idler gear!? Help me please!

[Bassbrdr1987]

I see this gear on the tower hobbies website called an idler gear. Im relatively new to r/c cars, and i have no idea what that is. Will it help my performance? What the heck does it do!?

If someone could help me, id be very happy. Either post here or send an e-mail: bassbrdr1987@aol.com thanx.