Bad company
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I am a Mechanical Engineer with a ton of experience designing shock isolation systems, and I own a 2010 Raptor. There are a few threads about the frame bending that happened on the Raptor Run, and talk of a weak point on the Raptor frame. I did an analysis on the stated conditions: 60 MPH, 18" tall "kicker" or dirt "speed bump" as a cause for this failure.
Below is my line of thought:
Ok, I ran some numbers, and they are eye opening.
Assumptions:
The "kicker" or "dirt speed bump" is one Raptor tire diameter accross, and is shaped like two ramps joined together (like a flattened triangle).
Case #1:
Kicker height is 18" (flattened to 12" by your tires)
Truck speed is 60MPH (88 fps)
The bottom of the tire has to move up 12" in .0166 seconds. this is an average speed of 60.24 ft/s
To generate this suspension speed, the truck would have to free fall 56 FEET!!!!! That's an impressive number, but what does it mean?
It means that the truck is recieving an impact equavalent to the first 12" of a 56 FOOT DROP WITH THE SUSPENSION ALREADY HALF COMPRESSED! My best guess is that the suspension acounts for about 6" of that, the tires for maybe another 3-4", the axle for some fraction of an inch, the truck vertical motion for another small fraction of an inch (no time to respond), and the rest? It all goes into deforming the frame by 1"-2".
This also tells me that even if the frame were boxed in that area, or if it was 3 times thicker, it would still bend. Even if the frame was reinfored enough to hold, the next likely point of failure is the axle, which would bend, stranding you.
Case #2:
Kicker Height is 12" (flattened to 9" by the tires)
Truck speed is 45 MPH (66ft/s)
The bottom of the tire has to move up 9" in .0221 seconds, an average speed of 33.94 ft/s vertical.
To generate this suspension speed, the truck would have to free fall about 18 feet! This is a MUCH less severe impact! More importantly, the impact is only 9" long (insert obvious joke here). Additionally the truck may be able to absorb it without requiring metal to deform.
The suspension can absorb 6", the tires their 3", the axle a tiny bit, the truck can move upwards a bit more, and all you probably have is tortured bump stops.
So those of you who have jumped their Raptors (and the most vertical air I've seen is maybe 8-9 feet) and said they don't have bent frames? This is because hitting an 18" kicker at 60MPH is about 7 TIMES as severe. PLUS your suspension is fully extended when you jump, cushioning the fall better, unlike the speed bump example.
Conclusion? If you hit something like a speed bump or "kicker" taller than your available suspension travel, plus tire "squash", at HIGH speed, you will bend metal.
The ONLY way to adress this issue is increase suspension travel to be greator than the intended acceptable "bump". Or god forbid (*sniff), slow down. Reinforcing the frame will either fail to work (bend anyway), or cause something else to fail (like the axle).
Nobody designs trucks to withstand those forces (like the first foot of a 56 foot drop with already compressed suspension), that would be incredibly impractical (and they'd sell one a year at $300k). I do not believe there is a design flaw, I believe that somebody found a situation that exceeds its strength.
I would love to join in the next Raptor Run, jumps are fine, short gullies are fine, just look out for the big kickers when you are burnin' up the dirt!
Below is my line of thought:
Ok, I ran some numbers, and they are eye opening.
Assumptions:
The "kicker" or "dirt speed bump" is one Raptor tire diameter accross, and is shaped like two ramps joined together (like a flattened triangle).
Case #1:
Kicker height is 18" (flattened to 12" by your tires)
Truck speed is 60MPH (88 fps)
The bottom of the tire has to move up 12" in .0166 seconds. this is an average speed of 60.24 ft/s
To generate this suspension speed, the truck would have to free fall 56 FEET!!!!! That's an impressive number, but what does it mean?
It means that the truck is recieving an impact equavalent to the first 12" of a 56 FOOT DROP WITH THE SUSPENSION ALREADY HALF COMPRESSED! My best guess is that the suspension acounts for about 6" of that, the tires for maybe another 3-4", the axle for some fraction of an inch, the truck vertical motion for another small fraction of an inch (no time to respond), and the rest? It all goes into deforming the frame by 1"-2".
This also tells me that even if the frame were boxed in that area, or if it was 3 times thicker, it would still bend. Even if the frame was reinfored enough to hold, the next likely point of failure is the axle, which would bend, stranding you.
Case #2:
Kicker Height is 12" (flattened to 9" by the tires)
Truck speed is 45 MPH (66ft/s)
The bottom of the tire has to move up 9" in .0221 seconds, an average speed of 33.94 ft/s vertical.
To generate this suspension speed, the truck would have to free fall about 18 feet! This is a MUCH less severe impact! More importantly, the impact is only 9" long (insert obvious joke here). Additionally the truck may be able to absorb it without requiring metal to deform.
The suspension can absorb 6", the tires their 3", the axle a tiny bit, the truck can move upwards a bit more, and all you probably have is tortured bump stops.
So those of you who have jumped their Raptors (and the most vertical air I've seen is maybe 8-9 feet) and said they don't have bent frames? This is because hitting an 18" kicker at 60MPH is about 7 TIMES as severe. PLUS your suspension is fully extended when you jump, cushioning the fall better, unlike the speed bump example.
Conclusion? If you hit something like a speed bump or "kicker" taller than your available suspension travel, plus tire "squash", at HIGH speed, you will bend metal.
The ONLY way to adress this issue is increase suspension travel to be greator than the intended acceptable "bump". Or god forbid (*sniff), slow down. Reinforcing the frame will either fail to work (bend anyway), or cause something else to fail (like the axle).
Nobody designs trucks to withstand those forces (like the first foot of a 56 foot drop with already compressed suspension), that would be incredibly impractical (and they'd sell one a year at $300k). I do not believe there is a design flaw, I believe that somebody found a situation that exceeds its strength.
I would love to join in the next Raptor Run, jumps are fine, short gullies are fine, just look out for the big kickers when you are burnin' up the dirt!
