THE MAKING OF A GOOD LEAF SPRING SUSPENSION: Achieving a smooth, nice riding and handling leaf spring suspended vehicle is very simple, provided some basic rules are followed. Just four areas make the difference between a good leaf spring suspension and a bad one.
1) Multi-leaf springs. Only with multi-leaf springs can the correct spring design be achieved. Springs support weight, absorb road shock and set vehicle height. With multi-leaf springs, critical design factors such as stepping, rate, load and spring height can be fine-tuned. Mono-leaf springs seem to be the fad among street rodders, however, due to production methods; mono-leafs must be made in high volumes. Therefore, they are made with only one rate. Because no two cars are built the same, vehicle weights vary and consistent ride qualities cannot be achieved. Equally important is ride height. Again, due to production methods, monos are built with the same free height. The only way to adjust ride height is by the use of blocks. Safety is another factor, should a multi-leaf spring break a leaf, including the main plate, there are other leaves to support the vehicle. Monos do not offer this protection.
2) End type. Square ends, or constant thickness ends are great for trucks. Diamond pointed or trimmed ends are great for better riding trucks. However, for the smoothest riding spring, the ends must be tapered. Tapered leaf ends moves the friction area away from the leaf ends and spreads it over a much larger area, resulting in less force needed to flex the spring.
3) Blocks. The use of blocks to either lower or raise a vehicle is the leading cause of axle windup and poor vehicle handling. The most secure suspension is one where an imaginary line drawn between the spring eyes is as close to the axle seat as possible. The use of blocks takes this line away from the axle seat resulting in a fulcrum point. This leverage point allows the axle to pivot around the spring seat causing axle windup and handling problems.
4) Shackle angle. As a spring flexes, it grows in length. The purpose of a shackle is to allow for this growth. Although spring rates are fixed by its makeup, the amount of force required to move a spring can be greatly increased by incorrect shackle angle. Any shackle angle exceeding 15 degrees is too great. Installing a Panhard Bar on straight axle street rods with a transverse spring will allow the spring to be lengthened so the shackle angle can be at 15 degrees or less. The resulting improvement in ride can be dramatic.
FOR ALL SUSPENSIONS: No matter what type suspension your street rod has, leaf spring, traditional coil spring, torsion bar, air, or coil-over, the importance of a high quality shock cannot be understated. Shocks are the final touch that completes the ride quality of all vehicles. The difference between an “OK” ride and a smooth, comfortable ride can be attributed to the shocks. The only function of any shock is to control the springs’ energy. Non-adjustable shocks lock you into accepting the ride quality that the shock is limited to. Choose by application, not by length. Adjustable shocks allow you to fine-tune the amount of control you desire, optimizing ride quality. With the technology in springs and shocks available today there is no reason to have your street rod ride like it is stuck in the 50’s. All street rods have the ability to ride and handle like a current production vehicle.
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