What Are Rocker Panels?Last Updated November 17, 2023 | Meghan Drummond
Running between the front and rear wheel wells, we step over our rocker panels every day, and yet, even some car enthusiasts would be hard-pressed to explain exactly what rocker panels are or why they exist.
Understanding why this part is important and knowing how to maintain it can help you avoid the cost of replacing rusty rocker panels.
What Are Rocker Panels?
Despite your rocker panels’ humble appearance and location, they serve an important function. Very few pieces exist that actually tie the front of a car to the rear, but the rocker panels do exactly that.
Rocker panels run along the length of the car where they add rigidity to your vehicle and create unity.
Unfortunately, because they are placed so close to the ground, rocker panels frequently get rusty and need to be replaced. The cost of fixing or replacing rocker panels depends on which type of rocker panel replacements you are thinking of getting and how serious the damage to your current rocker panels is.
What Rocker Panels Do
In the 1950s and 1960s, when cars were largely unibody constructions, rocker panels were needed not so much to connect the front to the rear, but rather to provide a little extra support to keep the middle of a car from sagging.
In modern cars, rocker panels connect the front of the car to the rear, giving the car additional rigidity that contributes to better handling. You really only see the rocker panel when the car door is open.
Rocker panels help to protect the cabin. In a modern car, crumple zones are crucial. The front of your car and the rear need to crumple in order to absorb the impact of an accident and allow you to walk away intact. The rocker panels help to make sure the cabin of the car doesn’t deform in a way that could harm the passengers.
Essentially, in an accident your car’s job is to turn into a smushed can protecting an interior capsule. The rocker panel forms the bottom edge of that capsule.
The rocker panels of trucks and off-road vehicles not only do all of the above, but they also function as steps for their drivers, helping them to climb the sometimes substantial heights that we ask people to overcome to use a newer truck or Jeep.
Truly, rocker panels are the unsung heroes of the automotive world.
Why They’re Called Rocker Panels
No one is really sure where the name rocker panel came from, but there are some good theories that all help to illustrate where the name may have come from, as well as the many purposes of rocker panels.
Some argue that it’s because the rocker panels on old vehicles from the ’60s were chrome and a part of “rocker” culture at the time.
Four-wheel drive vehicles sometimes use their rocker panels to actually “rock” when they’re stuck in a particularly precarious situation.
Stagecoaches also used to have rocker panels. These panels were largely aesthetic and were used to hide the fact that the floor of the stagecoach was deeper than the door. Rocker panels ran along the edge, hiding the strange proportions and creating a balanced appearance.
Some have wondered if it’s because the rocker panel is the part of the car that gets beat up by rocks while you’re driving (though, in my experience, that part is actually usually the windshield).
In other countries, what we refer to as the rocker panel is actually called a sill, as in windowsill. Like a windowsill, the rocker panel forms the solid foundation on which the rest of the car is laid.
People often get side skirts and rocker panels confused, but the function they serve is very different. Side skirts are aftermarket parts that attach to the rocker panels but aren’t part of the actual structure and don’t supplement or strengthen them in any way.
In track cars, side skirts help to improve the aerodynamic performance of a vehicle by splitting the air. They’re sometimes called side splitters for this reason. Tractor-trailers have their own version of a side skirt that’s designed to help reduce drag that you may see while riding down the highway.
In terms of style, side skirts can help your car appear longer and lower but don’t improve daily driving much.
Some people have argued that having a side skirt helps to protect your rocker panels but there really isn’t much evidence to support that. There are covers available for rocker panels that many in particularly snowy and icy areas are fond of, but ultimately good maintenance is the best protection available.
The rocker panels are one of the few spots that almost everyone misses when they’re cleaning their car. They’re low to the ground and easy to overlook. In order to really clean them, you need to bend down to the ground and scrub, something a lot of people aren’t willing to do for their vehicles.
The rocker panels ride closest to the road as you drive, where they’re continually coated in all of the road debris, the salt, the de-icers, and every other gross thing you drive through (don’t think about this one too hard). The result of these chemicals is that the metal of rocker panels quickly becomes corroded and as it does it becomes susceptible to rust or rot.
Rusty rocker panels are one of the first things people look for in a used older car. Mostly because they are nearly guaranteed to be rusty, and it’s a good way to get the dealer to knock a few bucks off. People just don’t do a good enough job of cleaning their rocker panels. If your rocker panels are only suffering from light rusting it's fairly easy to remove surface rust.
Unfortunately, patching rocker panels isn’t as easy as it was in the days of the unibody frame.
Back before rocker panels were so structurally integral to the daily driving of the car, people would repair their rocker panels with fiberglass repair kits when they started to show substantial signs of wear and tear. They could get away with that because their rocker panel wasn’t responsible for holding the whole car together.
Considering people literally use a truck’s rocker panels as a step, you’re going to need something more substantial to patch them with than a little bit of fiberglass.
Maintaining Your Rocker Panels
If you’re buying a new car, or if you happen to be driving a car with nearly perfect rocker panels, then consider this an incredible opportunity. Maintaining your rocker panels is much easier than having to replace them.
The most important thing to do is clean your rocker panels regularly. If this sounds easy, then you’ve never tried to do it. Dirt gets packed in and worse than dirt, you’re going to be contending with tar, and you’ll want to contend with it gently so that you don’t take your paint right off with it.
Patience is going to be necessary for any rocker panel cleaning. WD-40 has been recommended by many as a good cleaner that will remove tar without removing your paint. To try WD-40, spray, wait for it to soak, and then gently wipe to clean.
A lot of people notice that they have a clip-on rocker panel and get excited thinking that they can easily remove and then replace it. This is not the case. The clips are basically one-and-done units that you’ll need to replace if you choose to remove them. That said, removing and replacing them on a classic car can be a good way to make sure you’re keeping it protected from rust.
When it comes to cleaning your rocker panels, you’ll want to bring everything you’ve got. Pressure washers and foam blasters are tried and true methods. A good detailer would be able to do a great job with your rocker panels and many even pride themselves specifically on their rocker panel methods.
After it’s clean, coating your rocker panel in a protective layer of wax or ceramic is a good way to keep it from getting rusty, as are more traditional rust preventives.
An ounce of prevention is worth a pound of cure, and keeping up with this maintenance is a good way to make sure that even if it gets dirty it’s not going to get rusty. Rust grows, spreads, and eats through metal like locusts through grain. It does not fool around, so you can’t either.
Covers are another great way to protect your rocker panels and are especially worthwhile in off-road vehicles that are frequently coated in mud.
If you want to learn how to install rocker panels on a classic unibody using little more than a drill, a riveter, a friend, and a piece of string, check out our classic Mustang rocker panel install guide.