I did a search for you on this site using the keywords " 18 wheeler , semi, and rig " but I'm not getting any results. ( confused )
The reason why I did this, is that there are
several posts already devoted to this. We have discussed this several times.
Sorry I can't seem to be able to use the search function correctly, but if you search through the 'aerodynamics' part of the forum, you will eventually see several of these postings.
( One thread - mine actually - comes to mind entitled 'Accordian kammback for big rigs ?" It's long dead BTW.)
Good luck
http://ecomodder.com/forum/showthrea...-1-a-7201.html
http://ecomodder.com/forum/showthrea...rigs-6090.html
http://ecomodder.com/forum/showthrea...-van-3948.html
http://ecomodder.com/forum/showthrea...kers-1689.html