12" possible

Your first question to yourself should be, why in gods name would you want to do something like that? Aside from looking completely retarded, unless you have the horsepower to make use of them (which you don't) you'll seriously hurt your performance.

EDIT
Nevermind....I thought you were talking about width, but I now realize you're talking about height...so disregard the above statement. In which case you need to ask yourself, why in gods name would you want to do something like that?