Ok, so its probably necessary at this point to discuss a little about suspension design, We’ll start with solid rear axle suspensions because that’s what most of us have and there are many designs, and so much confusion about the how and why for each setup. Each type of suspension has its own inherent pros and cons, and each style can be analyzed and discussed enough to write an entire book, so this will be a brief overview of each explaining its components and uses. On its most basic level a suspension suspends the vehicle above the tires (maybe that’s where the name comes from), absorbs the energy of bumps etc, and locates the tires.
Lets start with the one we are all most familiar with…the oxcart suspension that comes on the rear of the beloved Syclone and Typhoon. Leaf springs are cheap easy old school technology, they require no adjustment, very little maintenance, and on a rudimentary level get the basic job done. In this system there are stacked springs(usually steel strips) bolted directly to the axle which absorb bumps and load as well as control movement and position the axle. Throw on a set of shocks to dampen the movement and you”re ready to go. Cheap, simple. and reliable. This is why they are still in use today on trucks for example where there is less concern with proper handling and more focus on economy and load capacity.
The next setup you’re probably pretty familiar with is the four link. A four link is four links or bars attached to the rear end connected it to the frame of the vehicle. This can be done one of two ways, parallel or triangulated. In a parallel four link, all four bars are mounted in parallel to the each other along the length of the vehicle, the lower links locate the axle front to back on the vehicle and the upper bars control pinion angle and axle rotation. The links do not control side to side movement, so an extra device is needed to hold the axle under the vehicle countering lateral forces.This is done using a panhard bar, watts link, or diagonal link. This type of suspension is prevalent on drag cars because its design has inherent bind issues when used for anything more than straight line acceleration. The triangulated four link uses the same style two parallel lower bars to locate the axle front to back, but the two upper arms are angled in (big surprise here) a triangulated configuration. These links are usually positioned on an angle between 30 and 45 degrees from parallel to the lower bars. This is the system found on gm G bodies and the Fox Mustang. The triangulated upper bars act to locate the axle side to side and counteract lateral force essentially eliminating the need for the watts or panhard bar. The triangulated setup still experiences bind, but much less than a parallel, and it actually uses a bit of bind to maintain lateral control of the axle. Throw in springs and dampers/shocks. and you’re ready to ride. Subtle tweaks of the geometry of the bars allow changes in traction, ride quality and braking making the system much more effective in a variety of road conditions and use. The oems like this triangulated packaging because it offers good ride and handling with only slightly more cost than the leaf spring system
The third solid axle suspension is the three link. From the side view, the 3 link and 4 link operate the same and things such as instant center, anti-squat, anti-dive, etc. With only 3 links the binding in other designs is almost eliminated. With only 3 links we require a locating device such as panhard, watts link, etc. As with all suspensions upsides and downsides exist. Downside of the 3 link besides the requirement for locating bar, is that the upper bar has twice the force/stress as an upper bar in a 4 link. Being this is the case that bar must be designed and sized properly in order to handle that stress.
Other rear designs available beyond these 3 include truck arm, torque arm, and many other less common designs. As with everything 1 size does not fit all, and 1 is not superior in all areas to the rest. Cost, packaging, type of driving, all play a part in the selection of which rear. JSM’s goal when designing any kit is to drastically improve from what the factory selected, while also providing great value, packaging, and appeal. Stay tuned for more, and let us know if these are helpful.