Try to be in the right gear when you enter the corner. The whole idea is to keep the suspension loaded about equally front to rear, to maximize the available traction on both tires. When you roll off the throttle and pull in the clutch to shift, you end up shifting weight to the front tire and unloading the rear tire some. This can upset your traction. What you should be doing is a smooth, slow roll-on after the turn in. When you are leaned over, you are on the smaller diameter of the outside edge of the tires, which effectively changes your gearing and causes the bike to s down some. This isn't indicated by the speedometer, but it happens. When you slow down, you shift weight to the front, thus the slow roll on to keep a steady speed through the turn, thus keeping the supension loading constant and balanced and not upsetting the traction. Then, you simply continue the roll on as you straighten the bike up at the exit of corner. It is better to be a little slower going into the corner, choose the gear you need before you turn in and be smooth rolling on through the corner. Always look through the corner, also. Look where you want to go. You will go where you are looking whether you want to or not, so it might as well be where you want to go.