How does a mid-arm suspension improve the climbing capabilities from the drivers seat?

[mattcogdell]

I've noticed just recently looking at other members wheeling photos and taking my own photos/video while out on the trail, how when climbing with short arms the rear end walking under the jeep. In these photos you'll notice one jeep with mid arms. During the travel of the suspension the axle stays centered in the wheel well. The other two jeeps, during a climb the axle walks under the jeep. I had a conversation recently with a gentleman with the mid arm and he stated this before I understood what he meant by it.

My question is how does the mid arm improve the climbing capabilities from the drivers seat? I am very curious how different the jeep reacts to the climb. Does it build confidence in climbing larger or harder obstacles you were hesitant to try before? Does it also improve traction?

 

[jjvw]

When it matters, I thought it would be the front walk that is more troublesome than the rear.

A "longer arm" that also has good geometry is going to climb with more calmness than a similarly lifted short arm. It will also put more weight on the front end during a climb than a typical long arm kit because the rear doesn't sink under load. All of that translates into improved traction and stability.

Something I have noticed on mine with the Savvy kit and honestly don't understand yet is that mine doesn't lift wheels as often or to the same extent as other similarly built short and long arm TJs.

@strumble8, remind me to try the LJ line next year.

 

[Southtowns27]

Something I have noticed on mine with the Savvy kit and honestly don't understand yet is that mine doesn't lift wheels as often or to the same extent as other similarly built short and long arm TJs.

Do some research on suspension "anti-squat", it'll all make sense

 

[jjvw]

Do some research on suspension "anti-squat", it'll all make sense

I'm familiar. That isn't what I'm noticing. At least not in the way I understand AS and IC.

 

[Bigmac]

something blaine showed me explaining it (after i showed total ineptitude) : put a wooden board on an incline, put a water bottle on the board, push the water bottle up the board with the end of a pencil.

notice that the length of the pencil does not influence your success, its how high or low you place the pencil on the bottle.

the mid arm length is not what makes it successful in it's climbing ability, it is the location of the mounts on the frame.

some other forces at work here as well, but like i said. I am mostly inept at the geometry of it.

 

[Bigmac]

My question is how does the mid arm improve the climbing capabilities from the drivers seat? I am very curious how different the jeep reacts to the climb. Does it build confidence in climbing larger or harder obstacles you were hesitant to try before? Does it also improve traction?

To answer the original question (in my opinion) the Jeep feels leaps and bounds more controlled and stable in a climb. I've been in similar situations before and after the mid-arm (like lifting a front tire mid steep climb) and the feeling is drastically different. like comparing knee shaking adrenaline to a calm "hmm let me back up and try another line"

even my wife (who sometimes panics) just let me walk right up the wrong line and get on 3 wheels. she commented on how much more stable the jeep "looked" than it did before the mid arm.

I had a spotter on hells gate who got me in a pretty bad place, I was up on 3 with the front right tire way up. I could have run the winch, but felt safe backing down several feet, and continuing on my own chosen line. something i would never have even attempted with my previous short arm.

can't say much for the traction aspect. Its all sandpaper.

this got worse before it got better.

 

[JMT]

To answer the original question (in my opinion) the Jeep feels leaps and bounds more controlled and stable in a climb. I've been in similar situations before and after the mid-arm (like lifting a front tire mid steep climb) and the feeling is drastically different. like comparing knee shaking adrenaline to a calm "hmm let me back up and try another line"

even my wife (who sometimes panics) just let me walk right up the wrong line and get on 3 wheels. she commented on how much more stable the jeep "looked" than it did before the mid arm.

I had a spotter on hells gate who got me in a pretty bad place, I was up on 3 with the front right tire way up. I could have run the winch, but felt safe backing down several feet, and continuing on my own chosen line. something i would never have even attempted with my previous short arm.

can't say much for the traction aspect. Its all sandpaper.

View attachment 124705
this got worse before it got better.

Your rear passenger looks way too far passenger. I must have had a good spotter. I wondered afterward how anyone could mess that obstacle up. Now I can see. Looks like it got hairy pretty quick. Interesting discussion on mid- vs short arm

 

[Brianj5600]

The believe biggest problem with lifted SA suspension is that the stock mounts aim the lower control arm at about the same angle as the AS line. I moved the axle UCA up about 3" thinking that would help lower AS, but seemed to have little to no affect. I later played around with Triaged and confirmed that the lower arm angle has more to do with AS. I drilled pilot holes for Nth degree LCA relocation, but not sure if the rear leaves enough room for the joints. Lowering the LCA angle will help with excessive AS and lower the IC. It seems like there is little conversation on IC length and height and how they change characteristics.

 

[Bigmac]

Your rear passenger looks way too far passenger. I must have had a good spotter. I wondered afterward how anyone could mess that obstacle up. Now I can see. Looks like it got hairy pretty quick. Interesting discussion on mid- vs short arm

my first and only time there. total stranger offered to spot me, claimed to be an expert who had spotted tons of people up it. once the wall was in my window i hollered up to him "ok so what now" i hear him say " uhhhh.... you might have to back up" at that point i knew that the magnetic pull i had toward a different line the whole way up was my gut trying to save me from following bad advice.

after i backed up the wall fell away from the window a couple feet. my "spotter" wasn't really sure what to try next. i suggested i steer left up the wall and that it would force the right side down. He wasn't sure, but i was done listening at that point.

 

[JMT]

my first and only time there. total stranger offered to spot me, claimed to be an expert who had spotted tons of people up it. once the wall was in my window i hollered up to him "ok so what now" i hear him say " uhhhh.... you might have to back up" at that point i knew that the magnetic pull i had toward a different line the whole way up was my gut trying to save me from following bad advice.

after i backed up the wall fell away from the window a couple feet. my "spotter" wasn't really sure what to try next. i suggested i steer left up the wall and that it would force the right side down. He wasn't sure, but i was done listening at that point.

My gut is always to keep the Jeep level. The guy who spotted me was 70+ years old and he ran the escalator in 3 minutes in a TJR with 2” lift, 2” TT, manual and 32’s. He knew exactly what he was doing. He probably spotted 20 rigs up Hell’s Gate while I watched. Some were pickup trucks that looked wrong being there.

 

[astjp2]

The believe biggest problem with lifted SA suspension is that the stock mounts aim the lower control arm at about the same angle as the AS line. I moved the axle UCA up about 3" thinking that would help lower AS, but seemed to have little to no affect. I later played around with Triaged and confirmed that the lower arm angle has more to do with AS. I drilled pilot holes for Nth degree LCA relocation, but not sure if the rear leaves enough room for the joints. Lowering the LCA angle will help with excessive AS and lower the IC. It seems like there is little conversation on IC length and height and how they change characteristics.

The Nth drill jig leaves enough. Barely

 

[kmas0n]

I'll take a stab at this...
Ok, anti-squat is what happens when torque is applied to a link arm setup. it literally reduces the amount of squat in the rear end under acceleration. A factory TJ has around 100% AS (anti-squat), so, not much happens when you accelerate. A TJ lifted 4" with factory control arms has closer to 200% AS, which means that the rear axle is attempting to rise up and get up under the frame under acceleration (at nearly twice the force as a non lifted jeep). It applies force to the lower control arm mount and tries to lift the jeep up from that point. The vehicle's entire weight shifts rearward from acceleration, and gravity wins overpowering that lifting force. But It still has upward force that is realized by taking some of the weight off the front suspension. That is why despite having a lot of AS, you don't feel the rear end rise up, you feel the front rise up instead. When you get into very steep climbs and your traction is adequate, all that upward force starts to add up... ALL of the torque goes into attempting to lift the jeep by its rear lower frame control arm mounts. The steeper this angle, the more it's felt, the more AS built into the suspension, the more it is felt. the force is being applied at the angle of the control arm so draw an imaginary line at the angle of the control arm. Is that force aimed at the front bumper, or at the top of the windshield? If its the top of the windshield it is getting close to the center of gravity (front to back). Look at the red jeep and follow the angle of the rear control arm, its getting near vertical. There is no weight left on the front axle and you can see the driver's side tire is barely touching despite barely any droop.

Now imagine moving the frame side control arm mount forward, that line starts to move from vertical to horizontal the further out it goes. As the imaginary line moves forward so does the weight on the front axle.

The reason JJVV doesn't lift a wheel is the savvy mid-arm has low AS, remember back to the 100% vs 200%. Nothing in that lift is by accident and few compromises were made. so that force is reduced. It's more than just lower control arm angle. Long(er) arms alone are not the cure.

**edited like 5 times for clarity**

 

[kmas0n]

Here's a test for you. measure the height of your front bumper from the ground. place jack stands under the frame side rear lower control arm mounts, the same height as ride height. Now lift the rear of your jeep by the pumpkin. remove tires and lower the pumpkin so the axle hangs free. Now remeasure the front bumper. it will be 2-4 taller. The jack stands change where the force is applied and take some weight off the front end.

 

[jjvw]

Piecing together some of what @Bigmac and @kmas0n have written and how I barely understand these things, can we say that flattening the lower rear arm makes the rear axle push the Jeep forward at a lower point, similar to pushing the water bottle from it's base rather than it's top?

I'm not sure where that translates into keeping the wheels on the ground and the appearent ability of the suspension to better conform to the terrain that isn't necessarily a climb.

 

[kmas0n]

I'm not sure where that translates into keeping the wheels on the ground and the apparent ability of the suspension to better conform to the terrain that isn't necessarily a climb.

I can't explain this one, because I don't understand it either. But it is there, the difference is obvious when you drive a Jeep with factory control arms and then a jeep with mid arms back to back with all else being equal (antirock, lift height, tire size, etc). A friend best described it as "it just transitions over uneven terrain so much smoother." I lack the verbal skills to articulate it any better.

 

[jjvw]

I can't explain this one, because I don't understand it either. But it is there, the difference is obvious when you drive a Jeep with factory control arms and then a jeep with mid arms back to back with all else being equal (antirock, lift height, tire size, etc). A friend best described it as "it just transitions over uneven terrain so much smoother." I lack the verbal skills to articulate it any better.

The best I can come up with is this characteristic is more closely related to the 3/4 link having less inherent bind in the system. Compared to others I have worked on, without springs and shocks, my axles are completely free to move when cycling with a floor jack. Though, the significance of that freedom of movement is diminished when there is 4,000lbs acting on the suspension.

 

[mrblaine]

something blaine showed me explaining it (after i showed total ineptitude) : put a wooden board on an incline, put a water bottle on the board, push the water bottle up the board with the end of a pencil.

notice that the length of the pencil does not influence your success, its how high or low you place the pencil on the bottle.

the mid arm length is not what makes it successful in it's climbing ability, it is the location of the mounts on the frame.

some other forces at work here as well, but like i said. I am mostly inept at the geometry of it.

Basically what you are trying to do is focus the line of force through the center of gravity to move the rig up an incline without pushing the front down too far or lifting the front too far. If you push the front down too much, the rear suspension lifts the back of the rig, the axle tries to crawl under it until it breaks traction and repeats the cycle quickly with what is demonstrated as hopping. If you push the back of the rig down while climbing, the front lifts until bad things happen. You want just enough past neutral to keep the nose down without raising the rear which will generate the most traction.

 

[mrblaine]

It seems like there is little conversation on IC length and height and how they change characteristics.

I won't and don't get involved in those conversations due to one basic fact. The 4 link calculators are just a starting point to stick some shit on the rig and then go test it to see how it all works dynamically because they are a static calculator. Once the weight shifts and the CoG moves, the calculator goes out the window and now you're just seeing what works. That and no one ever actually calculates the CoG, they best guestimate it and base all the measurements and locations off of flawed input. My preference is to work within the constraints of the chassis and body, build something based what can be fit, go test it and change it until it works, change it some more until it quits working, and then change it back some. That has worked very well.

 

[astjp2]

I won't and don't get involved in those conversations due to one basic fact. The 4 link calculators are just a starting point to stick some shit on the rig and then go test it to see how it all works dynamically because they are a static calculator. Once the weight shifts and the CoG moves, the calculator goes out the window and now you're just seeing what works. That and no one ever actually calculates the CoG, they best guestimate it and base all the measurements and locations off of flawed input. My preference is to work within the constraints of the chassis and body, build something based what can be fit, go test it and change it until it works, change it some more until it quits working, and then change it back some. That has worked very well.

I have the scales and have yet to do a COG calculation. It will vary as your vehicle moves up and down and your suspension moves, but here is a good explanation of it to add to what Blaine says.

http://www.thecartech.com/subjects/auto_eng/Center_of_Gravity.htm

 

[kmas0n]

4 link calculators are just a starting point to stick some shit on the rig and then go test it to see how it all works dynamically

Agree 100%. This is all they are good for, and they are good for this.