Sandbags
Only real way would be to add a 50 pound bag to each side in the back although I do not think I would recommend this strategy. Better suspension components and tires will help you plant and launch better with less weight added. Although the sand would be quicker to install and cheaper.
I would do at the most, two 50pounds each side...But I wouldnt do it if you stock weight...If you were lightend alot and you really need traction it would be a ok idea..
But sus peices is a better thing to do..
Get some used Lower control arms






