gixxerdrew
DSM Wiseman
- 664
- 21
- Oct 5, 2007
-
Yokohama, Japan,
Asia
Continuing the topic from the last DSM handling tips installment, we talked about some advantages of the split lower control arm setup and how to make the most of it. Next we used a combination of bearings and bushings to create a desirable dynamic effect on the suspension geometry.
First we lay down some simple facts, a drag race suspension setting is not a good road course suspension setting. Maximum traction and maximum lateral grip require totally different compromises. In our case we have a high HP FWD car and we need to maximize our ability to accelerate in any conceivable way.
There is an inherent amount of flex in any suspension, the control arms, the bearings or bushings, the pickup points, the chassis itself, everything flexes under load. Bushings are designed to deflect and absorb harshness.
Any item in 3d space (in this case a tire/wheel) has 6 degrees of freedom, as such you need a device to control all 6 or your suspension will leave your wheel flapping about. A lower control arm typically constrains two degrees of freedom, forward and aft on the car as well as left to right. Since we have a split lower control arm there is one specifically controlling each of those. The advantage to be gained here is that forward lower control arm moves on its own arc. There are way too many dynamic effects as a result to talk about all of them here, we will just talk about one specifically. Acceleration load and camber.
Figure 1: conceptualized control arm rotation (image is not accurate, just to show the concept)
As you can see in figure 1 the control arms will move the ball joints on an arc when placed under load in the direction indicated by the arrow. The amount that they move is dependent on the amount that the bushing flexes in the rear lower control arm since this is the arm that constrains the motion on that degree of freedom. The result of this as you can see from the image is that both lower ball joints move inboard on the car under acceleration. If the lower ball joints move inboard, but the upper ball joint stays put, the camber will change in the direction of positive camber.
This was used to our advantage by tuning the flex of the bushing and by using spherical bearings in all other pickup points we can control our camber dynamically under acceleration and deceleration vs cornering forces.
This allowed us to get the car to hook like a drag car in a straight and under braking but maintain a certain amount of camber in corner. Of course there were compromises involved testing was a necessity! We also had to optimize alignment settings to take into account what everything would be in corner vs on the alignment rack. This was one of the secrets to maximizing performance for us!
First we lay down some simple facts, a drag race suspension setting is not a good road course suspension setting. Maximum traction and maximum lateral grip require totally different compromises. In our case we have a high HP FWD car and we need to maximize our ability to accelerate in any conceivable way.
There is an inherent amount of flex in any suspension, the control arms, the bearings or bushings, the pickup points, the chassis itself, everything flexes under load. Bushings are designed to deflect and absorb harshness.
Any item in 3d space (in this case a tire/wheel) has 6 degrees of freedom, as such you need a device to control all 6 or your suspension will leave your wheel flapping about. A lower control arm typically constrains two degrees of freedom, forward and aft on the car as well as left to right. Since we have a split lower control arm there is one specifically controlling each of those. The advantage to be gained here is that forward lower control arm moves on its own arc. There are way too many dynamic effects as a result to talk about all of them here, we will just talk about one specifically. Acceleration load and camber.
Figure 1: conceptualized control arm rotation (image is not accurate, just to show the concept)
As you can see in figure 1 the control arms will move the ball joints on an arc when placed under load in the direction indicated by the arrow. The amount that they move is dependent on the amount that the bushing flexes in the rear lower control arm since this is the arm that constrains the motion on that degree of freedom. The result of this as you can see from the image is that both lower ball joints move inboard on the car under acceleration. If the lower ball joints move inboard, but the upper ball joint stays put, the camber will change in the direction of positive camber.
This was used to our advantage by tuning the flex of the bushing and by using spherical bearings in all other pickup points we can control our camber dynamically under acceleration and deceleration vs cornering forces.
This allowed us to get the car to hook like a drag car in a straight and under braking but maintain a certain amount of camber in corner. Of course there were compromises involved testing was a necessity! We also had to optimize alignment settings to take into account what everything would be in corner vs on the alignment rack. This was one of the secrets to maximizing performance for us!
