More articulation in rear than front?

rustyshakelford

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Please answer the question posed. Do you believe the weight on the scales goes up, down or stays the same?
Weight would stay the same

Brett
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Please answer the question posed. Do you believe the weight on the scales goes up, down or stays the same?
Yes it does, I show the case where the scale in the back went up to 75 from the original 50. But the load in the springs did not change because the control arm starts picking up load. Also notice that the only way for the scale to increase is if the scale remains horizontal. 0 friction. To do that the scale is no longer in direct line with the springs.
The guy carrying the couch up stairs carries more weight as his feet keep moving away from the couch
 

Torero

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Oh boy, you're going to make me get out my physics textbook. Pretty sure the diagrams above are not quite accurate but I haven't done the math. I'm assuming the wheels are locked (i.e., they won't either slide or roll?)
If the wheels can move at all, then it becomes a dynamics problem and that's about 2 years more of college to solve.
The original question is if the rear springs compress as the grade of the slope increases. Now bring the books.
 

Shenanigans

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Is there an engineer in the house?
 
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Maybe I haven’t encoudoes anyone here have a solid axle RC? We can quickly mode this
 
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Teghogh

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Going back to my picture. The only wheel that was on elevated ground was the front passenger and the tears were both on flat surface and yet the were flexed considerably
 
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Teghogh

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Weight would stay the same

Brett
Weigh has nothing to do with anything . It’s normal force.
If you weigh yourself on and incline you actually weigh less since the normal force is MGCosine of the angle of incline . This is why when you are braking most of the braking is done on the front since the inertia of the car pushes the weight of the car forward increasing the normal force and since the frinctionnforce if the brakes is linearly proportional to the normal force the braking increases
 

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So, if you're conceding that the weight goes up on the rear tires as the front end is raised, the next question is a general one: why do springs compress?
They compress as you put weight on them. BUT the weight has to be in the same direction the springs is facing. That’s the point of the drawing. The force still vertical but the spring is now inclined. It actually receives less weight.
 

Torero

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Sean. Regardless of the right or wrong I want to thank you for the respectful and fun discussion.
Many times here in the forum I keep from participating because lots of people have no tolerance for other’s opinion. Nice to meet you.
 

Torero

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Nice to meet you as well..and I don't mind being wrong...I'd just like an explanation b/c I'm not seeing what you're saying. It sounds like you're using a much more dynamic (and therefore, realistic) model than I am but I was being overly simplistic in an attempt to explain the concept.

Here's the thing:

I just was out in the shop and lifted the rear of my buggy (air pressure all at 5 psi) 7.5" off the ground (jack ran out of travel before I could get any higher). The front c/o springs compressed 1/4" on each side (went from 6" from the shock body to center of mounting eye on the driver side to 5 3/4" and from 5 3/4" on the passenger to 5.5"). At that pressure, the tires probably squished more than that....but the point is: the weight transferred to the front by raising the back and the springs did compress.

I was out there working on the wife's JL since we broke a bolt on her beadlock...I needed to pull the driver rear tire anyway...figured I'd repeat the procedure.

Long story short, the front springs compressed 3/8-1/2" (depending on the side) with the tires at 36 psi. I didn't measure how high the rear tires were off the ground...just went till I ran out of jack.

So far, from what I can tell, everything I stated was accurate. If it wasn't, please....please....correct me. I don't want to spread false information to anyone about anything.
In your case the floor remains the same. The point of contact of the tire with the ground changes. If you were to lift the whole garage ( like the car going up a ramp) so the points of contact of the tires remain the same, you would not see a compression on the springs.
Your example of the couch is the best to explain. Both guys walking flat hold the same weight. As one guy starts going up the stairs the bottom of the couch gets closer to the guy up and further from the guy below. If he were able to keep his feet as close to the bottom as they were when on flat, he would hold the same weight as before. ( of course he would fall backwards but that is another story) the fact that he’s feet stay several stairs away from the bottom of the couch allows him to transfer and hold more weight. Think of the axle of the car as the feet of the guy. The axle cannot move backwards and stay behind the Jeep like the guy did with his feet.
When on flat ground all the weight is on the springs and 0 on the control arms. Also there is 0 stress on the tires as to loose grip. As the slope increases the control arms start bearing some of the load and there is an increase in the force trying to make the tires lose grip. The weight of the car is still the same, it is just putting pressure on different components now. Remember your own case, what happens when you get to close to 90 degrees. If the tires are glued to the ground all the weight is going to the control arms. You have to agree that the springs are not holding weight sine they are now almost horizontal. So, when did they go from start compressing to actually extending? Never. They only extended as the slope went up transferring weight to the control arms.
 

jmcdtucson

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With a static load, and weight evenly distributed, the rear springs should compress exactly the same amount as the front springs.
Looking at my JL, the springs appear to be perpendicular to the frame. So the compressive force = Xsin(90-theta) where theta is the pitch in degrees and X is the Jeep's weight divided by 2. Compression approaches zero as theta approaches 90 degrees.
Unless there's a dynamic load, or some other difference in composition, compression should be the same.
 

jmcdtucson

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And I can imagine (I didn't check) that the rear, while being lifted, is being compressed that same 1/4" amount I noted on the front end with the rear elevated vs. the front, but there's also a lot of suspension geometry going on here as well in a more dynamic model as when you're climbing something the anti-squat, IC, and roll centers (etc.) will all come into play, especially if the axles are articulating to any significant degree.
Also weight is not centered, different angle may move the center of mass relatively forward or backward. Spring force changes as the spring is compressed. Geometry in the rear suspension probably differs from the geometry in the front. Too many variables.
 

Joe kenzo

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It’s the anti sway bar. That’s its purpose.
You don’t tear you bumper by flexing too much , you do so if you don’t have a big enough bump stop , you can have 4 inch lift and still rub if the bump stop isn’t big enough
 
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