i jus got a 400ex and got a free pair of 250r front rims and tires.....the tires are alot smaller then the stock wheels......it is very shacky on the trails.....could it be becouse there so small ...and how can i see if the shocks are ajusted for a heavy rider?

 

Got an owner's manual??? It will tell you what the "stock" suspension settings are. I would reset it to stock, then ride it and adjust it to your personal taste after that:

http://atv.off-road.com/atv/ar...eDetail.jsp?id=192286


The shake could be tires or even a bent rim.

Not sure what you mean by "smaller" tires. In any case, I would ditch whatever it has on it, and get some aftermarket tires. I run ITP Holeshot XC's, but I ride desert. I also like to run ITP rims, because they are wider than stock and have a greater offset. This makes the quad several inches wider...for a real nice increase in stability.

 

they are dougles rims that are almost brand new and same with the tires but they make the quad sit like 2 inchs lower becouse the tire is so small ...they are off of a 250r....i have a picture of it but dont kno how to put it on here?

 

It sounds like a common tire to run for MX, the small front tire grabs better in the corners but may not be likeable on the trails.