Many enthusiasts tend to start vehicle preparation by focusing on the engine, as experience shows that a more powerful engine allows for faster speed gains, both in acceleration and in recovery. However, for those seeking track performance, the initial approach must be different: it is crucial to assess whether the limit lies with the vehicle or with the driver's skill.
When a popular car reaches 170 km/h or an electric vehicle provides 200 hp, it is likely that the limiting factor is the driver. Only after confirming that the car has reached its potential should refinements be considered, such as installing sports tires, heat-resistant pads, and more tolerant brake fluids.
After these initial adjustments, weight and mass distribution control follows. Subsequently, the suspension is modified, and finally, the engine. Generally, the focus on the engine is to maximize power, followed by selecting an appropriate gear ratio for the new torques and powers, while the differential is rarely considered, except in very radical track projects or drag cars.
Why is the differential generally not prioritized?
This is partly due to the lack of an extensive catalog of differentials for popular Brazilian vehicles and partly because the easiest upgrades to measure are preferred. A power increase compensates for imperfect cornering when the driving level is not extremely high. Heat-resistant brakes allow for more laps before the car cools down, but the differential does not directly contribute to grip nor generate torque; its impact is only noticed in fractions of a second and only when the car is fully prepared.
For this reason, many prepared cars keep the original open differential even after changing almost all other components. The real challenge arises when variations in grip between the wheels restrict the ability to transfer power to the ground, something modern electronic systems often mask.
If the goal is to optimize available grip without relying on power reduction or brakes, this is where limited-slip differentials, known as LSDs, come into play.
What does an open differential do?
The most common explanation for the limitation of an open differential is that it directs force to the slipping wheel. Although this reflects the driver's perception, the internal functioning is more complex. In a standard open differential, the gears allow the wheels to rotate at different speeds, but they do not freely distribute torque between them; the torque sent to both wheels is practically identical.
This implies that the wheel with less grip determines how much force will be sent to the wheel with more grip. Take the example of a front-wheel-drive car taking a corner: the outer wheel bears more load and can generate more longitudinal force before reaching its grip limit, while the inner one, lighter, transmits less torque to the ground. If the inner wheel starts to slip at 100 Nm, the open differential cannot force 250 or 300 Nm to the outer wheel, even if it has the capacity to do so. Thus, the usable torque on the axle is limited by the side with the lowest traction capacity.
This restriction makes the driver feel that all the force