I ran on to this some time ago and I have not done the weights and measurments on my own FJ but soon will.
I thought it best to share this with those of you that are pushing the envelope of your FJ and those of you that are not, just in case you might want to and do it with relative safety.
Knowledge is a great thing to have, no matter where it comes from.
I offer you this link to one of the best articles I have yet to read on the subject of Roll-Over.
One thing to remember is that the forces acting upon a vehicle also include those due to acceleration or deceleration in addition to gravity and friction.
So if you are in a situation where you are stable on a hill in a static condition, that is to say your center of gravity is within the rectangle described by the projection of your wheelbase onto a horizontal plane, you will be in a no rollover condition.
However, you can be on that same hill and be going down it, for example, at the same angle, and then, for example, slam on the brakes. This has the effect of moving your "center of gravity" forward with respect to the horzontal projection of your wheelbase, and could cause the center of gravity to move forward of your front tire patch and throw you into a endo.
Technically, the center of MASS does not move forward, but the center of FORCE does, and the article talks about the center of gravity, which is the center of force in a static condition but not in a condition of acceleration or deceleration. So if braking, acceleration or spring bounce cause your center of force to move out of the rectangle, you will be in a roll condition, even if your center of mass is within the rectangle.
So in other words if you do all the measurements and calculations and come up with numbers for your rollover angles, an additional margin has to be added to allow for the dynamic conditions associated with braking, acceleration, and spring bounce. ALso there is the error introduced by forces associated with gasoline sloshing and passenger overexcitement.
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BCMT6, Pkg2, KOs, rack, rails, hitch, Abrams, I-Way, Baja 480C, 150W maplight, aux backuplights, aux battery, gerrycan rack, dead buzzers/DRL
One thing to remember is that the forces acting upon a vehicle also include those due to acceleration or deceleration in addition to gravity and friction.
So if you are in a situation where you are stable on a hill in a static condition, that is to say your center of gravity is within the rectangle described by the projection of your wheelbase onto a horizontal plane, you will be in a no rollover condition.
However, you can be on that same hill and be going down it, for example, at the same angle, and then, for example, slam on the brakes. This has the effect of moving your "center of gravity" forward with respect to the horzontal projection of your wheelbase, and could cause the center of gravity to move forward of your front tire patch and throw you into a endo.
Technically, the center of MASS does not move forward, but the center of FORCE does, and the article talks about the center of gravity, which is the center of force in a static condition but not in a condition of acceleration or deceleration. So if braking, acceleration or spring bounce cause your center of force to move out of the rectangle, you will be in a roll condition, even if your center of mass is within the rectangle.
So in other words if you do all the measurements and calculations and come up with numbers for your rollover angles, an additional margin has to be added to allow for the dynamic conditions associated with braking, acceleration, and spring bounce. ALso there is the error introduced by forces associated with gasoline sloshing and passenger overexcitement.
I understand what you wrote (I think). But, damn, my head hurts just reading it.
He's talking about momentum. The key is to go very slowly and don't make any sudden changes in speed (faster or slower) or direction that will cause your momentum to carry you outside the rectangle.
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Stock TRD SE with M/T and bling aluminum front skid plate
Location: currently Huntsville, AL, originally from Honolulu
Posts: 1,696
Re: Center of Gavity and Your Safety On The Trail
knowledge = power = safety. Gotta know your limits. All about working smarter not harder. Although I'll admit all this number crunching and measuring makes my head hurt.
One thing to remember is that the forces acting upon a vehicle also include those due to acceleration or deceleration in addition to gravity and friction.
So if you are in a situation where you are stable on a hill in a static condition, that is to say your center of gravity is within the rectangle described by the projection of your wheelbase onto a horizontal plane, you will be in a no rollover condition.
However, you can be on that same hill and be going down it, for example, at the same angle, and then, for example, slam on the brakes. This has the effect of moving your "center of gravity" forward with respect to the horzontal projection of your wheelbase, and could cause the center of gravity to move forward of your front tire patch and throw you into a endo.
Technically, the center of MASS does not move forward, but the center of FORCE does, and the article talks about the center of gravity, which is the center of force in a static condition but not in a condition of acceleration or deceleration. So if braking, acceleration or spring bounce cause your center of force to move out of the rectangle, you will be in a roll condition, even if your center of mass is within the rectangle.
So in other words if you do all the measurements and calculations and come up with numbers for your rollover angles, an additional margin has to be added to allow for the dynamic conditions associated with braking, acceleration, and spring bounce. ALso there is the error introduced by forces associated with gasoline sloshing and passenger overexcitement.
Excellent post, especially when taken into concert with MoSun's info. However there is one other dynamic factor that seems to have been left out of the equation, and that is the 'shifting' or 'loose' load. When edging close to the maximal tolerances of a vehicle allowable under the mathmatical calculations, one must consider the sudden shift of a loose load in the cargo area, passengers, or fuel!
Loose loads, or liquid loads, can add hundreds, sometimes thousands, of foot pounds of force, even if there is no overt deceleration or acceleration applied. Such loads are often subject to 'harmonic' forces. In other words, consider the effect of 10 gallons of fuel (60 pounds) reverberating laterally or vertically upon a wash board road. This particular force often gets tanker truck drivers (even with internal tank baffles) into very serious trouble. For the four wheeler, the 'rebound' effect laterally as he negotiates a 'left-right' situation may be just the lynch pin dynamic that pushes his vehicle past the point of no return.
- Chris 
Linear Mode
