whats the biggest front sprocket i can put on a 400ex and the smallest i can put on the back

 

Other way around dude

Peace
Willfulone

 

a gearing calculator says it will go faster like that

 

That gearing calculator is great but it leaves out one minor detail. You have to be able to pull the gears you put on.[img]i/expressions/face-icon-small-wink.gif[/img]

 

They offer a 16t front and a 36 rear those are the extremes for top end. that is if your motor can even push that. A lot of guys go down in front for better accel. I personally went to a 16t front and kept the rear stock and it works awsome. I have some good mods however to push me through all gears. Still cant keep front end down and still can pop plenty of wheelies. I wouldnt suggest going 16t on the front on a stock 400. I do alot of straight riding on roads and long trails. Front sprocket is easyest to change however, so if you want to upgrade the sprockets are only 17 bucks about and its the easyest to change.