it increases the size of your front sprocket. ill try to put this so it is very understandable. have you ever looked at a bicycle and noticed if you change the gear in the front to a higher gear it goes to a bigger sprocket. then the pedaling gets harder and allows you to go faster. it is the exact opposite for the rear sprocket. the smaller it is the faster it will be able to go. up 1 tooth on the front is equal to down 2 in the rear.