what is the biggest rear sprocket you've seen for the 400ex. Where did you see it( if you have one a webite would be nice) and how much. I want a 0 or 41 tooth

 

Why don't you just drop one or more teeth on the front sprocket? Doing this is like adding several teeth to the rear sprocket and you won't have to replace your chain. I have a 14 tooth front sprocket on order.

 

The biggest rear sprocket for the 400EX is 45teeth and you can find it at James Lucky ATV Products (page 29 in their catalog) 1 800 233 2637

 

Dont change the rear sprocket it is better to change the front sprocket to get gear ratio changes. I have a 13, 14 15, and 16 tooth front sprocket and only have to change the rear to a 39 tooth to have enough chain adjustment with the 13 tooth front.