The Gun Counter

I saw some companies advertising these - frankly, I see the appeal of an Al bumper, but the Al skid plates seem counter-intuitive.

Is there a grade of Al suitable for such a purpose? What is that grade?

Anyone ever heard of "grade A" steel? (One of the companies claimed to use that - I suspect, like custom guns, this is an area with a shortage of engineering education.)

It seems like a thin sheet of a high-tensile steel could be comparable in weight to Al for equivalent strength.

Don't know the grade, but I used to always run an aluminum skid plate on my motocross/hare scrambles bikes. It saved the bottom end from rock damage more than a few times.

I would think 5000 or 6000 series AL would do just fine. Galvanic corrosion would be my main issue if it was being bolted up to something not AL.

Steamforger wrote:I would think 5000 or 6000 series AL would do just fine. Galvanic corrosion would be my main issue if it was being bolted up to something not AL.

We used to attach ours to the motorcycle frame with thick zip ties*. We would put a thick rubber grommet between the plate and the frame to absorb some energy from rock hits.

*Maybe not the best for auto applications. But there are other ways to isolate different metals.

The aluminum skid plates are getting to be popular among the rock crawling crowd. IIRC, they are using some fairly thick sections of 6061 aluminum. It's not what I would choose, a steel skid is going to be tougher and less subject to getting gouged by sharp rocks.

By grade "A" steel, they probably mean something like A36 steel, which is a standard grade of structural steel. Nothing special.

Properly shaped, and dimpled, Al skid plates can work fine. Although it depends on the planned use of the truck. Lots of trucks come factory with plastic skid plates and most off road race trucks use Al. Their main purpose is to prevent things from snagging or tearing at wires/hoses. If plans call for bouncing/sliding around on jagged rocks then steel is obviously a better choice as there is a better chance of something sharp punching through components.

Steel rusts. Aluminum doesn't. And it's going on the bottom of a vehicle to take through mud, creeks, etc., right?
We had a perfectly serviceable series of APCs (the M113) made entirely of aluminum armor. So unless you're planning on bouncing on rocks with more force than an RPG blast, Al plating would be perfectly serviceable. And an Al plate couold be thicker than steel, for an improvement in strength, or as-thick-as, for a weight savings. Or, if you're Scotty, you can make the aluminum clear, and carry humpback whales on board.

I wheel in a pretty corrosive environment, and I have never noted rusting of my steel skid plates to be a huge issue. Certainly, the steel body of the vehicle that the skids are attached to will rust away long before the skids do. And both steel and aluminum will corrode (steel corrosion being more commonly known as "rust") just fine, particularly when they are placed in contact with each other, in the presence of an electrolyte (water, mud, etc). As I said, the aluminum skid plates are becoming quite popular with the desert/rock crawling guys; they operate in an environment known for a distinct lack of mud and water to get into the interface between the steel and aluminum parts. In automotive restoration circles, "California car" is synonymous with being rust free.

Around here? I will keep my steel skid plates and bumpers. The paint and powder coating gets chipped, and they do rust... slowly. I do not expect my skidplates to become structurally compromised due to corrosion (rust) during the lifetime of the vehicle.

It's still a benefit, albeit minimal, leaving you only the weight/strength thing to get around.

I'm in California, and I'd choose steel simply because it can be welded in place far easier then bolting a slab of aluminum and worrying about dissimilar metals.

But for people who drive on roads where tons of corrosive salts are dumped, I could see where a plate of a much less corrosive material across the undercarriage would be an advantage, and not only from the sharp rocks.

Aluminum? Offroad? CA? Ayup. Friend has a real going concern here doing that.

Cheap? Not. Engineered, not just cobbled for looks.
Does a lot of custom work and also supplies Offroad RV builders (4x4 van conversion/safari type rigs).