When it comes to outfitting your off-road vehicle for adventure, skid plates are an essential piece of armor. Different OEMs provide different levels of protection for the undercarriage, which could change by model, trim level, and even model year. Aftermarket skid plates provide protection from rocks, debris, and unforeseen obstacles that can turn a thrilling trail ride into a costly repair bill.

A crucial decision off-road enthusiasts face is what type of material to choose for their skid plates: steel or aluminum. The answer is actually more nuanced than most people think: there are different types of aluminum and steel, and each could be better for different components based on the protected component and the skid plate design. Understanding these differences is key to making the best choice for your vehicle and driving style.

In this article we won’t consider plastic skid plates (also known as HDPE, high-density polyethylene). Though like aluminum and steel, there are different types of plastics, in general even the strongest plastic skid plates will provide a lot less protection than a basic metal skid plate.

How does the protected component affect the required material?

Vehicle undercarriage components are not all created equal.

The differential and control arms sit low to the ground. Therefore, they are highly likely to impact rocks and other debris. These components also have a relatively small surface area. This means they require protection from a material that is as strong as possible, and the difference in weight will not make a meaningful difference. Therefore, in most cases, it’s preferred to use steel to protect the differential and the control arms.

Other components in the vehicle's undercarriage are much higher off the ground. They also have a much larger surface area. Examples include the engine, transfer case, and exhaust. These components require large plates with good coverage around the edges to protect the entire component. Since the plates protecting these areas will be much larger, the choice between steel and aluminum will have a much more substantial impact on the overall weight of the skid plates.

How does the choice of materials affect the design and building of skid plates?

The material chosen for the skid plate is an important factor in design and manufacturing. Steel and aluminum have different strength profiles, requiring them to be welded, cut, and heat-treated differently. Sheets of steel and aluminum also come in different sizes and gauges from suppliers, which also affects the manufacturing process.

Some skid plate manufacturers simply take an existing design in steel and try to recreate it in aluminum, adding or removing some strengthening elements or welds. This results in weaker design and strength compared to a skid plate designed for a specific material from the start.

For example, a skid plate made from aluminum, designed from the start to work with its specific material properties, can perform better than a steel skid plate with a poor design.

It is recommended to ensure that the skid plates were designed for their material from the start.

What is the typical weight difference of aluminum and steel skid plates?

In general, expect a 50% weight difference between steel and aluminum.

For example, for the Wrangler JL, expect a complete aluminum belly pan skid plate set to weigh around 100 lbs, while the equivalent skid plates made out of steel will weigh around 200 lbs.

This difference in weight is significant.

Given a Wrangler's payload capacity is roughly 1000-1200 lbs, the difference between aluminum and steel skid plates is almost 10% of the usable payload of the vehicle!

The additional weight  Impacts many aspects of the vehicle performance:

• Installation: Increased weight translates to more difficulty installing the skid plates in a DIY setting. It is more difficult to lift and position a 40 lbs plate then a 20 lbs plate.

• Fuel Economy: Increased weight translates to reduced fuel efficiency, which can be a concern on long trips or expeditions.

• Suspension Wear: The added mass puts additional strain on the vehicle's suspension components, potentially leading to faster wear and tear on shocks, springs, and bushings. This might even require a suspension upgrade to compensate for the additional weight of a full set of steel skid plates.

• Recovery: A heavier vehicle can also be more challenging to recover if it gets stuck.

How do steel and aluminum skid plates differ in corrosion resistance?

Aluminum naturally forms a protective oxide layer when exposed to air, making it highly resistant to rust and corrosion. This is a major advantage in wet climates, coastal areas, or environments where road salt is prevalent. Aluminum skid plates will maintain their aesthetic appeal and structural integrity for longer without the need for extensive anti-corrosion treatments.

Steel skid plates will require constant maintenance and paint touch-ups to prevent rust formation. In extreme cases, a rusty skid plate could even become brittle, providing little to no protection.

Do skid plates necessarily require the strongest and toughest material?

If the skid plates hit a big, hard rock at speed, or the vehicle skids on hard rock surfaces, the properties of the skid plate material could determine how much damage will be caused to the vehicle itself.

While steel skid plates will dent less because they are stronger, they will not absorb the impact but will transfer the forces to the vehicle's chassis. The vehicle's chassis is designed by the OEM to flex just a little bit when reaching extreme situations. If the skid plates increase stiffness and transfers additional forces to the chassis, long-term damage to the chassis and frame can occur. In contrast, aluminum skid plates absorb some of the energy from impact, reducing strain on the chassis.

In the short term, aluminum skid plates may seem more scratched and dented than steel skid plates, but that is a sign they are doing their job correctly by absorbing energy from extreme hits.

Based on your off-roading characteristics, should you pick aluminum or steel?

For small components that aren't close to the ground such as the differential and control arms, Steel components provide a good balance of strength and weight. 

For larger components in most of the underside of your vehicle, it's essential to identify your primary off-roading characteristics.

Here are some common "types" of off-roaders and their typical use cases:

Other Additional considerations:

• Vehicle Weight: Heavier vehicles like full-size trucks or SUVs might benefit more from aluminum to offset overall weight, while lighter vehicles might not see as dramatic an impact from steel.

• Climate: If you live in a region with high humidity, frequent rain, or use road salt, the corrosion resistance of aluminum becomes a more compelling factor.

• Maintenance Willingness: Are you prepared to regularly inspect and potentially touch up steel plates to prevent rust?

• Interest in DIY installation: For those interested in installing the skid plates independently, aluminum should be considered for its lighter weight, making it easier to handle in a driveway with simple lifts.

Summary: for almost all skid plate use cases, aluminum is supreme

Choosing between steel and aluminum skid plates for off-road vehicles involves considering material properties, protected components, design, weight, corrosion resistance, and driving style.

For almost all use cases, aluminum is the more practical choice thanks to its good protection, lower weight, corrosion resistance, and energy absorption. Steel skid plates also have their uses, but they are ideal only for smaller components, or for highly intensive rock crawling in dry climates.