I have a 2000 400ex and I need to replace the chain and front/rear sprocket, and im not sure what sizes work best.
The motor is stock but its got an aftermarket pipe and jetted.
I do alot of trail riding, but I also go to the dunes, so i need the best sizes for all types of riding.

thanks!

 

I know stock gearing is either 14 or 15 in the front, and 38 in the rear.

 

Yeah, stock is 14/38. But if your riding varies a lot, get a 13, 14 & 15 for the front and change it depending on what you are going to do. I change the front on my 250X and it takes me 5 minutes. There's not enough difference to make me have to readjust the chain tension. And those front sprockets are cheap. $12 each or so.

 

Welcome to the forum, from the riding style you said you do I would go 1 tooth down in the front for trails and especially in the sand you sound like you need more power than speed.