The world champions are coming off Max Verstappen’s second place in the Singapore Grand Prix and Sergio Perez’s excellent performance in Baku, where he fought for the win for a long time. However, it would be premature to talk about a Red Bull recovery, given that the last two street circuits favored the car’s characteristics. The RB20’s issues lie in finding the right balance, a task that becomes more complex as the track’s layout becomes more varied.
Mechanical balance
In simplified terms, balance refers to the distribution of lateral forces exerted by the tires, indicating which of the two axles reaches saturation first. If the front tires reach their limit first, it results in understeer, where the car turns less than the ideal rotation for a corner, requiring the driver to apply more steering angle. The opposite phenomenon is oversteer, where the rear slides, and the front points towards the inside of the turn.
Balance depends on many factors, most notably the distribution of vertical forces between the four wheels. This includes aerodynamic load, which increases with speed. For this reason, mechanical balance, heavily influenced by weight distribution, prevails at lower speeds. The further the weight is shifted forward, the more the front tires are stressed, leading to understeer. Conversely, moving the weight back triggers oversteer. Ballast, which teams can move around the car, is a useful tool for adjusting mechanical balance by managing weight distribution between the front and rear.
Rigidity matters
Besides longitudinal weight distribution, lateral distribution also plays a role. When the car moves in a straight line, the weight on the right side equals that on the left. However, in a corner, the weight shifts more towards the outside, a phenomenon called ‘lateral load transfer.’ This dynamic reduces the available grip on both axles, which is detrimental to tire performance. It is possible to control its effect on balance by adjusting the mechanical settings of the suspension.
One particularly important parameter is roll stiffness, which is the suspension’s resistance to the chassis tilting outward. If we reduce the roll stiffness of the front suspension, we also reduce the percentage of weight that transfers from the inside wheel to the outside one, increasing front axle grip and reducing understeer. Conversely, softening the rear suspension moves the balance away from oversteer towards understeer. In conclusion, adjusting ballast and roll stiffness can correct mechanical balance at low speeds.
High-speed corners
Among the vertical forces on the tires are aerodynamic ones, which increase with speed until they become two or three times greater than the car’s weight. High downforce on the front ensures a strong grip for the front tires but reduces rear grip, causing oversteer. On the other hand, too much rear downforce risks weakening the front, leading to understeer. Adjusting the angle of the wing flaps is a useful tool for correcting aerodynamic balance, but it’s not the only one. You can also change ride height or the rake angle of the floor, altering the distribution of aerodynamic load.
At high speeds, the tools mentioned for mechanical balance—ballast and suspension stiffness—remain valid, but their effects impact all speeds. Altering mechanical balance to compensate for aerodynamic balance in faster corners is possible but risks causing imbalances at low speeds, where aerodynamic forces diminish. This isn’t an issue on tracks with corners of similar speeds, but unfortunately, such tracks are rare.
Ongoing evolution
Beyond the distinction between high and low speeds, it’s important to remember that a corner consists of multiple phases. The first is entry, where the car shifts weight forward under braking, affecting mechanical balance. In the exit phase, the opposite happens, with weight shifting to the rear, where more stability and grip are needed to transfer all the engine’s power to the ground. In between is the mid-corner phase, where the car travels at roughly constant speed with a stable steering angle, and its duration depends on the length of the corner.
During the phases of entry, mid-corner, and exit, the car undergoes movements, with the floor oscillating between different heights and angles, influencing aerodynamic balance. Under acceleration and braking, speed and the relevance of aerodynamics to mechanical balance also change, which itself is not constant. It varies based on load transfers and suspension movements, which affect roll stiffness, tire deformations, and angles relative to the ground. All these factors determine the available grip on both axles, and balance can shift even within the same corner.
The challenge of Austin
It is now clear why the Texan track presents a challenging test for a team like Red Bull, which struggles with balance issues. The 5.513-kilometre Circuit of The Americas in Austin features both high- and low-speed corners, a mix that becomes problematic when there is an imbalance between mechanical and aerodynamic balance. There are also short corners with sharp direction changes, where entry balance is key, while exit balance becomes crucial in the many hairpins. Additionally, there are longer corners, especially the triple 16-17-18 complex in the final sector, which are taken at high speed and where mid-corner balance is essential.
The Texan circuit is far more varied than Baku and Singapore, which are relatively homogeneous in terms of corner types, with mostly short, 90-degree turns within a similar speed range. Red Bull is confident that the new floor and setup tweaks have brought the RB20 back on track, but only the variety of Austin will determine whether the work done has been successful.
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