I'M PLANNING TO CHANGE MY BACK SPROCKET SIZE ON MY 400EX UP TO A 39 TOOTH DO I NEED TO GET A NEW CHAIN AND IF SO WHAT SIZE

 

I DONT KNOW IF YOU CAN GET A 39 TOOTH, MY BUDDY
BOUGHT A 41 TOOTH AND IT WOULD NOT FIT HE NEEDED
TO BUY A BIGGER CHAIN

 

I don't remember what the stock size is for the back sprocket on the 400EX. I want more low end so I'm changing out the 15 tooth front sprocket and replacing it with a 14 tooth. This way I won't have to shorten or lenghten my chain, just readjust it. Its easier to change out the front sprocket compared to the rear sprocket anyway