Do you have to cut the original arch or will you roll the lip ?

??
Guess it didn't make much sense.
What I was getting at, I assumed the wider fenders are to accomodate wider wheels.
Normally on Yank cars you can roll the lip of the arch so it doesn't rub on the tyre, but if its not enough you have to cut away the offending metal..
Hmmm... confusing myself now