You may have to remove the center indentations on your fender bracket that is adjacent to your forks, that alone will give you the extra side clearance to go wider. I have run 130/90-17s and 140/80-17s by doing only that. With a 18" fat tires, you will probably have to add some extension plates as well, to clear the increase in diameter you will inevitably get. The extension plates are easy to fabricate and in the vault section of the forum and was posted by Keith awhile back. If you aren't clear as to what I mean about the cut out for extra side clearance, I can take a picture in the morning and post it for you as I currently have my forks apart on one bike. Although running with no front fender negates all this work to go through and does look pretty cool, especially with an oversize front tire, the amount of extra gunk the front tire throws at you and the front half of the bike makes just too much sense to not remove the fender, to my way of thinking anyway.
