I use 25 weight oil,and triple rate springs from rcraven.
It bottoms out only on the big ones 10 feet+ or so.
If your usin the stock tires,and your getting to much roll over...put a piece of tape on the inside of the rim to cover up one of the air release holes.The air will still release,but not near as quickly,and will make the tire feel kinda like its inflated....making it much more rigid.
CS