let me start this by saying i'm an incredibly anal person. i don't deal with paint cracks and damage very well.
anyway, i wanted to run eibach 15mm studded spacers on my 08 mazdaspeed3. at the time, nobody was running them and i figured it would be the ideal way to make the OE wheels flush. i was running the stock size tires (215/45/18) and my car was lowered about 1.5" in the front and 1" in the back.
went from this
to this
the front cleared no problem.
the front of the rear wells would catch under certain circumstances and would pull the lip up there, and then it would hit all the time until i tapped it back with a mallet.
so i decided to listen to all the people who said it would be fine with a heat gun and a professional roller.
my friend, who has rolled many a e30 and e36 bmw fender lip, brought his roller home from work (a bmw race shop). we heated the paint up really good...consistent, but not too hot, and slowly went to work. gradual stuff, really gradual, where we'd do slight angles and gradually increase them.
well, the paint on a modern cars is so damn incredibly thin. and i knew that. but didn't listen to my gut, and the paint cracked all over the place. i was so bitter because i knew i should have just gone another route instead of trying to make this super thin mazda paint stretch.
so, i ended up taking the car to get the fenders really rolled, by a body shop. not too much so the structural integrity of the fender was compromised, but a decent angle. that involved obviously a ton of body work, and the car was silver metallic and obviously two stage so the paint/clear had to be blended FAR.
the body shop i used was different from my normal shop, as my normal shop was booked solid. again, went to this new shop on a recommendation and it was a nightmare. i won't get into it but they ###### my car up and i had to do a chargeback and almost sue the guy. my normal shop fixed it but my car was off the road for a total of 3 months because of all of this.
the moral of this story is, if you care about paint cracking, don't do this on your late model car.
take it to a legit body shop and have them do it right. it will cost money but otherwise you run the risk of a crappy job.