A lot of those answers are based on feelings and not much real-world experience.
Fewer still are based on critical analysis of what a skid plate should do and how it should be designed.
I off-road a fair amount and have bent and broken sh!t on my bike that others haven't, so I'd say I'm hard on Urals.
I’ve broken a bike swingarm, a sidecar swingarm, hairline fractured my thumb, countless turn signals at all three corners, hammered the sidecar fender so many times it is permanently dimpled, bent two sets of handlebars, blown a final drive, dented the tub, tweaked front and rear fenders, broke the sidecar brake linkage bar, bent the stock left engine guard a dozen times, bent a raceway left side footbox and engine guard TWICE, etc. I've stopped counting how many times my bike has been on its side. With that off-road resume, my position on skid plates is this...
"99% of bikes don't need them despite what you might think. Most of those that get one, get one that at best is a useless farkle and at worse, is a false sense of security."
Now that everyone has their panties in a twist, hear me out on some things…
- Most bikes just don't really ride off-road. Some do, but MOST don't. and even those that do go off-road, they aren’t ridden very hard or over terrain or obstacles where a skid plate would make a difference.
- I'm going into my 9th year of off-roading with Urals. Never been on a ride where someone broke or has been hung-up by the oil pan or anything under the bike that a skid plate would have prevented.
- You can jack up your bike by the stock oil pan and it won't hurt a thing.
- I have dragged my oil pan over rocks, ruts and stumps, never came close to breaking it, put a few new shiny streaks on the fins, but that's it.
- I have only heard of a couple of people breaking an oil pan. Literally a couple…2 people. And one was in Moab and from what I understand, it was a pretty advanced trail. A place that 99% of Ural riders wouldn’t go and of the few who ride in Moab, most of them wouldn’t go.
- If you were really worried about being stranded with a broken oil pan, a spare oil pan and two quarts of oil fit in the trunk and are cheaper than a skid plate and you keep your ground clearance for the other 99.9% of the times you need it off-road. It just isn't an area of the bike that is a weak link. We don't have a "cracked oil pan" thread for a reason.
- The majority of the bikes I’ve seen doing Moab do not have a skid plate. A lot do, but most don’t.
The general idea is that you bolt a hunk of material to the underside of a vehicle to prevent damage to important parts and help the vehicle slide over obstacles. Faux skid plates AKA “Skid Fakes” are frequently bolted to vehicles for an off-road “look” but are not functional. We’ll discuss “Skid Fakes” in-depth later.
There are four factors to consider when determining the need for and design of a skid plate. (Technically it’s five factors, the fifth being “Tacticool” if you just want “the look.”)
- The first factor is the Vital Area(s) to be protected. On our rigs that is pretty much the oil pan and exhausts. Those are the only things that hang down low enough to make a skid plate worth the while. You could argue that the brake pedal linkage is important, but it is tucked up underneath pretty well. The center stand hangs down, but a skid plate would have to come back pretty far and be engineered to cover the center stand without interfering with operation. Not sure that is possible, nor is a center stand critical. So basically for our purposes, the oil pan and exhaust, with exhaust being the less critical of the two.
- The second factor is Clearance, both ground clearance and clearance between the skid plate and critical parts. You need to factor in whether the value of a skid plate is worth the decreased ground clearance. If the skid plate sustains a hard impact, what will happen to the components behind it? A skid plate that bends, deflects or is punctured will push against the components behind it.
- The third factor is Material thickness and appropriateness. This area, more than any other, separates the real skid plates from the ones that are just there for looks. It is also one of the most controversial subject when skid plates are discussed. Too thin and soft, it just gouges or bends, rather than remaining rigid and allowing the plate to pass over the obstacle. It might even fail completely and transmit force to the components behind it or it may tear loose and cause the vehicle to get hung up.
Skid plates on rock-crawlers and Baja vehicles use 3/16” steel or ¼” aluminum (usually 6061) to protect the parts they consider vital. You can argue that they are bigger and heavier vehicles thus need heavier materials. However a Ural has fewer points of ground contact and poor gearing so it generally needs to have more momentum in rocky terrain than Jeeps. I’d say those are appropriate metal gauges for a Ural with rider(s) flying over obstacles. And those thicknesses are for plates that are well fabricated, shaped and supported. The larger area you span the thicker or more support you will need. For a plate supported at the edges only, the strength is proportional to the thickness cubed. In other words, doubling the thickness will increase the load it can carry by a factor of eight.
Steel versus Aluminum
Given that some of the steel skid plates being sold are using 1/8” or thinner steel, which is inadequate to prevent bending, deflection and/or gouging, I am baffled by people who believe that they can use aluminum skid plates at similar thickness and they will be sufficient.
Yes, aluminum is generally stronger per pound then steel. The key there is “stronger per pound.” You will generally need to go with a THICKER piece of aluminum than steel to get the same properties, which will usually still be lighter than the steel it replaces.
For a main skid plate under the oil pan, I would say that 6061-T6 aluminum in ¼” thickness is the minimum to get a plate that will not deflect or severely gouge under a hard strike and allow the bike to slide over. In ¼’ thickness this material is stronger than most steel commercially produced Ural skid plates I’ve seen.
- The fourth factor is design. If the skid plate takes some big hits, where will that force be transferred? Will the attachment method be strong enough to keep the plate attached? Will the force be transferred to a bike part that may break/bend? Do you want the attachment points to fail as a type of “fuse” to help dissipate impact energy? How far apart are the attachment points? Can the material span these distances AND take an impact without deforming and deflecting? Can you use thinner material but add some bends to improve it’s rigidity? Will you have angled sections fore and aft to help slide over obstacles? How wide past the mounting points will the plate be to protect exhaust, etc? Can the material take a hit in these cantilevered areas?
A plate must handle forces in two major directions; upwards as the bike lands on an obstacle and rearwards as the leading edge of the skid plate encounters an obstacle. I’ve seen plates that use U-bolts on the frame uprights. Given the thinner material of these plates and the limits of clamping force, I have serious doubts about their ability to handle upward force and to a lesser degree, rearward force.
Some plates use only two or three mounting points. This is usually some combination of engine mounting bolts and clamps.
The strongest area of a bike is the rectangle formed by the frame, the engine mounts, the engine support rods, spacers and the engine itself. In that area the bike has to handle all of the weight the rest of the frame does, plus the engine forces, plus the weight of the rider standing on the pegs. It makes the most sense to tie into this area to mount the plate.
Still want a skid plate? OK. If you think your oil pan is at risk, despite all the evidence to the contrary, why would you cover it with a thin piece of sheet metal that is practically body panel gauge? Do you want a disposable skid plate, replacing it like fuses every time you bash something? Your most likely scenario that could cause damage (yet still a very unlikely scenario statistically speaking) is your front wheel going over something big, be it a rock, ledge, railroad rail or concrete drain pipe and your bike comes down hard on the skid plate.
Picture an experiment that goes like this;
Sling the frame of your bike at the steering neck and attach a quick release mechanism, then attach that to a chain hoist above the bike.
Lift the front wheel off the ground a few inches. I’ll let you keep the rear and sidecar wheels on the ground for this experiment.
Place a nice jagged rock with a flat base that is 1” taller than your ground clearance under your oil pan.
Now pull the quick release.
If that made you cringe at the thought, you are starting to understand the forces involved. And that experiment is with no rider and no momentum. Imagine coming down on an obstacle with 3 or more wheels off the ground, with a rider and a little speed.
Or if you are too squeamish to do this, instead put your skid plate in a sturdy vice and wail on it with an engineer’s hammer. Still cringe at the thought? Then you don’t have a skid plate. You have a SKID FAKE.
These are thin, useless pieces of metal bolted onto bikes out of a combination of misguided beliefs and the “cool farkle factor.” At best they are used because people figure “something is better than nothing.” But for the price they pay, a quality bulletproof skid plate could be bought/made.
Skid Fakes persist because of the simple fact that MOST Urals don’t need a skid plate so these things never get banged up. As a result they aren’t ever shown to be the useless hunks of metal they are. (Don't EVEN get me started about sidecar skid plates.)
Many commercial skid plates use material that is on the thin side. Why do they do this? Cost. Thin material is cheaper and thin material is easier to fabricate, namely when it comes to bending. Read that last part again. Thin material bends easily. If we want a skid plate to protect vulnerable areas, the one thing we DON’T want a skid plate to do is bend.
If you are going to catch a rock in that area, you want to just slide off unscathed.
You don’t want to crush your $$$ farkle, you don’t want it to gouge, rip off or damage some other part of the bike.
To date I have only seen one skid plate worthy of the name.
I believe only a plate built to the design and specs of COB's plate is capable of that.
There might be some other homebuilt plates (can't think of what is on Van's Baja at the moment and can't find the pics of his bike) that are equal.
But I guarantee you, anything you bought other than a COB plate is not up to the task.
If you are planning on hitting places like Moab or other rock strew areas on a regular basis, skid plates offer more than just protection, they can offer the ability to slide over obstacle rather than being hung up on them. Keep in mind that the skid plate needs to be the lowest point on the bike for this to be an effective terrain negotiation strategy. If you are dragging stock pontoons through the rocks, the skid plate becomes moot. You need to look at the underside of the bike and determine what is at risk to get snagged, eliminating as much as possible. Look at COB’s Predator build and how he cleaned up the underside of the bike by relocating exhaust, removing the center stand, extending the skid plate back to cover the transmission, etc.
So why am I writing all of this? Well I decided I wanted a skid plate, so I built one.
A damn sturdy one, if I may say so myself.