I tried that before and it did not work well, but then that was a bodyguard I tried it on ;)

Anyway, you can kill most cavalry with 1 charge from the front too if you align them properly:

Your cavalry needs to charge through the tiny gaps between enemy cavalrists.
If that happens, they will basically mow them down. Works best if the enemy cav is moving towards or away from you. Once charged into such a cav unit the above way and out of 32 men, they had 2 left.
If your cav hit the enemy head on, ie. facing straight, regardless front or back, you will hardly do any damage and those of your cavs which end up walking along the sides of the enemy cav will be killed.