The Super Close gear option is the same as having a Fully Customisable gearing setup, and setting it to be quite a small number for the Auto setting. Its purpose is to provide acceleration-biased performance - that is, each gear is shorter and closer to the others, and you will get through the gears quicker. This results in faster in-gear acceleration, as you're in the powerband more frequently, and you can also keep in the powerband more easily in corners. The disadvantage is that the rev limiter in top gear will come at you a lot quicker, and you will lose top speed.
However, it's only there as a cheaper option - if you can afford a Fully Customisable gearbox, Super Close is pointless, because the FC gearbox gives you the same possibilities as the SC one, but with so much more freedom.
What the info bar says about drifting and rallying is describing good uses for this gearbox - rallying, where top speed is rarely a factor and acceleration is everything, and drifting, where you have to be in the right gear in every corner to get it right.
Hope this helps.
DE
When they originally created GT, they seemed to have this idea for sort of an automotive adventure game.
You'd earn credits and need to spend them wisely in order to get the best value for money out of your car. The three types of transmission modifications, in general available for all cars, and with no unusual extras, have been basically unchanged since GT1.
So...
The designers wanted to emulate a cheap improvement, a reasonably-priced effective improvement, and a no-holds barred ultimate racing improvement. Actually, I'm sorry, but I can't remember off-hand whether there are three, or only two, levels of transmission improvement; I'm having a difficult time thinking of what the first level would achieve if the second-level was super-close.
But they never quite achieved their probable goal of forcing the player to spend money wisely.
One problem is that, even back in GT1 the price differences were rarely sufficient to motivate you to get anything but the best option. (Though sometimes when trying to do games in minimal numbers of game-days and races, saving the few Cr1000 could actually help your strategy). If you've got yourself lots of cash, you mights as well get fully-customizable (a somewhat unrealistic option actually; the gears available should be constrained in some way by allowable tooth-choices).
However, it might be worth checking the super-close option occasionally. Back in GT1, you'd actually sometimes get one more gear in that option than in fully-customizable. So, if the ratios were actually useable, it would sometimes actually be an advantage. And it would be an interesting quasi-Easter-egg if nothing else.
Just for reference, there are three gear ratio upgrades, and the first one is Close as opposed to Super Close - this one is meant to be like Super Close, but giving a bit more allowance towards top speed. Call the Close setup dropping the Auto setting, say, three clicks, and the Super Close lowering it six clicks.
That's why they're the same price, they do the same thing, just with varying levels of 'shortness'. If you've bought both of them, though, you should have got the FC setup
DE
Do you suggest use SC or FC ratio on 0-400 km(1/4 mile) ?
Is the Nitros have any effect on SC ratio (more accelrate)?