We all know more rubber on the pavement means more grip, but unless your car is an open-wheel racecar, the size of your wheel wells limits how much rubber you can stuff under your car’s fenders. So, it’s important to maximize fender space to fit the widest tires possible—without shredding them as you leave your driveway.
Many car fenders have a formed lip around the wheel opening that adds stiffness, or is just a byproduct of the manufacturing process.
But, if you’re looking to fit wider rubber and get that “flush” look, the fender lip is usually sharp—and metal—which will slice your tires faster than a chef at Benihana. Old-school methods of flattening the lip or “pulling” the fender away from the tires usually involved a baseball bat or a trip to the body shop (or both!).
The modern method of opening up a wheel well is to use a “fender roller,” with the most common one being available from the Eastwood Company. These handy tools attach to the wheel hub and use a polyurethane wheel to bend the fender lip while the user rotates the tool back and forth along the wheel opening. A series of adjustments can change the angle and force applied to the roller during each pass until the lip is formed to the desired shape.
Bending the fender lip can cause the paint to crack. As paint ages, it becomes brittle, and may not flex enough to avoid cracking while bending the lip. Using a heat gun to warm the paint to 120-140°F will soften the paint and help avoid too many cracks.
We decided to try this with a 2003 Mustang Cobra that we were preparing to receive some wider rear rubber. In addition to adding 295mm rear meats, our recent switch to a Maximum Motorsports front cross member and control arms pushed our 275mm-wide front tires out beyond the edges of the fenders. Because of our low ride height, the tires rubbed the fender lips when we drove over big bumps.
We borrowed a home-built fender roller from Coffey Fabrication and Race Prep in Nashville, Tennessee, dusted off our heat gun, and got busy. Similar tools are available from companies like Eastwood. We found that by applying pressure to the fender lip, the fender roller did two things:
1) Subtly deform the whole fender to “pull” the wheel arch out.
2) Flattens the fender lip itself.
Our Mustang has two different types of fenders: the front fender is made from thin, single-wall sheet metal. But it has a thick, U-shaped fender lip. While the fender lip is stiff, the rest of the fender is quite flexible.
The rear fender on our Mustang is an integral part of the unibody structure, with steel inner and outer fender panels that are pinch-welded along the wheel opening. This construction makes the whole fender very stiff, but the lip itself is only a flat seam about an inch wide.
We started with the front fenders. After we attached the fender roller to the hub, we adjusted the wheel so it contacted the fender lip at the desired angle. Then, we gently warmed up the paint with our heat gun to 130°F. With the paint up to temperature, we swung the roller back and forth along the fender lip.
After a couple passes, we adjusted the roller angle and applied a bit more pressure to the roller wheel. We alternated warming up the paint and making additional passes with the roller until we were satisfied with the results.
The rear fenders on 1979-2004 Mustangs feature a sharp, pinch-welded seam that’s a perfect tire slicer. With the suspension compressed, we marked the start, middle, and end of the most problematic area.
We were unable to drastically change the front fender lip’s shape with the roller. However, the pressure of the roller gently deformed the whole fender and “pulled” the fender lip out to add the clearance we needed. We finished the front by painting the areas were the tires rubbed through the paint.
At the rear, we began with the roller a few degrees different than the lip, and changed the angle of attack after every couple passes. How the fender lip behaved under the pressure of the roller was drastically different than the front. Rather than pulling the wheel arch out, we were able to flatten the fender lip itself.
We learned to not get “greedy” and bend too much at one time.
Making small adjustments to the roller and not forcing the fender to bend too much at one time yielded smoother results and less paint damage. We spent about 30 minutes on each fender.
Surprisingly, we only made a few hairline cracks in the paint—but perhaps we hadn’t warmed the paint up sufficiently in those spots. We’re not complaining considering our paint is twelve years old!