Suspension

[robhybrid]

I am under the impression that lifting the panhard rod at the axle could possibly improve off road stability but I am keen to be proven otherwise?

[plasticbadger]

Lifting the panhard rod relative to the axle will raise the roll centre (the point around which the body rolls compared to the axles) In theory, the closer the roll centre is to the centre of gravity, the less the body will roll as the lever arm of the body weight is reduced. In practice though I would think that by raising the roll centre, as in right hand pick, you will increase the lever acting on the springs during roll and would need a stiffer spring to reduce roll.

My preferance would be to keep the panhard parallel to the ground at ride height and low down on the axle, then work on lowering the centre of gravity in the body. Also work on controlling roll with spring rates and positioning.

Roll steer will be reduced by a long, parallel to the ground panhard rod and long suspension links.

For further reading try the book Chassis Engineering by Herb Adams, also try looking at Pirate forum, as if you put your suspension design into the 4 link calculator then plenty of people will tell you what's wrong with it!

[Daan]

Lifting the panhard rod relative to the axle will raise the roll centre (the point around which the body rolls compared to the axles) In theory, the closer the roll centre is to the centre of gravity, the less the body will roll as the lever arm of the body weight is reduced. In practice though I would think that by raising the roll centre, as in right hand pick, you will increase the lever acting on the springs during roll and would need a stiffer spring to reduce roll.

It is the other way round, you decrease the lever for the cofg to work on and therefore the roll will reduce, like I mentioned in my previous post.

[elbekko]

http://www.pirate4x4.com/forum/showthread.php?t=204893

There's both a 3-link and 4-link calculator there. The 3-link one should do panhards.

[ToyRoverlander]

http://www.pirate4x4.com/forum/showthread.php?t=204893

There's both a 3-link and 4-link calculator there. The 3-link one should do panhards.

Also, keeping the rollcentre of the front suspension lower than the rears increases roll stiffness as the 2 points are not in the same plane horizontally. Helps with handling onroad.

[robhybrid]

Also, keeping the rollcentre of the front suspension lower than the rears increases roll stiffness as the 2 points are not in the same plane horizontally. Helps with handling onroad.

Hadn't thought of that but it makes sense.

There are a few good ideas coming through here.

[Bush65]

Roll axis is different to roll centre. There is a suspension roll axis (i.e. for front and rear suspension) and another axis for the vehicle - the axii that the front and rear axles and the body pivot about.<div><br></div><div>The roll centres (one for front and another for rear axle) are the points that the front and rear roll axii intersect the vertical plane through the centreline of the particular axle.</div><div><br></div><div>To visualise roll axis you need to view the suspension from the side, not front or rear of vehicle.</div><div><br></div><div>You find the suspension roll axii by finding 2 points that are <i>fixed</i> when the axle assembly articulates. The line that joins these 2 <i>fixed</i> points is along the roll axis. Note: fixed does not mean forever <i>fixed</i>, just <i>fixed</i> for an instant while the axle is rotating.</div><div><br></div><div>Take some examples of the location of these fixed points on various suspension components:</div><div><br></div><div>a) A-frame: the pivot point of the ball joint at the apex of the A-frame. It should be clearly seen that this point can't move during the instant while the suspension is articulating. It can move while the suspension is rising or dropping, but that is not what we are discussing - in that case the roll axis has to be re-calculated.</div><div><br></div><div>b) Watts link: the pivot point of the centre (vertical) link on the axle housing.</div><div><br></div><div>c) Panhard rod: the point on the panhard rod where the rod intersects the vertical plane through the centerline of the vehicle.</div><div><br></div><div>d) 2 triangulated links: project the axii of both links to the point where the intersect. The point can be close to the ends of the links if the angle between them is great, or the ends are close together (resembling an A-frame).</div><div><br></div><div>e) 2 parallel links (like Land Rover rear trailing arms): as for example d) above - just remember that parallel links intersect at infinity (a long way away!).</div><div><br></div><div>Now look at the slope of roll axis and how it affects roll steer - remember we visualise this slope looking from the side of the vehicle.</div><div><br></div><div>Take the stock rear suspension of a coil sprung Land Rover:</div><div><br></div><div>As per a) above, we find one point on the roll axis at the centre of the ball joint at the apex of the A-frame. The second point is where the trailing arms intersect - a long way in front of the vehicle.</div><div><br></div><div>Now draw a line that represents the roll axis (in your mind or on paper) through those 2 points (looking from the side) - it will go from the ball joint and will be parallel to the trailing arms.</div><div><br></div><div>With stock suspension the roll axis slopes up toward the front. When the axle articulates it is pivoting about this axis and the upward slope of the roll axis forces the wheel on one side to move forward while it droops and the opposite wheel to move back while it moves up. One wheel moving forward and the opposite moving back is what causes that axle to steer to one side (roll steer).</div><div><br></div><div>Now raise the suspension and see that the slope of the trailing arms increases. Thus the slope of the roll axis also increases, worsening roll steer.</div><div><br></div><div>There have been suggestions for improving roll steer, e.g. longer trailing arms. Most likely (depending where the chassis end of the arms are located) this will lower the slope of the arms, hence the roll axis.</div><div><br></div><div>Take the proposed inverted A-frame with panhard rod (or Watts link) per the original post.</div><div><br></div><div>We have one fixed point on the panhard rod (or Watts link). A second fixed point is at the joint at the apex of the inverted A-frame where it is connected to the chassis.</div><div><br></div><div>The roll axis passes through both of those points. The roll axis will be flat if the heights of both points is identical, otherwise it will be inclined and cause roll steer to a greater or lesser extent, depending on the slope (difference in heights).</div>

[Bush65]

Something very weird is going on with my previous post. When originally posted, all of the blank lines to separate the post into paragraphs to make it easier to read were removed.

When I tried to edit it, to make paragraphs, not only were they removed again, but the italic formatting together with line breaks were removed and now replaced with tags. So I have given up.

[robhybrid]

I cut and paste the post above into word just so I could split it into paragraphs before reading one bit at a time.

Why couldn't you live in W rather than NSW

So as far as roll steer is concerned the right hand side picture from my previous post has got plus points albeit with a drop arm on the chassis end similar to the left hand picture (to flatten panhard rod angle)

As I will need to fabricate all my suspension mountings I cant see it being a problem to make a raised axle panhard rod mount (possibly at the expense of a little bit of panhard rod length)?

more like this?

as for the joint for the A frame I was thinking of using lr hockey stick style mounts at axle thus giving a little rubber bushing and at the chassis end making myself something like this :-

I have got thoughts of cutting up 2 50mm trailer hitches and welding plates to them so I can bolt 2 half's together to get something very similar, Yes I can use a welder, yes I can appreciate the safety implications.

does anybody know where I could purchase a joint like this cheaply otherwise?

[elbekko]

I'm thinking something Uniball like perhaps, I'd trust that much, much more than a trailer hitch to be honest.

http://www.polyperformance.com/shop/Uniballs-p-202.html

"# Features 32 Degrees Of Misalignment With Spacers"

That doesn't sound too shabby I'd say, not sure if you could get more with the setup from your picture and still maintain the required strength.

[robhybrid]

If not - I have a cunning plan! I have another type of joint in mind which should be pretty good in that application.

Si

give us a clue?

[simonr]

give us a clue?

After I've finished milling this TDS winch multi motor thingy - I'll make one and post piccies! Don't want to describe it in case someone else jumps in and beats me too it!

Si

[Soren Frimodt]

Well.. Using a trailer hitch does sound a bit spooky, but when you think about it, this thing can really handle some loads! Over on PBB there is a guy who made a huge buggy thingy with just this setup, see it here: http://pirate4x4.com/forum/showthread.php?t=899253

Also the reverse A-arm setup is widely used here in Denmark. And is really simple, reliable and dirt cheap to make. For several years members of the Danish Toyota 4WD Club has been using this setup on there racers, and they never seem to fail (if build properly of course). So I wouldn't hesitate to go that route.

Although I like the double triangulated four link and it's un-doubtable strength and predictability, it is somewhat a hassle to make.

[simonr]

A trailer hitch was the inspiration for the original X-Joint. I realised though that with the kind of mud we have here, a simple hitch would not last long.

Also, in tests, it only took 2 ton of force to pop the ball out of the hitch. The test was done on a grown-up 3.5 ton rated hitch. The longitudinal force that a trailing arm on a Lands Rover sees is about 2.2 Ton peak - so using a hitch was a non starter.

The joint in an inverted A Frame will see about 10 ton compressive & tensile loading and about the same in shear, particularly if you land on the A frame - so the joint needs to be fairly beefy, particularly if you include a 6 x safety margin! You also have high cyclic loads which lead to fatigue. All in it makes the design of a suitable joint almost impossible!

With an X-Joint or trailer hitch, the most likely failure is for the ball to snap off the A frame - which leaves you minus an axle (not good!) My conclusion is that the best option for a joint is one in which no single point failure results in the axle falling off even if that places some limitations on the rest of the design / operation. At the very least it should have a 'safety chain' or similar

Si

[Anderzander]

Get over it. Don't invent excuses for badly balanced suspension - learn to read the situation better.

Go for balanced articulation that can be easily driven over obstacles that are more difficult than you could tackle with your poorly balanced suspension.

Got to agree with that.

A tighter front end will force the back to articulate hugely before you get movement in the front. So if you are driving up hill the back will articulate taking weight off one of the drive wheels, which is the opposite of what you want.

A lot of Land Rovers are modified like this - with huge rear, non binding, articulation and much less, binding, articulation on the front. They'd actually do better in the example I gave, driving backwards.

Balanced suspension helps keeps the weight balanced over the wheelbase - which gives a much better chance of achieving drive and traction. Its amazing how far you can go without cross axle diff locks if you have balanced long travel suspension - which is I believe the original Range Rover philosophy.

[elbekko]

As Si said, trailer hitches weren't made to withstand that sort of forces. They're made to be able to pull a few tonnes of trailer (on wheels!) along. If you'd try to stop a fully laden 3.5T trailer without trailer brakes, I'm not too sure how long that hitch would stay unexploded.

[ToyRoverlander]

Got to agree with that.

A tighter front end will force the back to articulate hugely before you get movement in the front. So if you are driving up hill the back will articulate taking weight off one of the drive wheels, which is the opposite of what you want.

A lot of Land Rovers are modified like this - with huge rear, non binding, articulation and much less, binding, articulation on the front. They'd actually do better in the example I gave, driving backwards.

Balanced suspension helps keeps the weight balanced over the wheelbase - which gives a much better chance of achieving drive and traction. Its amazing how far you can go without cross axle diff locks if you have balanced long travel suspension - which is I believe the original Range Rover philosophy.

I agree!!

[will_warne]

Some very good stuff here! One thing to think about Rob is coil overs allow you to have your cake and eat it: soft initial travel, firmer when the main dual rate slider hits the stops and nice and firm when the bump stops start working. I have also designed an anti roll system that shouldn't limit axle articulation. It isn't perfect - it won't work in the example you give when only one wheel is pointing down hill but it will make a huge differance on side slopes and higher speed cornering. Watch this space!

[rachely476]

http://www.pirate4x4.com/forum/showthread.php?t=204893

There's both a 3-link and 4-link calculator there. The 3-link one should do panhards.

Thanks for sharing the link!

[ToyRoverlander]

I have also designed an anti roll system that shouldn't limit axle articulation. It isn't perfect - it won't work in the example you give when only one wheel is pointing down hill but it will make a huge differance on side slopes and higher speed cornering. Watch this space!

There are already many of those available. Here's one for instance:

http://www.m-a-engineering.net/Sway-Bar-Kit-SXY.htm

PolyPeformance has a few to choose from as well.

[simonr]

I think Will is talking about something which allows articulation on opposite directions on the two axles, but resists both leaning in the same direction - stopping it leaning on side slopes but allowing cross-axle.

It could be achieved by connecting a prop shaft to the axle casing such that the prop turns as the axle articulates then joining both props in the middle with a differential. Lock the pinion and it will only allow articulation.

The trouble is, the same as I experienced with my buggy, that diagonal side slopes are if anything more common than regular side slopes on challenge events (and presumably trials). I thus contend that the vehicle needs to be ballanced in it's resistance to side slopes and articulation for good performance in real world situations. Too much freedom of movement is just as limiting as too little.

About the only thing that I think has mileage is forced articulation - using hydraulics (or similar) to limit articulation in some circumstances and force it in others, or more accurately to force the limitation of articulation so when you get in to a situation where it is a problem, you can undo it.

Si

[robhybrid]

Some very good stuff here! One thing to think about Rob is coil overs allow you to have your cake and eat it: soft initial travel, firmer when the main dual rate slider hits the stops and nice and firm when the bump stops start working. I have also designed an anti roll system that shouldn't limit axle articulation. It isn't perfect - it won't work in the example you give when only one wheel is pointing down hill but it will make a huge differance on side slopes and higher speed cornering. Watch this space!

For now as funds are a limiting factor I have thoughts on using landrover springs Possibly lightest available v8 front?

and Gwyn Lewis challenge rear spring relocators with his peperpot spring retainers,

I am not sure about shocks but I do already have ome +5.5" shocks and had thoughts of mounting them at a steeper angle in towards the center of the chassis?(anybody remember the gone to far rear suspension setup?)

I might add a anti roll bar if I feel the need.

This is for a trials/winch challenge buggy not road use.....

Has anyone ever put a anti roll bar, front to rear axle? I could see it possibly helping with climbs and descents?

Si's shafts to a diff with locked pinion sounds interesting but space and weight? I have got a dead 4x4 quad bike front axle in amongst my scrap selection though. Would it force the front to travel equal to the rear? cab constantly mid point regardless? would the diff mounting have to be pretty substantial? quad bike diff strong enough?

[elbekko]

Has anyone ever put a anti roll bar, front to rear axle? I could see it possibly helping with climbs and descents?

Something like a chassis, then?

[robhybrid]

Something like a chassis, then?

not quite I'll see if I can draw a picture

[Bowie69]

You mean like an anti-dive/squat bar? In other words an anti-roll bar following along each chassis rail, then taking a turn and connecting to the outer edge of the axle, thereby inhibiting flex?