Actually, manufacturers put a fair amount of engineering nous into determining tyre specifications. The manufacturers recommended pressures are designed to make the tyre contact patch as large and evenly weighted as possible, whilst also providing steering/handling, wear, and fuel economy characteristics that will please the greatest number of customers. Over inflating the tyres will feel like the handling and grip is sharper because at low cornering forces there is less steering weight. However, ultimate grip, which depends on maximising the contact patch in strong braking or lateral G situations will be reduced. i.e. ultimate braking and cornering grip will suffer, even if it doesn't feel that way. As an extreme example, look at how sensitive F1 cars are to tyre pressure (where a variation of just 0.2 kg/cm2 can “ruin” the performance of the car) to understand the effect on grip.