Strength and Durability Testing
Matt Jones: Strength, durability, and performance are measured in two ways at Art Morrison Enterprises. The first is computer simulation, and the second is real-world testing. Before prototype production begins, designs are validated via Finite Element Analysis (FEA) and computer suspension simulation. Each part is checked for strength and durability, and we remove as much excess bulk as possible. Prototype samples can then be checked for stiffness using real-world methods, and our in-house vehicles tell us what the vehicle will do on public roads and perhaps what may need to be adjusted. The benefit of building chassis for over 35 years is the wealth of knowledge that accumulates in chassis design. Every design has been proven hundreds if not thousands of times in the past, and knowing which designs do and don’t work allow us to confidently work toward the right direction.
Craig Morrison: All the chassis built at Art Morrison utilize framerails that are manufactured in-house. For our Tri-Five frames, we start with 2x4x0.012-inch wall tubing, and then cut the ’rail sections to length. From there they are bent, utilizing one of our two mandrel benders. A mandrel bender inserts a die into the center of the tube to support it on the inside while bending it to prevent the tubing from wrinkling. When the ’rails are bent, they are trimmed to a final length and then loaded onto the jig table. The brackets are laser-cut and formed by one of our suppliers, and bolted onto a jig table. Once the chassis is completely loaded, the welding begins. A typical chassis requires 8-10 hours of welding to join everything together. From there, the chassis is pulled out of the table and all the welds are inspected for completeness. Afterward, any weld spatter is removed.
: One of the biggest drawbacks of building a suspension around a stock chassis is that significant changes to the camber curves, caster, and roll center can’t be made without moving the stock suspension pickup points. This is particularly true with cars like the ’55-57 Chevy, since suspension technology has advanced quite a bit since they were originally designed. The luxury of a ground-up redesign when using a new frame design eliminates many of these restrictions. Generally, the overall aggressiveness of the suspension will be based on customer preference, and every aspect of the chassis design is a balancing act. The steering knuckle design is determined by what size wheels the customer will typically run. For example, Tri-Five owners don’t usually run 20-inch wheels like the typical Pro Touring muscle car, so C6 Corvette knuckles aren’t a good idea in these applications. Control arm shapes are contoured for tire clearance, and brackets and crossmembers are shaped to ensure adequate engine clearance. Likewise, the availability of different antiroll bar materials will somewhat determine the roll center location. Higher roll centers will effectively increase roll stiffness and vice versa.
Furthermore, spring availability will have an affect on motion ratio requirements and roll gradientsor body rolland wheel rates are determined by the preferences of the typical customer. Lastly, the steering rack will be placed in the optimum location and checked for clearance with all engines that may be used in the chassis. Multiple iterations of a chassis are usually required for each new suspension design, as one change creates a domino effect that leads to other changes. For example, if the engine requires a U-shaped antiroll bar for harmonic balancer clearance, the resulting roll rate change must be accounted for to see if the roll center height must be adjusted again. At that point, the steering rack will be relocated for the optimum bump curve and then rechecked for clearance. The steering rack relocation will also require rechecking tie rod to antiroll bar link interference. In the end, various parts of the suspension will be redesigned several times until everything is satisfactory.
Matt Jones: Reducing unsprung weight is vital in almost all aspects of performance, especially in vehicles that use live-rear axles. Higher unsprung weight will have a negative affect in both handling and ride quality, the two most important aspects in chassis performance. To put it into perspective, modern independent rear suspensions using aluminum components will typically have about 295 pounds of unsprung weight, while live-axle systems weigh in at about 385 pounds. That represents a 30 percent increase in unsprung weight. Consequently, it’s very important to make the suspension as light as possible in both the front and rear. Lighter suspension components can get away with a lower spring rate, which then leads to lighter damper valving, both of which give a significant increase in ride quality. CHP