Briefly: the modification corrects the too harsh Voodoo physics, which San Andreas got from Vice City and makes it more similar in its behavior to other cars by removing the so-called. "arcade" agility and super-responsive control.
In detail: the history of car physics (specifically handling.cfg and all the game code associated with it in the EXE) developed in such a way that it was San Andreas that received a major addition to the physics already in the game. The game has been updated with several new parameters, the key of which is the so-called turnMass or the mass of the car when turning (rotation mass), which radically affects the feeling of using the cars. A few other parameters were also changed and corrected, but they were not so significant and here Rockstar made the choice to start changing the already existing settings of cars from previous games (III and Vice City) to make them feel different to the player. Many cars in the game retained the same settings from Vice City, while many were subject to this stylization trend due to the fact that in III and Vice City the settings of the cars were very sharp, at high speeds and (mainly in GTA 3) were almost always full drive: all this was a legacy of the arcade spirit of GTA 2. Therefore, we can already make a brief conclusion about what basic settings were subject to stylization in San Andreas and what needs to be changed in comparison with previous parts in order to get the same result - grip, acceleration speed , drive: these are the main characteristics that have undergone such changes in handling.cfg these are the parameters (J) (K) (L) - clutch; (O) (P) — acceleration and inertia of engine acceleration; (Q) (R) - type of engine (drive).
Typically, to get the desired result, Rockstar simply lowered these parameters (JKLOP) and tried to base the engine type based on real life, where possible and compatible with the game. Specifically, we just need to take the clutch setting, which has clearly been simplified (just like the maximum speed and acceleration of the engine, but we don’t need them, because this will affect the game balance), therefore we can simply take the settings (JKL) responsible for clutch and get a more reliable result. By the way, I will not deny the hypothesis that perhaps this very setting was prepared for San Andreas itself, but in the end it could only be used in Vice City Stories, since when developing City Stories games Rockstar Leeds clearly used the source code of San Andreas in order to improve player control based on Vice City and add new features to diversify the game (that is, the physics of City Stories may be an early version of the physics of San Andreas cars, since they have the same parameters with minimal changes, this hypothesis was discovered during reverse of Liberty City Stories which has some confirmation).