Thread: Suspension FAQ
View Single Post
Old 07-30-2006, 09:19 PM   #3
Wiisass
Zilvia Junkie
 
Wiisass's Avatar
 
Join Date: Aug 2002
Location: Philly
Posts: 486
Trader Rating: (0)
Wiisass has a reputation beyond reputeWiisass has a reputation beyond reputeWiisass has a reputation beyond reputeWiisass has a reputation beyond reputeWiisass has a reputation beyond reputeWiisass has a reputation beyond reputeWiisass has a reputation beyond reputeWiisass has a reputation beyond reputeWiisass has a reputation beyond reputeWiisass has a reputation beyond reputeWiisass has a reputation beyond repute
Send a message via AIM to Wiisass
Just a couple things I noticed that were wrong.

Solid sway bars are stiffer than a hollow sway bar of the same diameter. But they are also heavier and if you compare weight to stiffness you are actually better off with a hollow sway bar. The rate of a hollow sway bar depends on the internal diameter of the sway bar.

Solid endlinks will not artificially raise the effectiveness of the bar. Solid endlinks will allow the bar to perform as it was designed. As the bushings get softer more of the load from the arb will be absorbed by the bushing rather than transferred into the bar.

Also with sway bars, a stiffer sway bar will increase lateral load transfer which can be detrimental to handling.

About the shocks, compression damping mainly controls the unsprung mass, while rebound damping controls the body movement of the suspension. With stiffer shocks the car will takes its set quicker. Of course there is a limit for this, if the damper system is overdamped then it will actually take longer for the car to set itself. If the dampers are softer the car will oscillate before taking a set. Say you go into a left turn, the right side of the car will compress past the point that it would be in a steady state turn at the same lateral acceleration.

That might be getting too deep, but since most people have dampers that only adjust rebound or actually adjust rebound and compression at the same time, it's not as important to decouple these effects. So if you're adjusting rebound only, you want to look at the body motion if the car is taking too long to take its set, you want to increase rebound damping. You should increase rebound damping until you are happy with it, but keep in mind that too much rebound damping can lead to an initial loss of traction because of picking up the inside wheel and can also lead to jacking down over a series of bumps. If you're adjusting compression and rebound at the same time, you need to try and find a compromise between controlling the body motion and the motion of the unsprung mass. Compression damping will deal a lot with the ride of the car. Not so much in the low speed region of the shock, but more so in the high speed. When going over a bumper your in the high speed region of the shock, so if the shock is too stiff, these forces will be high and make the ride very harsh.

With all of those correlations, they depend a lot on the situation. I mean depending on what you're using the car for, you'll want different setups. There's a balance for everything and it all depends on if it's a street car or track car. That's a decent guide for adjusting the car when it's setup and everything is dialed in.

About adjusting caster. It's positive caster in the front. Increasing caster will require more force to turn the wheel, it will also increase the amount of camber gain with steer angle. Increasing caster too much can cause the wheel to get stuck at full lock. Decreasing caster will decrease the amount of force needed to turn the wheel and the amount of feedback at the steering wheel. The amount of caster you want depends on desired steer camber characteristics and the amount of mechanical trail. Mechanical trail is the distance from the wheel center to the point where the line connecting the upper and lower ball joint intersect the ground. A tire also generates pneumatic trail based on slip angle. This trail falls off as the slip angle increases. In order to help the driver feel the limit of the tire, the balance between the mechanical trail and the pneumatic trail needs to be determined. More mechanical trail comes with more caster, so by increasing the caster too much the driver will not feel when the front tires are at their limit.

Adjustable lower control arms will help to correct the roll center, camber gain in jounce and roll. With those arms you can also adjust static camber and track width.

The rear traction rod and the rear upper control arm essentially form one arm when considering suspension geometry. Setting up the rear of the car is something that should be done by someone who knows what they're doing. Bumpsteer will need to be measured. It gets difficult becuase of the way the arms are setup.

Bumpsteer should also be accounted for in the front. This can be done using bumpsteer spacers on the tie rod. Usually if you make the tie rod parallel to the lca, your bumpsteer will be better, but it's best if you actually measure it and space everything properly.

The picture your using for the subframe spacers are actually the solid subframe bushings. They will not adjust the angle of the subframe. Adjusting the angle of the subframe will tilt the inboard points of the suspension members will adjust the geometry of the suspension.

Alright, that's about it for now.
__________________
TIP Engineering
R/T Tuning
Drift and RWD Sport
DriftAssNation
Wiisass is offline   Reply With Quote