can someone enlighten me as to what exactly does a final drive do and why is it better to have, for example, 4.78 instead of 4.40.
thanks in advance

 

The final drive gear is just another gear your torque passes through before if reaches the ground. A higher final drive ratio means that more torque will reach the wheels in any given gear at the expense of top speed.

It's just like your regular gears. for instance in my integra 1st gear is 3.166 and second is 1.857. Now you know a car accelerates way faster in first than in second but you can obviously go faster in second.

A taller final drive allows you to accelerate slightly quicker, but you have to shift slightly sooner.

-Chris