DeTomaso Mailing List: January 98, Message #145
     



From: 	MikeLDrew@aol.com

Subject: Sway Bars [part 3]

Date: 	Tue, 6 Jan 1998 00:33:54 +0000



[The third and final part of this discussion]



Larry Stock had a new motor built after losing the mostly-stock original at

Las Vegas '92 to a spun rod bearing.  We think this occurred due to Larry

using Goodyear race slicks with a stock oiling system.  The new motor is

substantially stronger than before, so he really wanted to maximize the

handling of his now not-so-stock Pantera.  A 100-ft diameter skidpad was laid

out in a lot across from his business.  The surface was an average

asphalt-bonded stone, about five years old.  A G-analyst from Valentine

Research was solidly mounted in his car per directions, on the console back

in the knick-knack tray.  This position seemed to be very close to the center

of balance of the car.  The good folks at Pantera Performance Center in

Denver, Colorado, provided a variety of swaybars for us to test and compare.



The car is a '72 Pantera, with stock suspension components except for Carello

shocks, running 15x8 front and 15x10 rear aftermarket wheels with Pirelli

P7's in the standard 225/50-15 and 285-50/15 sizes.  The wheels had stock

offset and required no flares or spacers to fit.  The shocks were adjustable,

but were not optimized for the various swaybar combinations used.  To obtain

the best handling characteristics, the ride was lowered, and the front end

was set for 1/8" toe-out and -1.5x camber.  



In Test 1, the car used stock front and rear swaybars; 0.845" front, .750

rear.  It was able to maintain 0.79 g's on the described skidpad.



Test 2:  the rear bar was exchanged for a .875" unit.  This is the so-called

GTS or Group 3 swaybar setup, recommended when running larger-than-stock rear

wheels/tires.  The car was now able to maintain 0.93 g's with this single

change.  Since the bar change took over half an hour, the tires had obviously

cooled back down to ambient before starting Test 2.



Test 3:  figuring that if some is good, more is better, the front bar was

exchanged for a 1.0" bar, while the rear stayed at .875".  Now, the car could

only hold 0.91 g's - a slight step backwards from Test 2.



Test 4:  the rear bar was increased to 1.0" along with the 1.0" front bar

from Test 3.  The car could only hold 0.89 g's while in this configuration, a

further step backwards.  This is especially confusing, since it is the

configuration used by some for road racing, and was recommended by the folks

at Pantera Performance as the "killer setup".  However, they have used this

combination mostly on cars with 15x10 front and 15x13 rear wheels, i.e. Group

4 or GT-5 cars, which not only have much more rubber on the ground, but

possess a much wider track, as well.  



For Test 5,  the car was returned to the test 2 configuration and Larry's

favorite gumball race tires were mounted.  In studying the printouts from the

G-analyst for this Test, it can be seen that the car now turns left at 1.10

g's and turns right at 1.25 g's.  Left turns are smooth and predictable while

the right turn segment was ragged and obviously right on (or over) the edge.

 With cornering power like this, it is easy to see why Larry had oiling

problems on the racetrack.  The oil in the stock pan rode right up the side,

away from the pump pickup.  After a few episodes of the pump sucking air,

there were no bearings left!



Most people can turn to the left faster than to the right, simply because in

a hard left turn, the whole car is pivoting around the driver's seat.  During

right turns, the driver's position is also pivoting with the car, so his

point of reference is constantly changing during the turn.  This introduces

another variable or two which destabilizes the driver's reference points.

 The result is, you tend to slow down (unless you are in a 'banzai' mode, but

this is difficult to maintain for long, and often results in a trip to the

tules).



So why didn't the progressivly stiffer bars give progressivly better

performance?  The answer probably lies not with the swaybar or suspension,

but with the chassis itself.  Noted engineer Kevin Cameron recently wrote a

piece on the relationships between frame and suspension stiffness in

motorcycles, and used automobiles to explain his theories.  He described the

fact that any suspension is three springs in series - first is the tire,

deflecting to absorb the smallest bumps; next is the suspension spring and

associated components; behind that is the flexibility of the chassis itself,

being deflected by the forces transmitted through the suspension.



Stock car racers learned years ago that there is no point in putting stiffer

suspension on a chassis too weak to support it.  As a bump pushes the wheel

up, the spring, shock absorber and sway bar resist the motion, passing on the

force to that corner of the vehicle, which bends upward as well.  Once the

bump has passed, the shock absorber prevents the wheel from snapping back,

rebounding off the pavement again, and continuing to oscillate.  But the

chassis has no shock absorber to damp its motion so it continues to vibrate

up and down.  This continuing motion can be just as disturbing to tire grip

as running without a shock absorber.  The correct response would be to

stiffen the chassis (notoriously weak in the Pantera, particularly in the

rear, although extrordinarily strong by street-car standards), to force more

of the bending to occur in the suspension, less in the chassis.  However,

this would require major re-engineering of the chassis, and the costs of the

design and fabrication would be prohibitive to all but the most die-hard

Pantera crazies.



It seems that most Pantera owners would be well-served by changing their rear

bar to a .875" unit and leaving the front bar alone, particularly if the

tires have been upgraded to at least 1980's-spec sizes.  Besides increasing

the overall cornering abilities of the car, the driving characteristics will

likely become much more neutral, without the plowing of the front end that

Pantera owners have endured for decades.  However, such a setup will create

the need for circumspection when driving, for once the car reaches its

(higher) limit, it will probably be much less forgiving!

--------------



Note:  This data was collected in 1993, but the thoughts behind it are sound.

 I realize that serious chassis gurus like Gary with his super-sexy data

acquisition devices, etc. might be able to improve on these thoughts, or view

them as an oversimplification of an admittedly dynamic situation.  But for

95% of us, this here about covers it! :>)



Mike