[daless2]

Originally Posted by Sanosuke

One minor thing you missed -- the weight of the ramp itself, otherwise a good explanation. How about force per sq inch exerted on the tailgate at the lips at the top of the ramp? This is the primary concerning force for causing the tailgate to display stress fractures.

I'll be posting actual figures when I do some measurements in the real world using *one* ramp as one-half of the representative weight. I have a Polaris sportman 400 quad and a heavy steel ramp for it so I'll go ahead and measure the height of the top lip of tailgate to ground and then measure the angles out for you. This would only be representative of the actual ramp I use to load my dirtbike (A '04 Honda XR250R at about 250 pounds w/full tank) however.

Update:
7' ramp extended towards a 33.55" height, gives me a 23.54 degree angle. With a 250 pound dirtbike w/front tire on tailgate and rear tire off, the force exerted downwards, at the top of the tailgate this would be 270 pounds, with two ramps this would be a whooping 540 pounds if loading two bikes simulateously. IF loading my polaris quad which weighs in around 500 pounds, this would be 545 pounds distributed across two ramps exerting onto the tailgate or 272.50 pounds on either ramp pushing on the tailgate. The pressure applied on the tailgate is even more significant given the little surface area of the bolt that presses down on the tailgate (think of it as a finger pressing down on a ledge and you have the lip design of my loading ramp). These figures would be compounded with the extra weight of the ramp resting on the tailgate's lip. You get the good idea of the pressures involved in causing our tailgates to crack at the seams.

Sanosuke!

Negative, my friend, this simply is not correct.

I believe there is a major flaw in your calculations as this goes against basic laws of physics.

A 250 pound bike, with the front tire on the tailgate, and the rear tire on a 7 foot ramp, and a ramp angle of approx 23.5 degrees really can’t be putting much more then 103 pounds of weight on the tailgate in that position. Can’t calculate it out exactly without knowing the wheelbase of the bike.

There is no Physical way for the weight to exceed 100% of the total weight, without cantilevering, which isn’t in play when one end of the ramp is sitting on the ground.

I apologize in that I do not wish to come across as being a jerk to you. I really do wish to be helpful. Perhaps I can try to simplify this to my own minds level.


Instead of a Bike, let’s use a Unicycle, one wheel.

And instead of a ramp on an angle, let say it is a horizontal ramp, one end on a sawhorse, one end on the tailgate.

For easy math lets say the ramp is 10 feet long too.

This will allow an explanation without the complexities of multiple wheel (load) locations and angle of assent. We can just focus on weight distribution.


If the Unicycle weight 200 pounds, and it is sitting on the ramp, right on top of the sawhorse, then 100% of the weight, 200 pounds would be sitting on the sawhorse end of the ramp, and no weight (other then the ramp itself) would be sitting on the tailgate.

If you move the Unicycle ONE FOOT toward the tailgate, one foot away from the sawhorse, the weight would shift in direct INVERSE relationship to how far the unicycle has moved.

One foot is 10% of 10 feet. That means, 10% of the unicycle weight (20 pounds) is now on the tailgate and 90% of the unicycle weight (180 pounds) is on the sawhorse end.

If you move another one foot, now two feet from the sawhorse, then 20 % of the weight is on the tailgate (40 pounds) and 80% of the weight (160 pounds) is on the sawhorse.

Weight transfer, as the unicycle (load) moves across the ramp, is directly proportionate to the inverse of the percent of DISTANCE from either end of the ramp.

At no time can the weight on the tailgate, or the saw horse exceed the total weight of 200 pounds IF the ramp is supported at both ends. (One end on a sawhorse the other on the tailgate, or one end on the ground and the other on the tailgate.)
Physics says so, as will any measurement taken.


The weight can indeed exceed the total weight of the unicycle, but only if that weight is cantilever on one end of the ramp. Meaning the ramp sits on the tailgate on one end, but hangs in mid air on the other end.

Any weight place out from the tailgate with a cantilevered ramp will indeed have a load multiplier effect. I think maybe that is what you may have been thinking of.

Once again, I do not in any way wish to offend you. I just did not think it would be right to let something stand as FACT, which is in error.

Please feel free to correct me at times too. I make a lot of mistakes and try to learn from all of them. God knows I have a ½ ton to learn, especially how to load it in my Tundra!!

Have a great evening

Frank