Pros and Cons of the Skid Plates/Sump Guards you use

MiddleAgeSubie

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Dec 15, 2013
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990
Location
AZ
Car Year
2018 / 2008
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4Runner / Tribeca
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5EAT
I am unable to find a dedicated thread that discusses the pros and cons of specific skid plate models. This topic has engendered interesting discussions on the Foz forum. But there is no better place to list one's likes and dislikes about specific skid plates than here.

I have Primitive Triple Armor on my 2013 H6 Outback.

This combo consists of a large front plate (aka sump guard), second pic, a far from small middle plate that covers AT and the two CATs, Snapshot 2, and a smaller rear differential plate.

According to their website, the skid plates are made of 3/16" aircraft aluminum.

First of all, great many thanks to Primitive for designing and consistently providing aftermarket support to Subaru owners. This is greatly appreciated as their efforts are indispensable to make U.S. Subarus off-pavement worthy. Primitive also provides excellent customer service and they are happy to answer email questions about their products.

That said, none of us and no products are perfect. Here are my likes and dislikes about their skid plates.

WHAT I LIKE:

Fantastic on maintained unpaved roads and easy trails. The plates have beaten out tons of gravel and small stones that would have otherwise been bombarding the undercarriage. If it were not for the ubiquitous traces of Utah mud, LOL (and I do not go "mudding," just getting through from A to B with family on-board) you would think my car just came off the lot.

The plates got to "work" on three occasions. On the first one, I crested a bit too fast over an Outback and a half/two OBs in length but very steep hill. There is a trace of the hit right in the middle of the front edge of the skid plate, which yielded a bit. That's all.

On the second occasion, I misjudged a stone in water, rolling off it on the front and then AT plates. Some of the air openings in the front plate now show traces of the impact, i.e. are smashed, but that was that. Very happy.

On the third occasion, I fell into a rut that I simply failed to see, lol. The skid plates now show scratches in result.

Of all three occasions only the second really threatened the car. Nevertheless, the plates ensured my peace of mind and the undercarriage's clean and great looks. This car is still worth 29-30,000 and this definitely matters.

WHAT I DO NOT LIKE:

This is all about the front plate aka sump guard.

I cannot see how the AT plate could have been designed any better. It drops the clearance there by 0.5" under what is otherwise the car's lowest point, which is the connection of the exhaust tubes right behind the plate, but there is no way it makes sense to make the plate conform to AT and the super hot CATs. Indeed, I have had no issues in spite of our 6 months at over 100F. In addition, this plate is located entirely behind the front wheels which makes the loss of clearance minimal indeed. The rear differential plate leaves a lot of clearance. My differential is not dropped so I do not know the effects on vehicles with the subframe kit.

But the sump guard...

1/Loss of clearance. The sump guard, like the AT plate, becomes the car's lowest point, causing a drop of clearance of 0.5" compared to factory lowest point and more compared to original front-end clearance. The plate sits, obviously, ahead of the wheels and so low that it REQUIRES a compensatory lift (like mine, 0.5") to even make the Outback suitable for SOME moderate trails (adding 0.5" spacers means restoring the factory 8.7" of clearance). Since it is not easy to lift a Subaru more than an inch w/o getting into complications and/or compromises and since this definitely matters on a new car, the loss of clearance induced by the sump guard is very irritating.

2/Dubious heavy-duty utility. It has been plausibly argued on the Foz forum that this sort of sump guards cannot support the entire weight of the front end. Logically, then, a bad hit can shatter the skid plate right into the oil pan it is supposed to protect. The oil pan is far from the plate's support points and right above what seems to be a rather vulnerable spot.

Again, I am glad to have supported Primitive and by no means do I regret purchasing their front plate. Indeed, I am considering other of their products in the future. But, as I became a bit more experienced and eager to tackle rockier terrain, I am now inquiring into SubaXtreme's sump guard. This is supposed to be able to withstand heavier hits. I am now trying to understand the SubaXtreme plate's effect on ground clearance.
 
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Subaxtreme reduces clearance too, they all do.
Here are the differences:

Subaxtreme is airbag tested/approved and Australian Design regulation approved. Helps a lot here with insurances.

Subaxtreme is cast, alloy I believe.
This means it is a lot stronger, but is also more brittle. It can support the load of the vehicle better, and take scratches better but if there is ever an extremely big hit, they are known to crack.

Subaxtreme is reweldable, but not as bendable like aluminium ones.


My subaxtreme one is great, has some big gouges on it, and has support the weight of the vehicle many times. One of the side wings is a little bent, but that is from a side impact taking the weight of the vehicle. An aluminium one probably would have bent a lot more.
 
Thanks, Almostunseen,

but is the sump guard the lowest point of the car now, lower than the exhaust tubes that extend from the CAT(s) to the rear?

If it reduces clearance vis-a-vis the stock splash-guard but not as much as to get underneath the lowest point of the car, then that is great!
 
Gidday MAS

The photos you have posted don't really show the Primitive sump guard shape very well. However, it looks to me to have a gentler slope at the front than my SubaXtreme guard. However again, that could also be necessary because of the shape of the H6 engine underside.

I can't say what the clearance was before on Roo2, because the ABS plastic splash guard was already torn at the P/S front attachment bolt.

I just measured from the SubaXtreme guard to the ground, and that's 210 mm minimum. The rear bolts are attached through a recessed part, so do not protrude below the line of the guard. I am using 6 mm spacing washers front and rear to give plenty of clearance under my sump, both for additional leeway and also to provide plenty of clearance for my headers. I now have around 20 mm between the edges of the guard and the headers.

As mine had already had some bruising use, I used a small Canadian block splitter to bash it back into something like its original shape. This involved bashing it up to around half an inch from its shape when it came into my hands.

To my enormous surprise, it didn't even look like cracking when subjected to this cavalier treatment! I was rather pleasantly surprised at just how tough this guard is, considering that it's cast alloy. Given that you seem to be a careful and thoughtful driver, it should provide all the protection you need.

It sounds to me as if what you already have is doing the job for you. If it ain't broke, don't fix it! :poke:
 
You are right. I replaced the front plate pic with a clearer one that shows what it looked like when newly installed.

Ratbag, thanks for the 210 mm measurement! But I do not know your setup or the condition of your tires. So, my question is: how much clearance at lowest point of the car? Or, simply, is the sump guard the lowest point, which on my Subarus in stock form is on the exhaust tubes behind the AT (I am not counting any suspension components that may be nominally lower but go up with the wheels)? That's the 1,000$ question.

I am not considering raised springs etc until after this car has aged a bit. BUT I am exploring all ways to gain a quarter inch or half a centimeter here, a half inch or full centimeter there.
 
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On mine the sumpguard is about the same height as middle resonator now. I will check this arvo for you. My mufflers have had the hangers shortened so they don't hang as low
 
My SubaXtreme sump guard, now 11 years old, has withstood a lot of punishment through the years.
As a result it has a reasonable sized star shaped crack in it but still has good integrity.
I bashed the crack causing ding out with a hammer and no further cracking or failing took place then.
Can`t complain about it.
 
The lowest point of my exhaust (or anything else ... ) is about 195 mm. This includes measurements at the heat shields, centre flexion/gasket housing flanges and under the torpedo resonator in the rear pipe (not OEM, replaced it after the OEM one had one of the welds broken at Bunyip or Noojee).

My 5MT/DR gearbox is about 270 mm, and protected by the rear engine and rear gearbox cross-members that are about 200 mm. These are quite close together, so it would have to be something pretty nasty to get anywhere near the gearbox with any force.

Nothing else is lower than this, except the monocoque side rails under the floor pan. It appears to me that these are designed to scrape before anything else does.
 
Ratbag, great many thanks for this great info! :)

So, the sump guard seats a nice 15 mm or 0.5" ABOVE the vehicle's lowest point instead of 0.5" BELOW, as is my case.

Btw, you are telling me that you are stock, 195mm = 7.6", are you not? Or are your tires the reason you sit that low?
 
^ No worries, MAS.

Nominally, my car has 200 mm clearance. Nominally, this is 8 inches ... Apart from not having the SLS rears any more, it's as stock as a rock.

The problem arises when one looks at the OEM limits for the suspension height. The nominal OEM rear wheel centre to guard measurement for my car is (approx) 420-454 mms. This is NOT a small range.

Mine sits at 430 mm with the new Pedders heavy duty, variable rate springs and struts (new fully pre-built units), and a moderate amount of crap in the cargo area, second battery behind the P/S front seat. It pops up about 5 mm if I completely unload the car of the miscellany. So it is still around 20 mm less than the maximum OEM figure! The good bit is that with the trailer on with an 80 Kg ball weight, these only sit down about another 10 mm.

The above measurements are also not taken on the flat. The car is in the driveway, which has a downward slope of very approximately 3.5° towards the house, i.e. slightly nose down. This will have a slight effect on all these measurements, as will the fact that I am measuring from a brick paved surface using a tape measure and dodgy shoulders and elbows! IOW, it hurts ...

What all this crap basically means is that one should not take any nominal figure and try to translate this into something one can use in the field! I have done my best to remove little obstructions under my car where I can.

For example, turning my trailer electrical connector up the other way so that the mounting plate acts as a miniature protection plate, rather than it and the wires acting as a miniature grader! This is one of the most practical changes I have made to improve my clearance! Can you believe that? It was always dragging when coming over a sharp hump or coming out of a sharp dip. It doesn't do this anymore.

I also removed the spats from in front of the front wheels. I could see that they were a disaster waiting to happen.

The ABS engine bay protector already had one of the front bolts torn through, something I only discovered when I was about to fit my SubaXtreme sump guard. Like Ate, I bashed a star shaped crack (dented) back into flat, and nothing broke or fell off! I was equally as amazed as he was :biggrin:.

The underside now has no obvious catch points, except the spring loaded exhaust joint. However, I accept that it's not a Landcruiser ... When I pulled the transfer case out of my '68 LC, I could sit up under the truck to work on it ... :poke: :biggrin: :lol:.
 
Thanks, Ratbag.

So, everything makes sense now and we have determined that the SubaXtreme sump guard on your Foz does not lower the clearance of the vehicle. This is important.

You could not be any more right about the effect of terrain!

Just a small incline, like my driveway, causes a massive by Subaru standards improvement in approach angle and front-end clearance when pointing up, obviously. This--and the H6--is why I prefer to tackle any tougher terrain uphill, contrary to conventional 4wd wisdom. I have been over stuff that exceeds flat-level clearance when climbing (the rear has more clearance). I would not drive over the same stuff downhill, not without building the rocks anyway. The difference is not that huge as to make the exit impossible after a little work but obviously this works better on straight-through trails.

All of the above concerns an OB, of course, which has a particularly awful approach angle--and for no good reason (if a Foz can have several degrees extra AA, so can an OB; I get it that the very AWD Subaru layout limits the AA in the first place).
 
If it does reduce clearance by a little, you could always chuck some 1/4" spacers on to counter it.
 
MAS, I have never been able to understand why Subaru have hobbled the Liberty/Legacy, Impreza and Outback with such dreadful approach and departure angles.

When one gets underneath any of them, it is immediately apparent that this hobbling is all done by stuff that is almost all cosmetic. Unfortunately, it is very un-aesthetic if one removes it with a Dremel tool or angle grinder ...

Our SH is only as good as our SG because the SH has got an inch more nominal clearance. Again, the crap in the way is solely cosmetic. The nose is longer and closer to the ground than it needs to be.
 
ALMOSTunseen said:
If it does reduce clearance by a little, you could always chuck some 1/4" spacers on to counter it.
Click to expand...

That is one option, definitely, whether I get a SubaXtreme plate or not. The 1/4" can be added easily making it a total of 0.75 via spacers, since I have the 0.5" already. It is a stable lift, unlike the one obtained via tires.

The other option is to finally get a second set of wheels and tires. EDIT: deleted the rest on tires as out of place here.

Ratbag,

I think it is because for Subaru the only enthusiast crowd that matters is the WRX crowd. Maybe the FXT as well, but certainly in terms of road performance alone. I think that for them maintained dirt roads is the sum total of what they really mean by off-pavement.
 
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MiddleAgeSubie said:
Even with the 6 cylinder I may feel the loss of performance on very steep high elevation climbs (over 3,500 meters)
Click to expand...

Hasn't your car's engine got a MAF sensor in it? This should accurately compensate for the lower air density, unlike a MAP sensor.

EDIT: any separate set of wheels would be light-weight wheels in order to reduce the performance hit. The stock are about 21.5 lb, I think, and I could cut 5 pounds, just over 2kg, per corner via good aftermarket wheels.
Click to expand...

Are you sure about those weights? I have never weighed a bare rim on our SH (225/55 17" tyres), but I have from my SG (215/60 16"). IIRC, the steelies on it were around 11.5 kgs (25.3 lbs) and the alloys around 8 kgs (17.6 lbs), both naked ... :iconwink:.

Be very careful with aftermarket alloys. My insurer here has made it very clear that if I fit aftermarket rims of any description, it will almost certainly void my insurance. Even though we have very strict controls on these things here in Oz via the ADRs, etc. They are perfectly happy for me to fit any OEM alloys that will fit, just not any aftermarket ones. They must have a reason for this hard line stance, at least I would think so.

Ratbag,

I think it is because for Subaru the only enthusiast crowd that matters is the WRX crowd. Maybe the FXT as well, but certainly in terms of road performance alone. I think that for them maintained dirt roads is the sum total of what they really mean by off-pavement.
Click to expand...

I suspect that you are pretty right on the money with that comment. Certainly for the Liberty/Legacy, Impreza and OB. The Forester has pretty decent approach, departure and hang angles, considering that it still drives more like a racing car than anything else ... :lildevil:.

My SG isn't quite as good at tight high speed handling as my Impreza was. It makes up for the higher centre of gravity and thus body roll a bit with far superior engine power/torque and far better gearing, but there is just no way I would throw it into a marked, known 50 kmh corner at 90 kmh the way I did my Impreza last time I was in Brisbane in 2011. The corner in question is one that I have been familiar with since around 1964 ... Probably happy to try it at 80 kmh though ... :lildevil:.
 
I wrote a long post and then deleted it before posting; I also edited the one above. This thread is about skid plates, after all; let's leave the tire discussion for later. ;) Mea culpa.
 
OK, I took another look with the car up high for an oil change at the dealer. There isn't much distance between the primitive sump guard and the exhaust. Probably they wanted to have a bit of air in there rather than make the plate be within mm of the tubes. Then the exhaust veers up sharply, at which point the plate goes up, as well. It is maybe there that it could have saved some air at a critical spot. But I may have been a bit harsh above. Maybe there is no way to make the plate more than just a bit tighter fit.

I am still curious about the SubaXtreme plate. They have a Facebook pic of an OB with it that makes no sense to me and does not match what they told me by email. Confused.
 
^ I had to belt the crap out of my s/h one, and make up some spacers out of 2-2.5 mm washers for the front and rear to stop it rattling badly on the exhaust heat shields.

Now it's as quiet as a pussycat :) :biggrin:.
 
My crossbred one needed a fair bit of grinding to stop it hitting the exhaust. As well as filing out the holes so it fit, but i think that is more my beaten up cross member than the plate.
 
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