Can someone tell me the kind of spacer that are good gor an xB with rims
size 18 x 8.5

 

The best answer would be "none." Because you were willing to do your homework and order a set of wheels with the proper offset.

An accurate answer to your specific question would be... "There is absolutely no way to answer your question without more information." We must know the wheel offset, the suspension you plan to use, the tire size you plan to use, and what "look" you are trying to achieve.

Hope that helps.