DeTomaso Mailing List: January 98, Message #74
     



From: 	Andy Poling <andy@globalauctions.com>

Subject: Re: sway bars

Date: 	Sat, 3 Jan 1998 02:10:40 +0000



> 	At the risk of discussing the Pantera sway bars to death, I want to ask

> you about your mod of using a smaller than stock front sway bar.  To the

> amateur (me), this sounds a lot like Bob Woodhouse's recommendation, if you

> don't have his super trick adjustable sway bars, to NOT use a front sway

> bar, i.e. remove it.  This seems very unconventional to me and rather

> drastic.  Your recommendation from your years of campaigning the Pantera on

> the autocross tracks is to use a smaller than normal front sway bar.  Can

> you explain how these seemingly "unnatural" fixes improve the Pantera's

> handling?  The May date for the Porsche club at Hallett comes up soon!



I'll try to explain it.  I don't have the Pantera experience that Jack does,

but this is not a Pantera-specific problem or solution.



(sorry - this got pretty long.  If you're impatient or uninterested, just

delete)



I guess it's good to start with an over-simplified version of the basics of

how swaybars work, which will make Jack's backward-sounding recommendation

sound forward after all.  :-)



I like to call swaybars anti-roll bars (because that's what they do - just

like shock absorbers are really dampers), but too often folks lose the "anti"

and think I'm talking about rollbars, so I'll stick with "swaybar" here.



What a swaybar does (in terms of front/rear handling bias) is make _its_ end

of the car work harder to resist body roll (and any other suspension

movement that is not equal on both sides - like many bumps, or Crash Jim

showing off and two-wheeling).  It tries to make the wheels on both sides

move up and down at the same time (relative to the chassis) - and resists

one moving up while the other moves down.  In doing that, it both increases

the workload on the tires at its end and decreases the load on the tires at

the other end of the car.  Also the swaybars have virtually no effect when

the car is traveling straight on a smooth surface.



Since the tires can only handle a finite workload, as you increase the

amount of work they do resisting body roll (and other uneven movements) you

decrease the available traction for acceleration, braking and cornering.

Conversely, as you decrease the load from the swaybar you increase the

available traction for acceleration, braking and cornering.



If the concept of a swaybar bettering traction at the opposite end of the

car blows your mind, then try thinking of it as worsening traction at its

end.  Is that better?  :-) This is proof positive that suspension tuning is

a compromise...



If you want an extreme example of how roll resistance can reduce traction, a

Porsche 911 (and many other cars) with a really stiff front swaybar may lift

the inside front tire clear off the ground when cornering hard.  At that

point, the airborn tire is not capable of contributing to cornering or

braking traction, and the outside tire is heavily loaded, so the available

traction is reduced.



If you have a car with heavy understeer (like a Pantera) you can either put

a bigger swaybar in the rear or a smaller one in the front (or both) to try

to improve traction at the front at the expense of worsening it at the rear.



My Kitty has pretty bad understeer because I've mounted wide tires in the

rear.  I've attempted to tame the understeer with adjustable sway bars by

hardening the rear bar and softening the front bar.  This is an attempt to

get those wide rear tires (which have a surplus of load-handling) to handle

a larger portion of the roll resistance load so that there will be more

traction available at the front for braking and cornering.



I said at the beginning that this was oversimplified.  That's because I

haven't talked at all about how limiting body roll improves the suspension's

performance (which is what the front and rear swaybars, combined, do).

Suffice it to say (in this context) that limiting the suspension to a

narrower range of movement maintains a more consistent suspension geometry

(mostly less camber change), making it's behavior and the tires' behavior

more predictable.  Keeping the car flat also keeps the center of mass (and

thus the center of gravity) from moving relative to the chassis roll center

(imagine a tall truck or bus leaning over as an extreme example).  However,

like overly stiff springs, really stiff swaybars can compromise your ride

quality and prevent your suspension from handling bumps well (keeping the

tires in contact with the road surface).



By the way, in case it's not obvious, a disconnected front swaybar is

equivalent to an infinitely soft front sway bar.  You still have some roll

resistance at the front because the springs and dampers provide some roll

resistance.  The swaybar is just designed to specifically provide roll

resistance and nothing else, so it's more effective.



-Andy



72 Pantera - Rocky         91 Miata - Steve (bionic)            96 A4Q - Rudolf

80 928 - Phantom               97 Miata - Nadia                84 RZ350 - Sting