skid plates?
- Thread starter TEETS
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FortyMileDesert
Adventurer
Don't forget PICKING THE RIGHT LINE and crossing the obstacle SLOWLY. That generally requires very minimal and light weight skids.
I've got .125 wall 2" x 3" rectangular aluminum tubing for sliders, .25 thick aluminum plate for front and gas tank skids, NO transmission or transfer case skids, NO differential guards, stock plastic front bumper, 3 pieces of laminated 2x4 douglas fir for a rear bumper - - and my rig has survived over 100 off-road treks with minimal damage....
Your greatest off-road protection is driver skill, experience, maturity and patience..............:26_7_2:
I've got .125 wall 2" x 3" rectangular aluminum tubing for sliders, .25 thick aluminum plate for front and gas tank skids, NO transmission or transfer case skids, NO differential guards, stock plastic front bumper, 3 pieces of laminated 2x4 douglas fir for a rear bumper - - and my rig has survived over 100 off-road treks with minimal damage....
Your greatest off-road protection is driver skill, experience, maturity and patience..............:26_7_2:
goodtimes
Expedition Poseur
Metcalf brings up a good point. There generally isn't a need to cover every component in 3/4" steel plate. There are certain items that should be guarded in a serious fashion, and others that really don't need it.
For example, lets look at my '03 wrangler, specifically the gas tank skid plate, and the t'case skid plate. They are both stamped steel, 11ga (1/8") from the factory. The t'case skid is right in the center of the vehicle, the gas tank is all the way at the rear end, behind the rear axle. Both hang really low and are very easy to hit/catch things (rocks). I spend time on trails that are significantly more difficult than probably most people on this board.
70K miles after purchasing the jeep (new), the gas tank skid is still right where it was put by the manufacturer. It is bent, has rock rash, and generally has seen better days, but it is still in place, and still functioning. The t'case skid was mangled so bad that it had to be replaced. It was bent up so far that I had trouble keeping the transmission in 1st/3rd/5th gear because the shift lever was hitting the console. I had bent it so bad the t'case was pushed strait up about 3".
Both of the plates are of similar size, unsupported on 2 sides, and were drug over the same rocks. Why did the gas tank skid live and not the t'case skid? One of the biggest contributing factors is the location on the jeep. The t'case skid plate supports the entire weight of the jeep if you are high centered (yes, this is an extreme example, but it helps to visualize my point). The gas tank skid supports only 1/2 of the vehicle weight, because the front tires are supporting the other half (again, not a perfect example, but you can see the point). Additionally, the gas tank skid plate is not likely to take a huge impact load due to it being located behind the rear axle, which hangs lower than the skid plate, and is just inches forward of the tank. The axle helps protect it. The t'case skid does not have the same protection, so it is more likely to get hit from the front. The end result? OEM gas tank skid still in place, OEM t'case skid is in a junk yard somewhere, and has been replaced with ~ 8 sq/ft of 1/4" steel plate.
There are other factors that do play into this, but I'm sure you can see my point....some areas are more likely to be damaged than others, for a variety of reasons. With the light weight rigs most of us use (less than 10K gross weight), there isn't much payload available to give up to skid plates. Scott Brady's tacoma is running at, or just over GVWR, with minimal skid plates. Adding 3 or 400 pounds of additional steel plate (which is easy to do) would have a large, negative, effect on his trucks performance. Selective use of different materials and careful consideration of size/shape/placement of skid plates is pretty essential if you wish to retain a fair amount of your payload on light vehicles....which you need to do if you want to carry alot of gear. There are compromises to be made...costs and payoffs for each. Which way you lean really depends on the trails you spend time on, your driving style, how much payload you can afford to give up to skid plates, and you much gas you want to buy over the long haul.
For example, lets look at my '03 wrangler, specifically the gas tank skid plate, and the t'case skid plate. They are both stamped steel, 11ga (1/8") from the factory. The t'case skid is right in the center of the vehicle, the gas tank is all the way at the rear end, behind the rear axle. Both hang really low and are very easy to hit/catch things (rocks). I spend time on trails that are significantly more difficult than probably most people on this board.
70K miles after purchasing the jeep (new), the gas tank skid is still right where it was put by the manufacturer. It is bent, has rock rash, and generally has seen better days, but it is still in place, and still functioning. The t'case skid was mangled so bad that it had to be replaced. It was bent up so far that I had trouble keeping the transmission in 1st/3rd/5th gear because the shift lever was hitting the console. I had bent it so bad the t'case was pushed strait up about 3".
Both of the plates are of similar size, unsupported on 2 sides, and were drug over the same rocks. Why did the gas tank skid live and not the t'case skid? One of the biggest contributing factors is the location on the jeep. The t'case skid plate supports the entire weight of the jeep if you are high centered (yes, this is an extreme example, but it helps to visualize my point). The gas tank skid supports only 1/2 of the vehicle weight, because the front tires are supporting the other half (again, not a perfect example, but you can see the point). Additionally, the gas tank skid plate is not likely to take a huge impact load due to it being located behind the rear axle, which hangs lower than the skid plate, and is just inches forward of the tank. The axle helps protect it. The t'case skid does not have the same protection, so it is more likely to get hit from the front. The end result? OEM gas tank skid still in place, OEM t'case skid is in a junk yard somewhere, and has been replaced with ~ 8 sq/ft of 1/4" steel plate.
There are other factors that do play into this, but I'm sure you can see my point....some areas are more likely to be damaged than others, for a variety of reasons. With the light weight rigs most of us use (less than 10K gross weight), there isn't much payload available to give up to skid plates. Scott Brady's tacoma is running at, or just over GVWR, with minimal skid plates. Adding 3 or 400 pounds of additional steel plate (which is easy to do) would have a large, negative, effect on his trucks performance. Selective use of different materials and careful consideration of size/shape/placement of skid plates is pretty essential if you wish to retain a fair amount of your payload on light vehicles....which you need to do if you want to carry alot of gear. There are compromises to be made...costs and payoffs for each. Which way you lean really depends on the trails you spend time on, your driving style, how much payload you can afford to give up to skid plates, and you much gas you want to buy over the long haul.
Bob_Sheaves
Observer
As an OEM design engineer, I do this "stuff" all the time. Without determining the loading the vehicle is going to see, saying "do not underestimate the importance of light weight" is meaningless and ignores the fact that aluminum is NOT lighter than steel, when strength is designed in.Metcalf said:
The most cost effective material is, 9 times out of 10, steel. You are, of course, free to do what you think is right and can afford. On all objective (key word there- "objective") counts, a strictly economic versus performance tradeoff study shows that steel wins hands down. It is inexpensive, has a high modulus, thin cross section for weight, is easily formable, and requires minimum skill on the part of the fabricator to build an acceptable part, due to no exotic equipment or techniques are involved.
Best regards,
Bob Sheaves
CEO
catNET Incorporated
http://www.catnetsolutions.com
Bob_Sheaves
Observer
None of those materials work for skid plates that are either affordable, or functional with a Dodge pickup. Did you not understand the meaning of the 21G force I mentioned earlier? Please ask if I do not explain something completely for complete understanding of what is involved.Metcalf said:
Best regards,
Bob Sheaves
CEO
catNET Incorporated
http://www.catnetsolutions.com
Bob_Sheaves
Observer
Exactly my point on the Jeep plates. When they were designed, 21G was used, same as I mentioned earlier in the Dodge, as the point loading on the plates. Gross mass of the plate was inconsequential to the thickness, as this "vehicle mass x impact accelleration" will simply show that the Dodge develops greater energy applied to the structure and plate, when compared to the Jeep.goodtimes said:
ADDENDUM:
Be careful with the words "different materials". As was stated before-with proper design, steel is no heavier than aluminum among others.
Best regards,
Bob Sheaves
CAO
catNET Incorporated
http://www.catnetsolutions.com
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goodtimes
Expedition Poseur
Bob, you seem to really dislike aluminum, favoring steel in every response to this thread. Any particular reason?
Personally, I like steel because it is much easier for me to work with steel, and I'm cheap (I'm easy too.. :sombrero
.
I suspect in many cases, people who are using alternative materials (aluminum, fiberglass, etc) are doing so as much for personal experience as for material advantages. I know this is true on my own projects....I might build a widget out of fiberglass just because I have never worked with fiberglass before...steel may be just fine..but hey, it's fun to experiment with new materials. Other than the cost issue...any reason to NOT use aluminum or other alternatives (assuming the chosen material is up to the task)? Afterall, we are talking about one-off parts...not mass production.
Personally, I like steel because it is much easier for me to work with steel, and I'm cheap (I'm easy too.. :sombrero
. I suspect in many cases, people who are using alternative materials (aluminum, fiberglass, etc) are doing so as much for personal experience as for material advantages. I know this is true on my own projects....I might build a widget out of fiberglass just because I have never worked with fiberglass before...steel may be just fine..but hey, it's fun to experiment with new materials. Other than the cost issue...any reason to NOT use aluminum or other alternatives (assuming the chosen material is up to the task)? Afterall, we are talking about one-off parts...not mass production.
Bob_Sheaves
Observer
I am against anything exotic for a number of reasons, not the least of which is that steel is the most economical, highest performing material for use in any vehicle for structural purposes.goodtimes said:Bob, you seem to really dislike aluminum, favoring steel in every response to this thread. Any particular reason?
Personally, I like steel because it is much easier for me to work with steel, and I'm cheap (I'm easy too.. :sombrero
I suspect in many cases, people who are using alternative materials (aluminum, fiberglass, etc) are doing so as much for personal experience as for material advantages. I know this is true on my own projects....I might build a widget out of fiberglass just because I have never worked with fiberglass before...steel may be just fine..but hey, it's fun to experiment with new materials. Other than the cost issue...any reason to NOT use aluminum or other alternatives (assuming the chosen material is up to the task)? Afterall, we are talking about one-off parts...not mass production.
Additionally, in the case of an exploration rig, there is the "whoops" factor and necessarily unavoidable field repairs. I can almost guarantee that there will not be a heliarc around to repair a titanium or aluminum structural member in the middle of the Saharan desert, unless the Dakar is running (then you have to beg-been there, done that, broke, and had to beg...hehehe) and damn sure no carbon fibre available for repairs. A servicable weld (ADDENDUM: "in mild steel") may be made by shorting across a pair of 8D truck batteries and a couple of wire coathangers to get you to the next town. Been there also....
One off parts are even more important for serviceability and repair in the field. You can't have FedEx deliver a new part overnight when none exist, so being able to repair your truck in the field has an even greater importance.
Best regards,
Bob Sheaves
CEO
catNET Incorporated
http://www.catnetsolutions.com
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Bob_Sheaves
Observer
21G's is the military value (and also used by Jeep /Truck engineers) for the impact force applied in various vectors to the vehicle components when designing skidplates, frames, mountings, etc. You are quite correct in the actual formula-short form is "mass x 32ft/sec/sec" This resultant is the initial impact the material must deflect, absorb, and not deform permanently against. Any material will bend, the only questions are "how far will it deflect without permenant deformation (bending and not springing back into it's original shape)" and "what is the ultimate breaking point of the material".goodtimes said:
The modulus of elasticity of a material will tell you how much elongation will occur before permanent deformation. Aluminum, by weight, is a piece of cardboard compared to steel. As stated before it takes 3 times the mass of aluminum to obtain an equal modulus of steel. In simpler terms, it DOES take a piece of 1.13 inch thick aluminum to equal the stiffness of a 3/8 inch thick piece of steel. The weight of the 2 materials will be the same, for the same stiffness.
ADDENDUM:
Example-take 2 pieces of materials, one steel and one aluminum, in 1/4 inch thickness and 12 inches square. Now apply a load to the exact center of each plate (the same load value). The aluminum plate will deflect 3 times as much as the steel. Practical meaning......overcenter on a piece of granite-you now have the deadweight of the truck being applied to the skidplate. With the aluminum plate, you must have 3 times the clearance between the inside surface of the plate to the transfer case for the aluminum material, when compared to the steel plate. This extra clearance means that the aluminum plate must hang down farther from the frame to keep from breaking any parts-like the aluminum case of the NVG241OR-and INCREASING THE LIKELYHOOD of an overcenter, when the steel can be thinner, and tucked up under the vehicle higher from the ground, yet not bend and hit the t/case housing.
Best regards,
Bob Sheaves
CEO
catNET Incorporated
http://www.catnetsolutions.com
Last edited:
Bob_Sheaves
Observer
Yes, TACOM (Tank Automotive and armaments COMmand-US Army) developed the number in the early 1950's during the first "soft" vehicular air drops. 21G represents the peak force acting on a vehicle when it is dropped out of an aircraft, by parachute.goodtimes said:
Best regards,
Bob Sheaves
CEO
catNET Incorporated
http://www.catnetsolutions.com
Bob_Sheaves
Observer
Jeep was involved with the original M38/M38A1 series development vehicles for a number of years. The 21G loading, as well as VCI (not that silly "ramp index" garbage) made the move to Jeep CJ's from the military world (the same people designed both military Jeep's and Civilian Jeep vehicles, up untill the advent of AM General).goodtimes said:
BTW- VCI=Vehicle Cone Index, which is a far truer identifier of offroad mobility than any silly magazine's "ramp index" test.
Best regards,
Bob Sheaves
CEO
catNET Incorporated
http://www.catnetsolutions.com
Last edited:
goodtimes
Expedition Poseur
Hmm...so it was just a carry over when the designers moved on to CJ's, and it has been used ever since.
But RTI ramps are quite useful for increasing the amount of grunting and knuckle dragging among the "hold my beer and watch this" croud. Oh, they're kinda handy for figuring out if your bump stops are to damn short.
But RTI ramps are quite useful for increasing the amount of grunting and knuckle dragging among the "hold my beer and watch this" croud. Oh, they're kinda handy for figuring out if your bump stops are to damn short.