What Are Rolled Fenders?
Under nearly every fender arch, there is an inner lip where the outer body sheet metal joins up with the inner fender well metal. The two sheets are welded together and the seam is then sealed to prevent corrosion. This is typically more apparent on the rear fenders, and it creates a lip that protrudes inwards towards the tire. When using tires that are wider than stock, this lip can rub on the tire when the suspension compresses. This rubbing is more of an annoyance than a serious problem, and it can be easily remedied by rolling the inner lip flat.
This can free up an additional 5-10mm or more to fit wider tires without rubbing, and is very common for track builds and pretty much standard for race cars that are still using the stock body.
Diagram from Eastwood's fender roller tool manual
How do I do it?
While this can be a DIY, we don't recommend trying it yourself for the first time on a car where you wish to maintain a perfect appearance. We recommend having this done by a qualified body shop who has experience rolling fenders on your particular type of vehicle. The procedure involves heat and re-shaping metal, which must be done carefully to achieve proper results. If rushed, or done improperly, this can lead to paint flaking or a disruption to the body lines of the fender. If done properly, the inner lip rolling will be completely unnoticeable from the outside. This maintains the stock outer body lines of your car.
Types of Rolled Fenders
There are various degrees of fender rolling depending on how much additional space is needed:
Light fender roll - This method retains the outer shape of the body leaving the car looking completely original from the outside.
Medium fender roll - This flattens the inner lip against the body, and may bring the actual fender arch outwards just slightly to create additional clearance.
Heavy fender roll - This will visually alter the appearance of the fenders, and should only be done with a "there's no going back" mindset. You should be pretty committed to your goals for the car if you're going this route.