Part 3: Suspension Components
So how are all of the above changes to the vehicle dynamics accomplished? Luckily for us suspension designers have created suspension components that will allow us to control pitch, roll, and their rate of change.
Springs - Allow us to control both pitch and roll.
Swaybars - Allow us to control roll.
Dampers - Allow us to control the rate of change in pitch and roll.
With these suspension components and how they are able to influence the vehicle dynamics, this leads me to develop the following sequence for proper suspension setup:
Step 1: Since your springs are the only suspension component that will control pitch, (while also affecting roll) you must first set your spring rates based on your pitch control.
Note: This is the source of much compromise for a street setup. You may find that the spring stiffness that yields the best results for handling are not the most ideally suited for comfort and daily driving. Comfort may very well become the driving factor in your selection of springs.
Step 2: Now that you have selected springs and those springs have not only changed the pitch but have also changed the amount of roll in the vehicle, we must set the swaybars to produce the desired roll stiffness.
Step 3: With springs and swaybars in place and dampers which are properly matched to the springs, we will now adjust the dampers to create the proper rate of change of both pitch and roll.
Damper tuning articles:
Koni Road Racing Setup Guide
http://www.amfmotorsports.com/prod/koni.1.1.htm
Neil Roberts Article on Shock Tuning
http://www.ozebiz.com.au/racetech/theory/shocktune1.html
Part 4: Real World Tuning Procedure
At least in my mind with the basis of this procedure routed in the procedure as outlined above, the process for proper suspension tuning as based on the performance of the vehicle through a corner becomes as described below:
Step 1: Alignment
Start with a basic alignment. At least -2.0 front camber and about -1.5 rear camber with zero toe.
Step 2: Testing and Data Acquisition
This step is where you must break a corner into three separate parts and focus on what the car is doing or not doing during each of these three parts.
1. Corner entry:
Corner entry is completely front suspension related. How the car behaves at corner entry will tell you all of the following things about your front suspension:
a) Pitch. How hard have you stood the car on it's nose during braking into this corner? Do you need stiffer springs - too much dive and unloading the rear end of the car? Do you need softer springs - too little weight transfer to load the front tires sufficiently to maximize braking?
b) Dampers. How was the rate of transition in the corner? Did the car react too quickly or too slowly? Did you shock the tire with to quick of a weight transfer, or do you not transfer weight quickly enough to allow the tire to find grip?
c) Roll. How much weight transfer did you get going into the corner? Was it too much or too little? Too much and you've taken the tire over it's contact patch and lost grip through camber loss. Too little and you've never transferred the weight the tire needs to stick.
2. Mid-corner:
This tells you about the steady-state balance of the car. Does the car have too much understeer or too much oversteer? This is the location of the corner where it becomes critical that the front and rear grip is very well matched.
3. Corner exit:
Just like corner entry is to the front end, corner exit is to the rear end.
a) Pitch: Are the springs too soft - the car squats under acceleration and weight transfers from the front causing corner exit understeer? Are the springs too stiff - corner exit oversteer?
b) Dampers: These are used to dial in oversteer on corner exit. Tight transition heavy course - dial the dampers back. Open sweeper corners - dial them up.
c) Roll: Once you have your rear springs set, use your rear swaybar to dial mid-corner oversteer.
Step 3: Tuning
From the information gathered by understanding what a car is going throughout the corner, the proper procedure to car setup involves adjusting these components in this order:
Start at corner entry.
1. Front springs - Set amount of corner entry brake dive.
2. Front dampers - Adjust to course layout and surface to control rate of weight transfer.
Move to corner exit.
3. Rear springs - Set amount of squat under acceleration.
4. Rear dampers - Adjust to course layout and surface to control rate of weight transfer.
Dial balance mid-corner.
5. Front swaybar - Set amount of roll stiffness in mid-corner (understeer).
6. Rear swaybar - Set amount of roll stiffness in mid-corner (oversteer).
Step 4: Alignment and Tire Pressure
With your suspension setup largely finished, you can now adjust your final alignment and tire pressure to tweak this setup to its full potential. These adjustments in alignment and tire pressures can be fairly effective adjusted based on tire temperatures. This is a very good article on this: Reading Tire Temperature
http://www.automotivearticles.com/123/Tire_Temps.shtml
Tire pressure:
Increasing tire pressures will yield an increase in grip upto the point where the tire's carcass can no longer hold the shape of the tire tread area and the tread will balloon out decreasing the tire's contact patch.
Decreasing tire pressure will yield and increase in the slip angle produced by the tire. Good for rear tires, bad for front tires.
Front tires - Increase the pressure in the front tires to yield the maximum amount of front grip.
Rear tires - To create oversteer, you can either increase the tire pressures to reduce the contact patch, or you can reduce the tire pressure to increase the slip angle produced by the tire. I would recommend lowering the pressure. This method of inducing oversteer is much more consistent.
This is a great section from Dennis Grant on Tire Pressures: Autocross to Win: Tire Pressures
http://farnorthracing.com/autocross_secrets12.html
Alignment:
1. Adjust your static camber to produce the largest possible contact patch.
2. Add toe out to the front to promote turn in and to the rear to promote rotation.
Part 5: Conclusion
I would like to leave you with these thoughts in regard to suspension setup:
1. Maximize front grip first and then dial the rear suspension to match.
2. You can steer the car with the rear tires. Loose is fast.
3. Everything with suspension tuning must be done in balance. It is the ability of the suspension tuner through the understanding and experience of all the different variables that allows them to find this balance. This is the art of suspension tuning, mixing all the correct parts to make the end result the best it can be.
Thank you very much for reading this setup guide. It is by no means complete and is very much a work in progress. Please feel free to discuss items, make suggestions for improvements, correct any errors, or clarify any over simplifications I have made. I'm still very much growing my understanding of car setup, and will continue to learn over many years to come.
Interesting reading:
Dennis Grant - Autocross to Win
http://farnorthracing.com/autocross_secrets.html