Quote:
Originally Posted by jkd
Oh yea? Let me get my ATV on my ramps and then have you try to lift the rear of the ramps off the ground. You might want to rethink that one, driving up the ramps even with the front ATV axle on the tailgate, Mother Earth is still supporting a good part of the load.
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I misused the word "All", but there is still a great deal of load on the tailgate that would otherwise not be there.
You have the force of the weight of the ATV. For arguments sake, we'll say the ATV weighs 800lbs with you on it (600lb ATV, 200lb rider) and the CG is such that the weight is evenly split on the F/R axles (400lb each). The force B is 400lb, loaded approximately 2/3 the way up the ramp. We can also assume the ramp angle C is 30 degrees. The rear axle load B then is distributed between the resultant force D ("mother earth") and force E (the tailgate or that product). We can break force B into it's components, and when doing so we find out that the force perpendicular to the ramp is ~350lb. [ 400*cos(30) ]. Since that force is 2/3 the way up the ramp, we need to force balance the loaded member. There is a component of force D and E supporting this weight. According to Newton, the sum of the moments on any loaded member equals zero around any given point. If we analyze the moments around the point where the ramp touches the ground we have a moment of 400lb x 2L/3 and another equal and opposite moment of xlb x 3L/3. 267L = xL, the L's cancel, and we have a force of 267lb on the gate perpendicular to the ramp. The component of this force acting downwards is 308lb ( 267/cos(30) ).
Considering the rear axle load assumption of 400lb on the ATV, I would say that 308lb on the gate is a very good deal of additional stress that could cause cracking.
I made a lot of assumtions in this calculation, but the gist is there...