Lanciana: DECEMBER 1990 - 24

Scorpion Handling John Stuckey

I had a head start on this project because of the hard work of John Keppelman. I had once mentioned to John my intuitive suspicion that Scorpions had a serious flaw in their front geometry in the form of dramatic bump steer. He subsequently researched this on his own car and devised corrective measures that he has documented elsewhere. After affecting the Keppelman Kure for bump steer I took a look at the rest of the suspension. The next most important improvement was obvious; lower ride height. Why the same people who gave us Stratos 246, X- I9 etc.. thought that this particular mid-engine sporster needed eight inches of ground clearance I will never comprehend. Comparing the stance of the stock Scorpion to that of the aforementioned machines? it was apparent that major work was in order as the front end needed to come down at least two inches.

I started by substituting X-1/9 struts for the original front units. These have the hub carrier mounting bracket higher up on the body, so that normal wheel travel could he preserved. Unfortunately the spring seat interferes with the Beta wheels and 195/60-14 tires fitted to the subject car. Cutting the spring platform loose and rewelding it 3/4 inch higher on the tube called for disassembly of the struts. Since the newer X-1/9 (and Scorpion) struts are not dismantlable I chose Koni complete strut replacements. These have damping rates much stiffer than the stock Scorpion struts. It was necessary to move the rubber bottoming stop to allow use of our relocated suspension travel. I determined that shortening the welded sleeve securing the bump stop to the upper spring seat to l/2 inch would give the desired results. I shortened the Scorpion springs by 1-1/2 coils at the bottom, reshaping the final coil to approximate the shape of that cut off. This lowered the car by about 2 inches, but at full compression, coil bind was reached a bit before full shock travel. I remedied this by removing 1/2 coil from the top of the spring with no reshaping. This eliminated coil bind. lowered the car a further half inch, and left a shape which registered adequately on the spring, mount.

I decided to lower the rear of the car only about an inch so that a nose-down attitude would replace the original nose-up stance. I hoped that this would reduce aerodynamic lift and improve the high speed handling. It also looked a lot better. Struts for an X1/9 again seemed like the solution, as they are an inch shorter than a Scorpion's. Unfortunately, for reasons that Koni's technical department cannot explain their rear struts for a late model Xl/9 are one inch longer than stock. Therefore. we were were forced to settle for Scorpion struts and accept the reduced travel. The springs were shortened by one coil and reshaped to affect the lowering. At this point the car was tremendously improved. Front adhesion on braking was almost unbelievably better with the diminished bump steer. Front cornering adhesion was greatly improved by the increased negative camber and reduced weight transfer resulting from lowering and stiffening the front end. All that remained in my esti- mation was to improve the steering feel.

The principle component of steering feel or feedback is the force generated by the trail designed into the suspension geometry. This is the dimension by which the center of the tire contact patch "trails" the intersection of the steering axis with the road surface. For a given design, increasing the caster increases the trail, so this was the first area for us to attack. This particular car had a caster angle of 3-l/2 degrees before modification. This was reduced to 2-1/2 degrees by the change in the car's attitude Lancia recommend 6 degrees, which seems prudent for such a light front end. It was obvious that removal of all of the adjustment shims from the tension rods would not achieve nearly 6 degrees, so I decided to offset the bushings at the front of the rods. I reasoned that it was foolish to have fore and aft compliance of the wheels equal, as the probability of encountering bumps in the road at a high rate of speed whilst traveling backwards is rather small. (If such should become the case. small additional ride harshness would most certainly not be the foremost concern.) To this end I selected three new bushings and cut one of them- in half. The half bushings were installed on the rear of the tension rod mounting brackets with the whole bushings on the front. With all of the spacers removed this yielded 6-1/2 degrees caster on both sides of the car. An attractive by-product of this modification was that the bushings were not compressed nearly to the limit of their compliance on installation. This allows some rearward deflection of the front wheels on bumps, greatly improving the ride. The final step was to remedy the excessive steering friction of this particular car caused by over-shimming of the steering rack by the good folks at TRW. This done, the car was marvelous: good stability, decent ride, sharp turn-in, and linear steering effort telegraphing front tire loading accurately.

Nearly every Scorpion which I have seen in the shop has had fatigue cracks around the mounting plates for the front suspension tension rod brackets. When well developed. these lead to excessive flexing of the body and unpredictable suspension geometry. To remedy this on a recent project car I fabricated a truss to convert the bending loads on the body at this point into straight compression loads. The accompanying drawing and photo illustrate the simple arrangement. Enlarging the existing drains in the trunk floor with a one inch hole saw gives access to the bolts securing the rear of the longitudinal strut to the drain holes in the bottom of the hollow frame member. Be sure to drill a couple of new drain holes at the lowest points of the crossmembers to replace those plugged by the bolts. The dimensions on the drawing were taken from this particular car, but the truss really should be built in place