Outer Limits 4x4 Board

In the pic below is diagrams of a lifted coil sprung rear with

First pic, too steep a panhard angle

Second pic, angle fixed by lowering chassis mount

Third pic, angle fixed by raising axle mount




The second pic shows what I think is the best solution for stability

The third pic concerns me because the axle now articulates away from the centre line of the axle and the diff will move more from side to side under articulation as opposed to normal road use where it should just act as a normal panhard mount on the axle centre line.

Is the third method satisfactory for road use and off road use?

Does the third method increase diff travel left when the left wheel is articulated up and the right down

as well as

decrease or neutralise diff travel right when the right wheel is articulated up and the left wheel down.

The taller mount on the diff wil increase you roll centre (from memory .. I will now shut up and let the folks who know answer)

Ok no worries, I also think on second thoughts that the raised axle mount will increase sideways travel in both directions.

What is better for roll centre stability, 2nd pic or 3rd pic.


Would this be a better solution?

Some quick scrambled thoughts...Jeep drivers love changing their roll center on lifts over 2" and I have to say, they do drive bloody well compared to stock + stability when offroad appears unchanged. I think the reason they prefer to lift rather than lower is to get the panhard (or trackbar as they call it) higher and away from the ground as allows more clearance to lift tie rod/drag link higher and also in the front end it is easier to modify the steering knuckle on the axle (where the drag link attaches) and lift it higher up to maintain proper geometry with the panhard by lifting the axle end. If you drop the chassis end you also need to fit a dropped pitman arm which can weaken the steering and reduce the lifespan of the steering box.


Whatever option you pick I think its important you keep the roll center the same between the front and rear??

option three will give you less lateral movement of the diff housing as it articulates up or down. The closer to horizontal it is, the less the lateral position of the housing is affected. Also, the longer you make the panhard, the less affect it has on lateral movement of the diff housing

If you started with a horizontal panhard, as the left wheel drops downward (ie,the left end in your diagram), you will get a fairly small amount of movement to the right, as the left wheel rises, you will get the same amount of movement to the right

if you start with a steep angle on the panhard, as the left wheel drops downward, the diff will move a considerably more to the right, as the left wheel is raised, the diff housing will move slightly to the left. the steeper the angle, the more this is exagerated.

a simple line drawing on paper can highlilght this.


as for roll centre, stability etc, I have NFI

From what I understand, If you can make the pan hard run up hill ie. diff mount higher than chassie mount. On a side slope you have to roll the body uphill before it rolls down hill. But Ive never seen it done on cars only buggys.

Depending on what you want the car to do but option three is definently the go for stability the higher you can get the center of the panhard the less body roll the car will have. It works the same for all lateral control points on any suspension system, be it a panhard, a frame, triangulated 4 link etc. Effectively that point is what the body rolls around , so the more weight above that point the more weight is induced into the cars suspension as the body rolls. Obviously the flater you can get the panhard the less of a radius it will swing in stopping the diff pulling sideways as much through it's cycle.

Rhett I'd say the reason it's rarely seen in cars is because it's harder to achieve a high roll center and have the panhard uphill as the chassis and engine are in the way,
Also with higher speed stuff like outback challenge and kings, the blokes who drive and build those cars seem to think that having the panhard only pull one way is more predictable than the method you have described as the diff moves left then right through the cycle rather then just to the right.

jimmy087 wrote:Depending on what you want the car to do but option three is definently the go for stability the higher you can get the center of the panhard the less body roll the car will have. It works the same for all lateral control points on any suspension system, be it a panhard, a frame, triangulated 4 link etc. Effectively that point is what the body rolls around , so the more weight above that point the more weight is induced into the cars suspension as the body rolls. Obviously the flater you can get the panhard the less of a radius it will swing in stopping the diff pulling sideways as much through it's cycle.

Thanks that is the info I was chasing.

As someone else mentioned though it is best to have the same roll centre front and rear, what might happen if the rear was higher than the front.

Would that still be more stable than if the rear was a bit lower but the same as the front?

As fair as I'm aware having different roll centers front and rear has little affect on how the car will handle, and for that matter there are heaps of production 4wds that have different roll centers eg a car that has an ifs and leafs in the rear. It jst means that the the car might oversteer more or understeer more , probably achieve the same characteristics by changing spring rates in the front and not the rear or vicsa versa

Can you do chassis drop of pic 2 and diff raise of pic 3 same distance, panhard will be more level and be similar roll centre height to what you have ?
Could build in a few extra bolt holes in brackets to change angle for what works best for you.

On mine, I need the diff to swing a bit to be able to stop too much rubbing on chassis with 35's on full flex. It only just touches enough to take a little paint off one side.

Thanks Jimmy that makes good sense.

Doug, they are some good ideas too.

I am warming to the idea of raising the panhard at the axle with the obvious benefit of raisng the roll point, just wasn't sure what results from having the lower point of the panhard articulating further above the axle centre line than standard.

I can see that it may cause the diff/axle to act more like a pendulum under articulation and am still trying to get my head around wether or not this would be a bad thing. It may push the wheel that's under compression further outboard and create clearence issues with the guard as Doug mentions.