You should be in a gear which is appropriate to your speed. When I approach a corner, and I'm in no real hurry, I let the car slow down of its own accord until its well within the rev range for the next lower gear, then change down to that gear and begin to apply the brakes at about the same time. If I'm in a hurry (i.e. racing), I shift down the gears under braking. Thus the gears give me some braking to aid the brakes, with the added benefit that I'm usually in the correct gear for accelerating out of the corner. I THINK the theoricians agree with my approach, but I'm too tired to LIU. Help yourselves and tear me to shreds.