For shock's you would use:
http://www2.towerhobbies.com/cgi-bin...&I=LX3305&P=ML
there is different weights but it depends on your set up if you are not sure
ask someone where you race or let someone know what you are wanting to do
(Jump, run on dirt, flat ground etc.) and i am sure they can help you out here on hobby talk,
Hope this helps