: Re: Comments re: suspension changes.

>>They also said that strut tie bars aren't worth the metal they're made
>>of, at least for racing purposes.  They recommend the bars that are
>>shaped like a long, skinny "K", unlike the ones sold by most vendors with
>>a single bar.  With the "K" design the strut towers do the job of 
>>preventing the strut towers from bowing in or out yet still allow for 
>>them to flex independently.  This  design makes for less understeer than 
>>the run-of-the-mill strut bars.  Any comments on that one?
>
>I do not see why the strut towers need to flex at all. Ideally speaking
>they should be absolutely rigid. 

This is not necessarily true.  I know that a few big names such as 
Carrol Smith advocate absolutely rigid chassis but that view is 
certainly not universally held.  Strict segregation of function is
not necessarily the best setup.  Spring designed into the chassis
at the right points can augment the suspension function and can give
some desireable dynamic changes in geometry.  The classic example of
this is the racing kart which has no suspension but has significant
chassis flex that serves as suspension.  These things, of course,
corner harder than anything else available to us mortals.

My point is not to endorse the K-bar.  I have no idea whether it works
because I've not used it.  I just want to suggest that it not
be dismissed out of hand.

John

Date: Fri Jul 29 11:34:17 1994   
From: John De Armond
Subject: Re: Re[2]: Comments re: suspension changes. 

emory!oasys.dt.navy.mil!paraska (Pete Paraska)

>John, I think I might have to go with Zane on this one.  (Jeesh, I'm
>disagreeing with John?  _I_ can't even believe it. :)
>
>John's point is well taken as far as carts go - the chassis IS the
>suspension.  But I'll go along with Zane, Carroll Smith, etc. on the
>part about having a stiff chassis on a car - for a number of reasons:
>

But what you cited in the deleted material are specific exceptions to a
general guideline.  I vigorously oppose recipe racing ("weld a strut here,
drill a hole there, add three mothballs to the gastank, rub a green
magic marker around your CD and you'll be faster than anyone on the 
track").  I think it important to understand what one is trying
to achieve.  While a striving for a stiff chassis is a good general
guideline, it is important to understand when there may be exceptions.
I've seen enough instances on both cars and motorcycles where stiffening
a chassis hurt lap times and that is what ultimately matters - going
faster.  For example, if you stiffen the chassis so much that the
harshness becomes distracting, you will become slower.  I developed
a theory in my motorcycle days after watching slo-mo films of many
riders, that one can maintain control as long as the sudden head
motion stays under 6".  Most people start to lose control when
the head is jarred repeatedly more than 6".  Pay attention to a 
professional motocross rider and watch how stable his head stays
and then watch the slo-mo of someone in an incipient crash.
I have more than once slowed my rider down by "improving" the 
chassis so that the rider received more harshness.   I also believe
there is a total limit to how much sensory input the brain can
process.  When you eat up some of that bandwidth receiving and 
reflexively reacting to vibration, jolts and harshness, you have
less bandwidth available to maintain control.  I KNOW that is the
case with me on a motorcycle.  There is a point where the sensory
input gets so great I just can't do anything else.  I believe
the same thing holds true for cars.  I know that when I made 
certain "improvements" to my Z, my speeds went down.  One thing
I REALLY disliked was the strut tower brace.  It made the
steering much harsher.  Or consider the instance where a bit of chassis
flex makes the car transition from understeer to mild oversteer
just as the front end is pushing out.  Desirable in many instances.

I'm not trying to talk anyone out of doing anything.  I'm opposing 
recipe racing, also known as "bolt'n'pray".  Make one change at a
time and objectively evaluate it.  If it doesn't work, regardless
of the conventional wisdom, take it out.

You may now have your soapbox back :-)

John

Date: Wed Aug 3 21:59:29 1994   
From: John De Armond
Subject: Re: Re[2]: Comments re: suspension changes. 

>>I know that when I made 
>>certain "improvements" to my Z, my speeds went down.  One thing
>>I REALLY disliked was the strut tower brace.  It made the
>>steering much harsher.
>
>I haven't done the strut tower before, but I'll keep that in mind.  To give 
>me an idea of the harshness you experienced with it, could you tell us what 
>else you've stiffened beyond stock in the front suspension/chassis of your 
>Z?  I know some Z people don't like the added harshness of just one of the 
>following:
> Aluminum/Delrin T/C kit, Nylon steering coupler, camber plates w/o any rubber.

I did all the usual stuff that you mentioned above.  I've pulled the 
metal steering coupler out and reinstalled the hard rubber one and I'm about
to pull my rigid mounts on the steering rack.  These are the rigid mounts
I described a year or so ago that I cast in place using epoxy and 
fiberglass - even more rigid than delrin.  

I'm really enjoying the move in some racing circles back to some
"luxuries".  Power steering is now de rigeur for NASCAR and most other
dirt racing.  Now I'm seeing a move toward air conditioning the 
driver's suit and the air he breathes.  What next, padded steering
wheels and carpet? :-)

Totally un-z-related tangent:  I saw the new Chevy Impala today up
close and personal for the first time.  Damn, I want one.  Ooohh, does
that mean I'm turning into an old fart?

John