Topic: Flex and propensity to roll

[neale_rs]

Most of the guys I wheel with are of the opinion that a Jeep with less flex is more likely to roll.

On relatively smooth off camber sections, I don't think this is true.  A Jeep with stiff springs will tilt the same as the slope while a Jeep with softer springs will tend to tilt more than the slope.

When going over a big rock one tire at a time, it seems that more flex might help... in particular, the available up-travel.  I can't see how droop could help.  Any comments on this?

[FourbangerYJ]

Most of the high zoot 3-4 link systems are set up for a metric ton of droop and fairly small uptravel. Just a few inches. The idea is to have all 4 tires on the ground as much as you can. Climbing a large rock and having the opposite tire lift off the ground is not what you want. The droop comes into play to keep the opposite tire on the ground.
Not sure on the offcamber stuff. I can kinda see what your saying but don't have a good answer if it's true or not.
I know on my leafs I have way more droop then up travel. I am real happy with my setup.

[Jeffy]

Most of the high zoot 3-4 link systems are set up for a metric ton of droop and fairly small uptravel. Just a few inches. The idea is to have all 4 tires on the ground as much as you can. Climbing a large rock and having the opposite tire lift off the ground is not what you want. The droop comes into play to keep the opposite tire on the ground.
Not sure on the offcamber stuff. I can kinda see what your saying but don't have a good answer if it's true or not.
I know on my leafs I have way more droop then up travel. I am real happy with my setup.

Those type of trucks use winches to limit travel as well.

Off-camber, a soft suspension will want to lean more.  The problem with flexing too much or leaning is that the CG shifts to to the low side.  Too much and you roll over.  Optimally, you would want it all on the high-side.

When you're three wheeling it, there is more weight on the single wheel that's planted.  So, if you have lockers, you'll have more traction.  When you flex and have a tire in a hole, there needs to be weight on that tire to have traction.  If there isn't then it's just as useless.  This is why Revolvers weren't popular (although you get a similar situation with coil suspension if the spring is too short.)

As for uptravel, I agree most have a few inches at most while the majority is all down.  I think even my SOA is about 4-6" to the bumpstop.

[neale_rs]

Thinking about it some more, it makes sense to keep the tire opposite from the climbing tire on the ground.  If it is on the ground it isn't helping to pull the body down on that side.

It looks like the ideal setup for climbing with one front tire would be a flexy suspension in front, with both compression and droop and a stiff anti- sway bar in back, so that the tire behind the climbing tire does help pull that corner of the body down.  I still think the compression is important for stability (to keep the front from rising too much, the lower the more stable and the less weight is trasferred back), although having little compression will maintain ground clearance under the rocker panels better.  The stiff sway bar in back would help make sure the body stays level with the ground where the rear axle is.  When coming off the rock with a rear tire the opposite setup would be better. But to have it work both ways would require anti-sway bars that could be turned on and off in some way.

Probably any suspension design is a tradeoff between stability, traction, and being able to maintain ground clearance.  On the high zoot suspensions, little compression and lots of droop will definitely improve traction and ground clearance.  Then they probably get stability from relatively low lift heights and call it good.

Here are some pictures of two Jeeps on the same off camber.  The flexy XJ with anti-sway bar diconnected is tilting more than the SUA YJ due to the softer springs.

[neale_rs]

When you're three wheeling it, there is more weight on the single wheel that's planted.  So, if you have lockers, you'll have more traction.  When you flex and have a tire in a hole, there needs to be weight on that tire to have traction.  If there isn't then it's just as useless.  This is why Revolvers weren't popular (although you get a similar situation with coil suspension if the spring is too short.)

This is interesting.  At some amount of droop with a leaf spring suspension the spring will begin to make the tire contact pressure less than what it would be if the tire could just hang there, the spring will start to pull up on the tire.  The same goes for a coil suspension with short springs and coil retainer clips.  Without coil retainer clips, a coil spring will never pull up on the tire.  Probably the best suspension types for maintaining contact pressure are air shocks and coilovers set up so that the springs still apply downward pressure at max droop, with coils without retainer clips coming in second place.

[sharpxmen]

This is interesting.  At some amount of droop with a leaf spring suspension the spring will begin to make the tire contact pressure less than what it would be if the tire could just hang there, the spring will start to pull up on the tire.  The same goes for a coil suspension with short springs and coil retainer clips.  Without coil retainer clips, a coil spring will never pull up on the tire.  Probably the best suspension types for maintaining contact pressure are air shocks and coilovers set up so that the springs still apply downward pressure at max droop, with coils without retainer clips coming in second place.

your shocks would also limit the travel at some point

[smashcoast]

I think the XJ in the pic above is leaning more in the front because of the coil springs. I bet the rear is the same as the YJ.

I'm looking to buy an XJ a very cheap and capable wheeler. I have heard from a lot of people that the setup of the XJ with the coils up front and leafs in the rear is an ideal setup for off roading.

[neale_rs]

I think the XJ in the pic above is leaning more in the front because of the coil springs. I bet the rear is the same as the YJ.

I'm looking to buy an XJ a very cheap and capable wheeler. I have heard from a lot of people that the setup of the XJ with the coils up front and leafs in the rear is an ideal setup for off roading.

Well, a vehicle can flex more in front than in the rear but lean is lean front and rear unless the body/frame are twisting which they do to some extent.

[jfrabat]

Theoretically, in off camber situations, more flex should result in a higher propensity to roll.  Think of a slinky...  The flex will allow more weight to be shifted to the lower side of the hill, altering the Center of Gravity, and thus increasing the chance to roll.  Anyway, I could be wrong, but it just makes sense to me.

[Mozman68]

Theoretically, in off camber situations, more flex should result in a higher propensity to roll.  Think of a slinky...  The flex will allow more weight to be shifted to the lower side of the hill, altering the Center of Gravity, and thus increasing the chance to roll.  Anyway, I could be wrong, but it just makes sense to me.

I view it as the opposite...more flex (as in flex of the axle) let's the wheel drop providing ground contact while letting the body maintain a more stable, upright position.  Less flex pulls more of the body weight towards the drooping wheel. 

Right??

[jfrabat]

I view it as the opposite...more flex (as in flex of the axle) let's the wheel drop providing ground contact while letting the body maintain a more stable, upright position.  Less flex pulls more of the body weight towards the drooping wheel. 

Right??

I'm not so sure; OK, back to basics:

I think we agree that regardless of flex, when in offcamber situations, the jeep tends to roll to the downside, right?

Also, the body wants to be centered on the two axles if level, but if tilted, it tends to roll to the downside, right?

Last, but not least, when a rig is in an offcamber situation, the weight of the vehicle is mostly supported by the lower side, as the body is leaning that way.

Now, if we agree on the 3 points above, then a flexiersetup will allow the body to roll farther to the lower side, thus affecting the CG.  If you look at the pics above, the Wrangler looks more level than the XJ.  This kind of shows what I am talking about.  Event though the axles are at about the same position, the body is leaning more.  More leaning body, more tendency to flez.  This has nothing to do with traction, it's just gravity!

[sharpxmen]

depends how the suspension is setup. The amount that the suspension is compressed on the low side should be equal (roughly) with the amount that the suspension is uncompressed on the opposite side - so the body would roll clockwise or ccw based on the side that is lowered. If the resulting center of rotation is below the center of gravity then the vehicle will be more likely to tilt and roll (the vertical from the CG will fall outside the tire contact point), if it is above the center of gravity then will be less likely to roll over (the body will tilt the opposite way which is ideal, but the CG will still move towards the side that is lower but since it is closer to the ground the effect would be less severe). Not sure if this makes sense or not. So imo all depends on how low the CG and how the suspension is setup (mounting points for the suspension arms).

in most common scenario for a lifted Jeep the CG is above the center of rotation for the body resulted from body roll.

[chardrc]

they way i look at it is like jfrabat said with the addition of considering spring constants.. comparing leafs to coils the leafs are stiffer aka higher spring constant and the coils are flexier so they have a lower spring constant their for when you go off camber the cg moves to down side so more weight goes to the low side, the leafs will move a given amount crating body roll but with the same weight the coil springs will flex more allowing the body to roll more because of the lower spring constant (how much weight (realy force but whatever) causes the spring to compress x distance. ).. vus the flexier setup is more likely to roll on off camber.. at least the way i look at it.