Panhard Bar Geometry Design

[rcx132]

I'm designing the front suspension for my 4x4 buggy. It will have solid axles and long travel Fox off-road shocks. I'll post a drawing later once I get further with it. It will be a cross between a rock crawler and a trials buggy.

I've opted for three link suspension at the front which is your standard front solid axle setup, and has a panhard bar. I made this choice to avoid hydro steering which the more elaborate suspension requires.

I've set my anti-dive, minimised roll steer, optimised my ride height etc. Now just placing the panhard bar, which is something I've never done before.

So.... if I recall correctly.... the panhard bar needs to be the same length as the steering rod and at the same angle when viewed from the front?

What about the top view angle, does that also need to similarly follow the steering link?

Anything else to think about? I just watched a tutorial on YouTube, it talks about keeping the panhard horizontal at ride height, but that would be impossible on a serious 4x4.

Thanks in advance

 

[colnerov]

Hi, I always thought it had to be parallel to the ground at ride height and as long as possible to minimise sideways movement when it's swing through its arc. I wouldn't have thought with open arches that wouldn't be a problem. What about using Watts linkage or Mumford link if you want to kept it up out of the way and have parallel vertical travel (as much as possible).

 

[500e]

Here is a simple explanation of them
http://www.oocities.org/markianfox/suspension.htm

 

[Gareth_16V]

Top view geometry won't make too much difference, except perhaps if your location links cause the end of the axle (at which the Panhard rod is fixed) to move significantly fore/aft at extremes of suspension travel (which they might, as they also work through arcs).
The front view geometry is most important. Setting the Panhard rod at the same length and angle (in front view) as the steering rod will remove as much ride/roll steer as possible.

For the angle of the Panhard rod relative to horizontal at normal ride height, this just affects how much the axle is moved left-to-right through the bump and droop travels of the axle. For a 4x4 type vehicle using live axles, which isn't looking for the last 10th of a second lap time at the Nurburgring, I am not sure how much this matters.

As you know, suspension geometry is always a compromise and there are 1000 different ways to prioritise and compromise each of the details. At the end of the day, you need to arrive at a geometry that fits round everything else in the vehicle (engine, chassis, etc) and as you're building it yourself, you could have opportunity to modify or try something a bit different later on if it doesn't work exactly as hoped!

 

[rcx132]

What about using Watts linkage or Mumford link if you want to kept it up out of the way and have parallel vertical travel (as much as possible).

I looked at Watts, but it relies on a link to the chassis quite low down, so not good for a 4x4. The Mumford is interesting.

Top view geometry won't make too much difference, except perhaps if your location links cause the end of the axle (at which the Panhard rod is fixed) to move significantly fore/aft at extremes of suspension travel (which they might, as they also work through arcs).

So after sleeping on it, that's exactly what I figured out

For the angle of the Panhard rod relative to horizontal at normal ride height, this just affects how much the axle is moved left-to-right through the bump and droop travels of the axle. For a 4x4 type vehicle using live axles, which isn't looking for the last 10th of a second lap time at the Nurburgring, I am not sure how much this matters.

Yep, when I post my drawings you'll see that horizontal is just not achievable. With 15" of soft suspension and the high CofG these cars have wobbly handling anyway, so the lateral movement is fine.

As you know, suspension geometry is always a compromise and there are 1000 different ways to prioritise and compromise each of the details. At the end of the day, you need to arrive at a geometry that fits round everything else in the vehicle (engine, chassis, etc) and as you're building it yourself, you could have opportunity to modify or try something a bit different later on if it doesn't work exactly as hoped!

Exactly that. This is the third vehicle I've designed. The biggest challenges I've found is:

(a) Packaging - so getting everything to fit around everything else
(b) Compromises in the geometry, increasing one parameter forces you to decrease another and make sacrifices.

 

[PhillipM]

it talks about keeping the panhard horizontal at ride height, but that would be impossible on a serious 4x4.

The more angle the bar has the more the car will respond differently in left vs right corners, and it'll result in the body jumping up for some bumps and down for others - makes it a nightmare to tune anything else on the car. Especially if your bar is short.

 

[rcx132]

The more angle the bar has the more the car will respond differently in left vs right corners, and it'll result in the body jumping up for some bumps and down for others - makes it a nightmare to tune anything else on the car. Especially if your bar is short.

I can't quite make out what's what on that car. But it looks like a Comp Safari class car?

 

[PhillipM]

Yes, Comp car I re-worked the front geo. on for a friend to reduce his bump steer and the bar angle, as the previous setup had the bar at a fair angle and the car would lean like a bus one way in a turn and stay flat the other

 

[bricol]

Dutton a mate bought to use in classic trials had the panhard rod mounted on top of the diff, and attached to the chassis about a foot away . . handling was"interesting" - as was the tyre rub on the chassis on one side.

Now I own it, bar goes from one side of axle to opposite side of chassis - no tyre rub and it doesn't leap around.

Same car had inverse ackermann and horrendous bump steer - maybe an inch or more at the wheel rim from full droop to full bump. And self-upwinding lock - to avoid the tyres hitting the body, there was bracket welded to the front lower wishbones to hit the bolt securing the steering link arm to the upright - so if you had full lock on, holding it against this stop, as the suspension either drooped or bumped, it forced the lock off . . .

None of that happens now

 

[rcx132]

Dutton a mate bought to use in classic trials had the panhard rod mounted on top of the diff, and attached to the chassis about a foot away . . handling was"interesting" - as was the tyre rub on the chassis on one side.

Now I own it, bar goes from one side of axle to opposite side of chassis - no tyre rub and it doesn't leap around.

Same car had inverse ackermann and horrendous bump steer - maybe an inch or more at the wheel rim from full droop to full bump. And self-upwinding lock - to avoid the tyres hitting the body, there was bracket welded to the front lower wishbones to hit the bolt securing the steering link arm to the upright - so if you had full lock on, holding it against this stop, as the suspension either drooped or bumped, it forced the lock off . . .

None of that happens now

So basically it was built with no consideration of the geometry? As are so many builds I've seen.

 

[Morrisman]

So what is “basic three link”? How do you set anti dive with it?

I’ve used triangulated four link on a couple of rear ends, which works well, no binding, no 5th link Panhard rod required.

It would also work on a front axle. I guess. This is a google picture but mine were similar setup.

 

[Gritineye]

Philip, I built a few off road comp cars years ago, I used panhard rods as you've described, parallel to and same length as steering rod. they weren't too far off parallel to the ground at rest.

I used 3 link axle location, the bottom ones where tube about 1 1/2", the top link was offset quite a lot to miss the engine they were solid and only about 3/4" dam as there's very little load on them, can't remember how long prob about 3ft.

Never had a bar break and no bump steer even flat out, they were quite successful in their day but I suspect you'll be looking for super extreme travel nowadays .

Heres a pic of one of my cars.

edit

Here's a pic of one when new, bar at more of an angle to the ground than I remembered them.

 

[rcx132]

So what is “basic three link”? How do you set anti dive with it?

I’ve used triangulated four link on a couple of rear ends, which works well, no binding, no 5th link Panhard rod required.

It would also work on a front axle. I guess. This is a google picture but mine were similar setup.

View attachment 173763

This is 3-link. None of the links are triangulated so the panhard bar restricts lateral movement and keeps it in line with the steering rod.

The pic you showed requires hydraulic steering as the axle moves relative to where the steering box would be, so steering would be all over the place.

 

[Morrisman]

This is 3-link. None of the links are triangulated so the panhard bar restricts lateral movement and keeps it in line with the steering rod.

The pic you showed requires hydraulic steering as the axle moves relative to where the steering box would be, so steering would be all over the place.

No, the single top bar of your 3 link is replaced with the triangulated two bars, which means no Panhard rod required. The Panhard gives more lateral movement than the triangulated setup, due to the fact it describes an arc as the suspension travels.

There are various ways to set up the triamgulated four bar, but generally the ‘triangle’ locates the top of the diff dead central, which affects roll centre positively, apparently....

The links can be located either side of the diff, on the axle tubes, so the centreline of the axle is more centrally affixed, depends what works best with your steering linkage.