how wide can i go??

right now i have 17x9 cobra r rims and i got 255s on them. i have a 1/4 inch spacer on there right now too. my tires do not grip the road at all. 1st, 2nd, 3rd, and 4th gear as soon as i hit boost the tires spin. im like dam what the hell. how wide of a tire can i put on a 17x9 rim. also ive heard something abotu turning around the shock or something to fit a wider tire???? whats the truth behind that??

i am also going to be getting upper and lower control arms so that should help also.

thanks
steve