Experimentally it has been shown that road cars have a friction circle, i.e. a car can pull a fixed maximum acceleration in any direction, determined by the tyres/road surface.
e.g. lets assume a tyre can give 0.9g force under braking.
This means that the car should be able to pull very nearly 0.9g cornering force. In low gears it may be able to pull 0.9g acceleration (if the engine/gearbox can sustain that).
It also implies if you do the maths that it can do about 0.64g braking AS WELL as cornering at 0.64g! The relationship is actually a Pythagorean law (C*C+A*A) = (0.9*0.9) where C is the cornering acceleration and A is the forward/backward acceleration.
However, doing maximal accelerations is risky; if you are braking and cornering and the car hits a small bump and enters a skid then your car may not be recoverable and you may crash. Additionally grip is dependent not only on tyres, but also on the road surface, and road surfaces are not entirely predictable.
Still, using combinations of braking and cornering can allow almost any car to go more quickly. Research has shown that racing drivers keep their cars close to the edge of the friction circle for their cars. However, some of the fastest drivers can actually keep their cars further from the edge; whilst lapping more quickly! Clearly, putting your car at the right
part of the friction circle is crucial!
Still, never forget the golden rule: Drive safely; it is better to go into a corner slowly and come out fast, that go into a corner fast, and come out dead.