Understanding Five Link Suspension
By now, every enthusiast in the world should know that five links that hold your rear axle in place are critical to any form of automotive sport.
Where & why are these bars connected to you're rear axle? Five link setups are native to the AE86 and come on all models/years. The key roles they play in the dynamics of rear suspension travel are; axle twist and drive/forward propel and horizontal articulation. The images below will plainly show the links location.
How exactly do these bars work?
First, we will address only the semi-trailing arms or the four links. The benefits of a 4-link setup are; when the bars are equal or near-equal (the case of the ae86) length, and the mounting points are similar. The range of vertical motion for the axle is very unrestricted. The key benefit is that each pair of links is independent of the other, with this design the axle can move or rotate freely. Now, if you are still confused, lets put it in real-world applications.
This design allows for when one wheel has to travel in a different vertical path than the other wheel (over a speed bump). The wheel that isn’t traversing the obstical is generally, unaffected and stays in contact with the ground. During a race environment, imagine a sharp right hand turn, The body rolls to the outside of the turn (left), decreasing the distance between the frame/body on the left side, thus increasing the distance between the frame/body on the right hand side. The 4-link design, with it's independent links, allow for stable traction and independent axle/chassis movement on the right and left sides. In effect, the axle can articulate fairly freely compared to other suspension designs, such as leaf spring.
Now that you can understand how the 4 links design works to aid in axle twist, lets go over how it helps with forward propel. This concept is a little harder to grasp with just a worded explanation so below is a diagram of the effects that will be described.
Rear 4-link design during a STOCK application allows for steady rear tire traction and control. This happens by a transfer of force. When the clutch is applied and the engine propels the drive train, it spins the wheels and creates a forward propel. This energy is transferred into the angled links from the axle because the wheels in effect are driving the axle under the car. With this momentum the links drive into the chassis of the car and the chassis creates a reciprocating downward force onto the axle and thusly the tire, creating… traction!
The final component of this system, the 5th link;
With the five link suspension design the four main links control the forward drive and vertical articulation. The axle needs something to prevent it from sliding horizontally. This is where the 5th link steps in. For example, when turning a corner hard on a race track or drifting. The 5th link keeps the axle from shifting left or right. When force exerted towards one side, the bar will drive into the chassis or the axle, thusly keeping the axle in place and preventing the axle from shifting or swaying from side to side.
So why upgrade? A few reasons for upgrading, the main being adjust ability. Once we lower the AE86s chassis to the suspension, we find that we have thrown the stock rod angles into totally different positions. In fact, its safe to assume the lower you go, the more your rear axle will be pushed to one side. The axle will be driven to the left side (mounted to the body on the right) because of the rod length, so as we lower the car we need to make the bar shorter and shorter. Another reason to upgrade is for strength increases, some bars that are sold are very strong and made from very dense metals with very rigid joints. Some bars have an overall lighter weight, stronger links or stiffer bushings.
Traction Brackets & Lowering
While on the subject of rear links, you cannot ignore traction brackets. These should actually be called ‘angle correction brackets’ because they don’t create any benefit over the stock setting… they put the 4 links back to stock! Well… not exactly but close. The whole reason for getting traction brackets is simply to counter act the negative effects on your four links in the process of lowering your car.
As you can imagine, when you lower your car, you are simply lowering the chassis closer to the ground and the suspension/axle stays at the same height. So… from what we have learned about four link design we can see what happens… the angle of the rods changes when the chassis comes down. Once you change the angle, you start to rob yourself of traction.
If you have a bad imagination; then here is something to help you visualize exactly what happens when lowering the car. The links become horizontal and look what happens to our tire load...
Now, if you still cant figure out why changing the angle of the links is bad… then you need to start over! But… to save you some time, it can be explained with pictures. Remember how the link help aids in traction? Well, after lowering the car.. look at what we have:
As you can see with the links out of that positive angle the thrust is simply driven forward and has no effect on tire load. Now on top of all this bad news, worn and soft bushings allow the grippy tire to simply bounce up and down instead of staying stuck to the ground and we get dreaded wheel hop.
So with these brackets, after you lower the car, they drop the mounting point on the axle down lower then before and thus creating a positive angle. Once again, creating tire load via axle thrust.
Regardless of what links or types you decide to use in your car, you should now have a better understanding of how they work.