Tech Corner: Mounting Side Steps? Consider This First

As 2019 is gearing up to be the Year of the Truck, you might be eyeing up some aftermarket running boards to really make that sweet new ride pop. There are plenty of styles and sizes available—from traditional long, flat running boards and more pronounced-looking nerf bars, to simple space-saving side steps or a variety of all three. We’re here to focus on the smallest of the three: specifically, mounting side steps.

With side steps, I’ve found that while the design may be simpler, the installation can be complicated—go figure. Not all side steps mount to the same location, and not all will be exposed to the same forces. Should you choose a rocker-panel mount or a frame mount? If the installation requires drilling, what are the consequences? And what kind of hardware is the safest bet?

Gut instinct points to something frame-mounted as the safest option because the frame is the strongest part of the vehicle, right? And logic tells me that Grade 8 bolts are the right choice no matter what, as they have a higher tensile strength compared to Grade 5, correct? Then again, Grade 5 bolts might handle shear forces better—which would be higher on a frame-mounted design. So, does the hardware change depending on the mounting location? And does the location really matter that much?

Let’s make heads or tails out of mounting side steps.

The Side Steps Make the Man

Before we get to the installation of side steps, first you have to pick a style or configuration that suits your truck and lifestyle. If you’re just looking for a simple foothold to get in and out of your truck, a space-saving hoop step might be your best bet. But if you’ve got balance issues, limited mobility, or any small children who need to climb in and out of the cab, a wider side step like a shortened running board, or even a drop-step nerf bar, like this one from Westin, might be a smarter choice.

Photos: CARR’s Hoop II Steps provide a durable non-slip surface with a rugged, yet polished look.

Before blindly buying a set of steps based on appearances alone, you also want to consider the life of the step. Think about the lifestyle of the truck and what configuration will stand the test of time. Step types, finishes, along with rigidity and structural integrity are all factors to keep in mind.

Location, Location, Location

So, you’ve picked a general style you like. Now, you need to consider the environment those side steps will be living in. Most side steps can be mounted to either the rocker panels or the frame, but the manufacturer will sometimes specify one over the other—especially if the mounting hardware is included in the package.

This is because frame-mounting side steps require longer mounting brackets. So even though the frame presents an extremely strong mounting location, those longer brackets can cause added stress. Additionally, on the frame, the bolts will be exposed to higher shear forces (caused by two opposing motions). Longer brackets make for higher leverage, which will increase forces on the hardware.

It’s important to note that with frame-mounted steps, you will almost never have to drill through the frame as they use the factory body mount positions. This also will have builders using the factory hardware, unless they opt to replace it. Though, whenever you are drilling, you want to be mindful of the fact that the area drilled will be bare metal. A quick coat of paint goes a long way in preventing the holes from rotting out down the line.

When mounting side steps to a rocker panel, the impression might be that this wouldn’t be sturdy enough; that the panels would bend. However, the steps are actually mounted to a steel plate up and under the passenger doors, essentially inside the vehicle’s body. So as long as the rocker panels aren’t rusted to death and the mounting brackets are high-quality, the rocker panels make for a strong mounting location.

Hardware Needs to Stand Up to the Test

So now that we have an idea of the kinds of forces the side steps will be exposed to, we can talk about bolt strength ratings and what makes them important to the conversation. Some of you may be thinking, “They’re just bolts, who cares?” But the truth is, bolts are actually pretty complex little pieces of mechanical engineering. Different styles (length, thread, coating, etc…) stand up better to different stresses. For our purposes though, we’re most concerned with graded bolts, specifically SAE American grading set by the Society of Automotive Engineers.

This grading system is used to determine the tensile strength of a bolt. Tensile strength refers to the force required to pull something to the point where it breaks. So for example, a Grade 2, low-carbon steel bolt has a tensile strength of around 74,000 psi, or pounds per square inch. And you can tell it’s a Grade 2 bolt because it has no markings on its head. As the number goes up, so does the strength of the bolt. Three raised dashes on the head refers to a Grade 5 with a tensile strength of 120,000 psi and six raised dashes marks the strongest commercial bolt, Grade 8, with a tensile strength of 150,000 psi.

The Shear Force of It All

So what does all this physics have to do with mounting side steps? It all comes back to those shear forces we talked about earlier. The fact is, higher carbon content will make bolts stronger, but it will also make them more brittle when exposed to shear forces. The thought of mounting hardware failing when too much weight is applied to a side step is already a scary thought. Can you imagine those bolts snapping while you’re driving? No thanks.

While common sense would lead us to believe that Grade 5 bolts will withstand shear better because they have a lower carbon content, we need to consider what’s the better choice when put to use on a side step.

The science-based answer?

A Grade 8 bolt has a higher yield strength than the tensile strength of a Grade 5 bolt. (Check out the chart above.) That means, the Grade 5 bolt will fail long before it has a chance to outshine the Grade 8 with its bending.

The non-science-based answer?

When I was a kid, I would hound my Dad with question after question about vehicles, and whether or not I should use something other than what the manufacturer provided while performing repairs. He would say, “Someone much smarter than me, who was paid a lot more than me, was tasked to figure this out. You should trust them.” While I’d argue there are a lot of circumstances when that logic could and should be challenged, in this particular instance it holds merit.

During my research, I found some hardware kits for both rocker-mounted and frame-mounted steps by CARR and Westin. And guess what was in them? Grade 8 hardware. That means that manufacturers—even of the steps you find on the roughest applications—opt for the superior tensile strength over any supposed gains in flexibility. Which makes sense, as shear forces aren’t as much of a threat as the stretching of a bolt is in this particular instance.

In our industry, it’s easy to overcomplicate things and second-guess yourself. As builders and hobbyists, questioning the “why” and proposing new ways to do things is part of the fun. Even if the information given has merit, it’s always better to do the research and form an opinion for yourself. Challenge what’s in front of you, like we just did, to find out why it’s the best approach and if there’s another way. This mentality will push you to think outside of the box and do things in a way that’s best for your particular project.

For those of you ready to challenge the status quo, make sure to join us in a couple weeks for our Tech Corner on fabricating custom hardware!