i have stock suspension and have never encountered this. this is a problem with toe angles. the front tires are toed tooooooo far in for this to happen. You have to check your alignment every now and then. Your car wont pull or drift if the toe is toooooo far in so you cant check by that. Hook it up to a rack every now and again and stuff like this wont happen. If you hit a really bad pot hole or a curb or drive on low aired tires then you might want to check your alignment and do some correcting. its not that hard its just something you have to keep a eye on. you should make it as important as changing oil because of the fact of a big waste of tires it can become

 

There is another factor to consider is SAI (technically referred to as Steering Axis Inclination ). SAI is the imaginary centerline through the center of the strut down through the center of the lower ball joint. This can go out of spec by either wear or by the strut getting bent by road hazards or by bottoming out too hard. When SAI goes out, so does the toe at the same time. When the SAI is out of spec, all the toe adjustments in the world won't fix your problem. Steering geometry needs to be brought back to spec to rid you of this problem.Along with a pair of new front tires because it's the only thing to do !

 

also if you ever test for alignment purposes, camber wont make the car pull or drift its "cross" camber that will make the car a little screwy and the SAI can effect that as well. SAI problem can be caused by almost any damage suspension product. like for example, if you bent up your k member a little bit or say your A-arms, then that can have a effect on it. theres a lot to keep in mind, and knowing all your angles and factors is a little hectic at first but then it pays off.

 

I guess the obvious question no one has asked is how hard do you drive your Mustang? if you drive it really hard then that type of wear is to be expected. My 4 outside edges are pretty rounded off as well but evenly. If you do not drive it hard then yes you most likely have a problem and need an alignment. I have a 2005 GT and a 2006 V6 both with the same 17" stock GT rims. both in stock configurations.

the GT I drive VERY VERY HARD. my front insides look like that after 20000 miles on the button. Can make it last a little longer if I take it easy, but rarely do. I replaced fronts 3 times. third set just today from AmericasTire as a matter of fact $247 and change out the door for 2 17" P Zero's not bad price. Rears lasted 38000 but worn all the way down till you could see air. If yours is a GT you can relate. I had an alignment from Villa Ford after second set as I had the same concern but still wore them down exactly the same as before.

the V6 gets driven like and by a "girl". barely has 25000 miles on it and the tires are wearing pretty even. Front and back could be the weight difference but I doubt it in my case anyways.