I need to buy a new chain and sprocket set and am looking for some advice. I have an 06 400ex and am a average trail rider, sometimes I lug all day long, but also like to keep up with my buds on the straights. There seems to be so many options with gear teeth I am not sure where to go. Any suggestions would help. Thanks, Rob

 

my ride buddy runs 14 front 39 rear and his 400ex is quick and hes quite the mud bug too it might actually be stock

 

I consider the 400's realitively fast. With that being said, maybe you need other than gearing.
Let's clarify..
Are they taking off much faster when you hit the straights? or: Take off out of the trail is fine but your in 5th pinned and they are leaving you?