Unless formula one car suspensions have an incredible stiffness, these are one of the most important things to make a car drivable. It is probably one of the most difficult things that can be set on a car, and influences understeer and oversteer hugely. As tires are the only contact between the car and the road surface, you can image how important it is to keep the tires as good as possible on the track, no matter what bump or speed the car may encounter.
Forces to cope with
Weight transfer is the general term for most forces a car undergoes in any change of condition. It is a shifting of loading on the four outmost corners of the car. Acceleration means load is transferred to the back of the car, the opposite occurs when braking. In corners, most weight becomes lying in the two outside wheels. These kinds of weight transfer can be expressed and calculated with the following formula:
|dW = (m * h * a) / t|
- with dW symbolising the total weight transfer due to an acceleration a (m/s²),
- a total vehicle mass m (in kg),
- h the height is the height of center of gravity,
- t is the track width. (For longitudinal weight transfer, use wheel base instead of t).
Different types of weight transfer:
- Heave is the motion of the chassis when all four wheels go up or down in unison i.e. when a car drives through Aux Rouges at Spa, that car is pushed down onto the track, due to the surface which is basically a narrow valley. When thus driving over a hill, the opposite occurs and the car wants to fly away.
- Pitch is when the front and rear of the chassis go in opposite directions, either up or down. This occurs at braking when the car seemingly bends forward, or accelerating so that the car want to raise its nose.
- Roll is a side-to-side movement of the car. The suspension on the outer side of the car compresses while the inner suspension extends. This occurs during cornering.
- Warp is the movement of the diagonally opposed wheels in opposite directions i.e. the front left suspension compresses as the right rear extends.
- Yaw is the rotation of the car in a horizontal plane around a vertical axis. This occurs during cornering.
Weight transfer has to be absorbed or taken up by the suspension system, otherwise it will be expended at the tire contact patch meaning a loss of adhesion and a spin-out. How this weight is divided between the front end suspension and the rear end suspension is a relationship known as 'roll couple distribution'.
The above picture shows the virtual front of a formula one car without its nose. I must say virtually, as in reality, the rockers (see further) cannot be seen when taking off the nose, as they are placed a little deeper into the chassis.
Pushrod and pull rods are the diagonal bars between the car's body and the upright (where the suspension arms are attached to the wheels, near the brakes). There is always one for each wheel, but a car does not have pull and push rods at the same time. That would be completely useless, as these arms just do the same, it's only another way to get the same effect. The difference can be found in its name, as the pull rod pulls the rocker, while the push rod pushed it. On the picture we have push rods (when the wheel is pushed up, due to a bump or a turn-in, the push rod pushes the rocker up) connecting a rocker in the upper part of the chassis with the lower upright. A pull rod goes the other way, connecting a rocker located low in the chassis, with the upper side of the wheel, almost where the upper suspension arms meet the upright.
Pull rods were first brought to Formula 1 by Gordon Murray with Brabham in the 70s but gradually disappeared at the rear and then also at the front when teams started using high noses. It was Adrian Newey who put the pull rods back on the Formula One radar when introducing them in 2009 on the Red Bull RB5, a car that had brilliantly tight rear packaging compared to its competitors. Unless regulation changes are introduced however, pull rod front suspension is unlikely to return any time soon.
Rockers are also known as bell cranks or linkages. This is the lever that translates
the push\pull rods motion into the rotary force on the torsion bar and the up/down motion of the damper. the rocker also has mounts for anti roll bars (often referred to as ARB) and sensors for wheel travel. The rocker translates the wheel movement onto the dampers with a multiplicator. The movements of the damper are thus larger than those of the wheel itself. That means if a wheel moves 1cm, the damper will undergo a movement of about 2 to 3 cm (these are only estimated numbers). It's partially this principly of multiplicating the movement onto the damper that causes the enormous stiffness of the suspension.
On this particular drawing you can also notice the torsion bar passing trough the middle of the rockers. The torsion bar is thereby fixed onto the chassis, allowing the rocker to rotate around it. When a wheel pushed the rocker up, it twists and pushed the damper down.
As you can also see on the picture, both rockers on each side are connected with each other with an anti-roll bar (roll : see types of weight transfer). Anti-roll bars resist roll by twisting themselves, acting as torsion springs. The anti-roll bar should be handling approximately 50% of the front roll resistance, with the other 50% split between the front springs. To avoid some misunderstandings, a roll bar has nothing whatsoever to do with spring rate. Changing bars can only make the front end stiffer or softer in terms of roll rate and not spring rate.
The springs or torsion bars are the parts of the suspension that actually absorb the bumps. In simple terms, the softer the suspension on the car, the quicker it will travel through a corner. This has the adverse effect of making the car less sensitive to the drivers input, causing sloppy handling. A harder sprung car will have less mechanical grip through the corner, but the handling will be more sensitive and more direct, ideal for circuits such as Monaco where the drivers must be inch perfect between the barriers.
Shock absorbers on the other hand dampen the motion of suspension. They do not absorb impacts, but damp the motion of the vehicle. As the name itself says, it particularly acts on the first impact, while the springs work during the entire event. If you would have a car with springs, but no or bad shock absorbers, you will keep bumping up and down for a while, and in corners, a wheel might get off the ground a lot easier, because the opposite wheel bends down too much. Shock absorbers are thus tie-down devices for springs which control the springs' oscillation. Oscillation is the up and down movement of a spring, and unless it has a damping device on it, the spring will oscillate infinitely until internal friction in the spring stops its movement. Shock absorbers can be adjusted for rebound and bump.
F1 springs are made by specialist companies like Eibach and Koni, with springs often designed in part by the F1 teams to suit certain characteristics.
Packers or bump rubbers can be used to prevent the springs or torsion bars compressing too far. This allows the suspension to be soft, and prevents the car from hitting the ground due to high downforce or sudden track level changes. These packers should although not come into play in corners, because if the suspension is that soft that it leans on the packers in a corner, no more energy is dissipated into the suspension, which results in decreased grip. They are useful on modern cars to preserve the wooden plank under the car, the rules stating that no more than 1 mm can be worn during the race. (Hence Schumacher's exclusion from the Spa GP of 1994)