Why are panhard rods always on that side?

Thanks 4t64rd. You make me look good

Pete

 

Here is a pic of the Rear suspension I built with a Wob Link.

It's a De Dion, built as a spaceframe that wraps around the Engine and Gearbox.
The rear wheels were adjustable for Toe in/out and Camber.
You can see that I reversed the Wob link so the pivot point was on the axle.
I thought that was better because I could get the R/C lower that way ( I didn't know any better...)
It still worked really well, but because the car was really short and wide it was a handfull.

 

Whaddayaneedusfor?

seems to me you guys have done a fine job of enlighteneing each other without any input from me. Some really worthwhile stufff here.

 

Funny, I asked Keith Roland (local semi retired, in his late 80's sprint and Indi car builder, he did the chassis on the Orange Crate when he worked for Tindle in the early 60's) about this when he had his track T for sale. He pointed out a few things that made sense (on a sprint car he was working on at the time, no less). 1. The side shift of the axle is minuscule if the panhard rod is as long as possible and mounted level with the chassis set at ride height (something around 1/16" if my memory hasn't failed). 2. Mounting points should be on the chassis on the same side front and rear to minimize upset as the suspension works. 3. The chassis mounting points should be on the same side as the steering box if cross steering is used (not a consideration on a sprint car with cowl steering). 4. Although a watts link has no side shift (unless you're using one with asymmetrical links to clear the pumpkin and the suspension travel extends the bellcrank overcenter), the benefits are neglible and not worth the complexity and added weight.

 

OK...I'm freaked out by the thought that went into that!
I've always visualized a DeDion axle as a single tube without easily tunable wheel alignment settings.

A smart MODIFIED builder could use ideas from that setup to build a very cool Hot Rod with some CHEAP latemodel parts, while keeping the RACE look a Mod needs...
(Wouldn't need to be rear engine either to use the visual impact of a DeDion multitube or monotube axle.)

I can see how it works...but would NEVER have dreamed it up.
That was a clever bit of engineering Alex!

 

Buggered if I can see it....

 

Thanks Bill.

I saved your pic because it shows exactly what's what...

Here are some more pics.

In them you can see more of the De Dion.
It was a completely seperate Spaceframe, built out of steel tubing with aluminum riveted and glue'd to it ( the chassis was a modified Lola Monocoque ).

I also stuck in a side view pic to show how short it was, and a pic of it cornering...

 

WOW! That car is the TOY I wanted for Christmas when I was 12 or 13!
I STILL want it!!!!

Looks like it should have a plastic T handle for a kid to pull on to make it go down the sidewalk!!!

A LOLA chassis. There's history for ya...
I'd love to have the ability to really wring that out! Even just to take it out and spin out in every turn would be fine with me!!! Hahaha

Man! You've built some interesting stuff...and all badass too.

 

I feel like I read through this post and the responses pretty carefully.

One thing I didn't see - as far as front panhards go on side steer cars - was the cumulative effects of mounting the frame bracket on the passenger side of US and other left steer cars.

Just to make the math simple, let's suppose the panhard arc travel measures 1/8" from one extreme of travel to the other.

Let's suppose as well the drag link arc travel measures 1/8".

Since a panhard of correct length is very close to the length of the draglink it's easy to see the cumulative effects of arc travel for both are self-cancelling.
In other words there is no steering input from a difference in arc lengths between drag link and panhard.

There will be a small steering input due to travel from the drag link, but it will be no more than the 1/8" mentioned.

With a left steer car and the panhard bracket mounted on the (US) passenger side the effects of arc travel are cumulative and you now have 1/4" of input since the drag link is pushing the steering arm one way and the panhard is pushing the axle the other way.

Since these solid axle cars don't have the suspension travel the jeeps do and in fact the panhard/drag link combo doesn't swing too far the actual horizontal travel due to arc offset is minimal.
Perhaps 1/16" at the most.
(Easily figured with tape measure, square, pencil, piece of string and a clean garage floor.)

Since the travel is fairly limited, this is why the right/left mounting scenario of side steer box and panhard bracket mount works for some.

Even so, just because it works doesn't mean it's right.


As far as the rear panhard goes, mounting the bracket on the opposite side of the steering box strikes me as not being correct either.
Commercially built Jeeps or not.
Jeeps are designed to do several things fairly well, but any one thing is not done completely well.
There's always compromises and since we're not building Jeeps here nor going off-road we should concentrate strictly on the street-handling side of the question.

Most times the rear panhard is overly short, but even then the arc travel isn't too large.
Even so, the deflection from a full squat of the rear suspension can set the car off at an angle at the rear which in effect cant's the front wheels at an angle to the direction of travel.
Since arc travel isn't much, the chassis doesn't affect the steering equation too strongly, but it does affect things.

Most of us have gone over a road where the drop down to the next level (otherwise known as a dip) dang near bottoms the car out after we've had a short flight at less than one G or in some cases entered the negative G region.
When the car bottoms out, the panhards input a steering component at both ends and if the panhard mounts at both ends are on the same side, no big deal.
If they're mounted opposite then you have the cumulative effects of arc travel.

A lot of this can be alleviated by by mounting the panhards as close to horizontal as possible.

In any event, chalk me up as one who mounts the panhard brackets - front and rear - on the same side as the steering box.

Interesting . . . and educational discussion so far.

 

Thanks for the great input from everyone involved, now it's my turn for a question. Considering the above info regarding the front travel with opposing arcs, the arcs are easily visualized if vertical wheel travel is equal on both sides.
As most of the rods were are discussing are buggysprung with the pivot being the center of the spring and the shackles, would a situation such as hitting a pothole or rut where the vertical wheel travel was in opposing directions be more inclined to induce bumpsteer with the panhard mounted on the passenger side of a cross steer setup?

CC

 

I would think so.
You're still swinging an arc with the drag link and panhard.

As I alluded to above, these arcs - if the panhard is sufficiently long - don't really input much horizontal travel and if the drag link and panhard are parallel with one another etc. the bumpsteer effect is very minimal with the steering box and frame bracket on the same side.
Which is to say, bumpsteer is effectively non-existent.


Without firing up the radial vs bias ply debate, the radial equipped car would be more forgiving in the bump steer regime due to the flexier sidewalls.
Even so, if you slipped bias plies on the same car you removed the radials from I don't think you'd notice a bump-steer problem.

All I can really pass along is personal experience and to that end, my 32 with Vega cross-steer, long panhards front and rear, radials both ends handles well, is a pleasure to drive and I've never noticed any bump steer.

Not necessarily a part of this discussion, but a great deal of the 32's good handling manners is due to the rear sway bar.
Makes all the difference in the world.
And aside from what some folks experience in the sporty car world a sway bar is not needed on both ends.
You don't need a killer, large OD sway bar, they'll work ok, but general driving at low speeds and in-town corners is a pain the backside.
I like the Deuce Factory sway bars and have one on both cars.
Nice part is, they're about the most compact sway bar setup out there.

A little searching in the junkyard and you should be able to find an adaptable sway bar off an econo-box sized car that would work fine on a thin-fender.
Don't overlook the foreign cars either.
I would not hesitate to use a piece off a Toyota if that would get the job done.
(In fact, I run a Toyota fuel system part, but that's another story.)

Like some HAMB'rs have pointed out, cross-steer isn't always the way to go.
Whether for looks or tradition.
A well set-up side steer car will handle just as well and in fact when I started collecting parts for my 31 on 32 rails roadster I was planning on side steer.
Mainly for header clearance etc. in the engine bay.

I couldn't find a decent steering box and I had a good powder coated Vega box sitting on the shelf so I gave in to temptation and now have another cross-steer car.

Makes no never-mind, a rose is a rose is a rose....

 

You guys have it pretty much covered, but here is a cool website with drawings of some different linear restraint type mechanisms. Check out the russell link- it's a little simpler than the watt's....

http://www.brockeng.com/mechanism/

Matt

 

It's because Pete Chaporis back in his Pete & Jakes days put it on that side and every streetrod shop everywhere uses his kits or copies them thus making it the de-facto standard. And now you know the rest of the story...

 

Just got back home from out of town and dug into my books. Carrol Smith touched on this in Tune to Win, chapter 14, starting page 155 and running over most of page 156, here's the last paragraph.
Quote:

"The roll center of an unconstrained beam axle is at the axle center under all conditions. Add a Panhard Rod and the roll center becomes the intersection of the Panhard Rod with the vehicle centerline. With any practical layout, this means that the addition of a Panhard Rod will lower the roll center, which is a good thing, as it is too high to begin with. In order to limit axle movement to the maximum practical extent and to keep the roll center as constant as possible, the Panhard Rod should be as long as possible and should be horizontal at ride height.


Slightly off topic, but reviewing the Smith book explains why when I've never liked the installation of Panhard Rods mounted above the axle to a pinion bracket. First, the Panhard Rod is much shorter than it could be (usually about half the width of the frame inducing more lateral movement than necessary and second, with the Panhard Rod mounted above the axle, the roll center is being raised, not lowered.

 

Everybody should check out this site.......

 

Carrol Smith's book is a book everybody that builds cars should own.
pages 135 to 138 list what factors change the roadholding of the car, in what way, and possible fixes.
Mine automaticly falls open on these pages...

Tune to Win, Carrol Smith, ISBN 0-85045-808-0

Another great book is

Race & Rally car source book, Allan Staniforth, ISBN 0 8549 317 5

And you are right about the stubby little "street rod Panhard kits".
From a geometry point of view, they seem total garbage to me...

 

More from the Smith book.

Quote:

"The Panhard Rod is as simple as anything gets. A tube, with a pivot at each end, is attached to the chassis at one side of the car and to the axle at the other, thus effectively constraining (although not totally eliminating) lateral movement. Ignoring structual deflection which should be eliminated by design, lateral movement of the axle will restricted to the horizontal component of the arc described by the end of the Panhard Rod attached to the axle as it swings. For this reason, the Panhard Rod should be made as long as possible. For this reason also, and to keep the roll center height as constant as possible, the Panhard Rod should be parallel to the axle at ride height. The roll center of a beam axle with a Panhard Rod is located at the intersection of the Panhard Rod with the vehicle centerline. Since the Panhard Rod is asymmetrical by definition, it cannot remain horizontal with axle motion and so the roll center height changes as the vehicle rolls- and it changes differently in right hand turns than it does in left hand turns. If the Panhard Rod is connected to the chassis on the left side and to the axle on the right, then the roll center will rise during a left hand turn and vice-versa. This, in itself, will cause more load transfer to the right rear tire when exiting a left hand corner. For this reason it is normal practice to attach the Panhard Rod to the right side of the chassis for cars that normally turn left and to the left side for cars that normally turn right and thus to use the asymmetry to reduce lateral load transfer on corner exit."

I think this probably comes close to answering the original question posed in this thead.

 

.........

 

Ok, if I read this right it doesn't make any difference which side the panhard is on for street cars except for the bit where the arc's horizontal travel from drag link and panhard is additive when the frame bracket is on the opposite side of the steering box and subtractive when on the same side.
Affecting bump steer and not roll centers.

Roll center/centers are a separate deal.
Which brings up the question of how to find roll center when front and rear panhards are used?
In the majority of cases front and rear panhards are at differing heights.

Seems this would be an ok deal for sprint cars and the like that run CCW on circle tracks.
Torque is going to unload the right rear wheel anyway - unless you're running an engine that rotates in the opposite direction from normal.

 

Remember that Sprintcars run a device called 'Jacob's Ladder' instead of a panhard bar to locate the rear axle and ensure the car does what it's got to do. The front axle is located using a panhard bar.

Roll centres are pretty much always different front to rear.

recently I've been playing with a system we call 'Active Stabiliser' that just confuses matters even more. But boy does it work well to keep the car flat during cornering.

 

Tell me more, Carps...

 

It don't make a diddly fuck ,which side the rear Panhard/track bar is mounted to.

 

Are you familliar with the actuator unit used in Electric Power Steering (EPS)systems?

This is the electric motor that fits between the steering wheel and rack. It takes the wheel input and transfers it to the rack only faster and with no mechanical connection to the steering wheel.

Well, imagine a suspension stabiliser bar that's cut in half with each end fitted into one of these electric motor units. Movement at one end of the bar is transferred by the motor to the other end, in whatever direction and at whatever speed and power is required to keep the suspension flat and stabilise the car. Now, this might sound like a relatively simple modification of the way the stabiliser bar is meant to work anyhow, and you'd be correct. But this is more effective because the movement at the opposite end of the bar can be varied dependent on the size and velocity of the 'bounce' at the road wheel. So where a regular bar might trnsmit about 10% of the movement from one end ot the bar to the other, this system can transmit 100% or if required more or less and do it in a heartbeat. It can also drive the end being affected by road conditions in whatever direction is required to resist, the impact of a pothole or bump therfor controlling wheel movement and helping maintain tyre grip.

However, and this is the best bit. An action at any one end of either front or rear stabiliser bars, can be transmitted and turned into an appropriate reaction not just at the opposite end of thesamme bar but at any of the other three stabiliser bar ends, or road wheels. In other words, as well as the right front wheel reacting to an impcat at the left front wheel, which would make the car pitch, and transfer weight away from the rear tyres to the front, maybe with more to the left front than the right front, thius unsettlying the car. This system ensures that the movenet at the right front is equal to the left if that's what's required to maintain maintain equal weight on both front wheels to keep the car balanced and parallel to the ground across the axle. In addition, the rear is made to squat at the same time, thus eliminating pitching motion completely.

So, the system keeps the car totally flat and stable ensuring optimum grip is maintained at each wheel, for absolutely stunning cornering performance.

When Colin Chapman introduced his ratheromparatively crude version of this technology to his F1 car, it was outlawed almost immediateley because it gave him an advantage that made the lotus unbeatable, despite the additional weight and complexity of his computer controlled hydraulic suspension units .

The system we have is much more sophisticated, adds almost no additional weight and both the technology and hardware are well proven in service over a number of years, albeit in different aplications.

The motors look a bit klunky mounted on the stabilisers and in our application the main processor and control unit means the spare wheel has to go, coz it fits in the spare wheel well, but with todays run flat tyre technology, that's a no brainer.

Now imagine it coupled to technology our Vehicle Dynamics Integrated Management system (already available in the new Lexus GS430 models, BMW also have a similar system) which can maintain the cars direction and grip by taking over brake and steering control (feels weird not to be steering, but it works a treat) and you have a car that can be cornered at insane speeds with total control and very little sensation of movement other than the incredibly high G forces experienced by passengers.

And yes folks, it's advanced enough that it'll be in the market very soon.

Too all you haters of high tech, sorry for this digression from ancient tech, but I'm only answering a question.

 

Wow...
Very cool.

Colin Chapman was the first guy I thought of when I read your other post.

Here is something I've been wondering about, and maybe you can answer this for me.

Isn't a swaybar nothing but a coil spring thats uncoiled?

And because of that, could it benifit from having its own Shock absorber?

 

Yup, just like the much maligned Torsion Bar spring common in MOPAR products, however as a stabiliser it doesn't support the weight of the car.

An alternate method of achieveing the same result we have, might be to use a computer controlled hydraulic link between the stabiliser and suspension unit.

The Toyota Electronically Modulated suspension systems used for some years in many of our luxury and sports models, like Supra, uses a computer controlled hydraulioc or air spring unit which is varied to maintain level. It's effective but heavy and not near as quick to react or accurate as this new system. It's more like an evolution of Chapman's original set-up.

There's no need to add a damper to the stabiliser, since it should be a part of the suspension system anyhow. However, dependent of how the stabilsier is attached to the suspension arms, at what point the stabiliser actually starts to effect suspension movement. In the event the link is attached directly beneath the spring on say a coil over spring./damper unit, it will start to affect suspension movent pretty much at the same time as the spring. However, if the stabiliser is outward of the spring and closer to the point where the tyre contacts the road, it will have some effect before the spring and damper unit starts to do it's job. Likewise, it that point is inboard from the spring, it will start to work later and so it goes. On a road car this is not so critical as it might be on a racer, but how wnad where the stabiliser attaches to the suspension unit can have a profound effect on the vehicle's handling.

 

Yeah, I ment on a Road Car.
On a Racer everything would be in play free pivot points and Rose joints.
But Ive seen some pretty hefty Sway bars with sloppy rubber mounting points on road cars, so I was curious about that...

 

yup, the rubber is used to absorb Noise, Vibration and Harshness which usually means a serious compromise. Likewise many production cars use soft rubber bushings in the suspension pivots for the same reason, especially in mono body cars where any vibration or harsheess is transerred from the road, thru the suspension arms directly into the passenger carruying structure, where it becomes serious NVH.

Engineering a bush that'll absrb NVH whilst controlling suspension movement is not cheap and that's one of the reasons cars like BMW have what seems like tight suspension yet they also seem to move a lot on the bushings. If you watch closely, they'll rock back and forward on the busings but not side to side, lots of compliance under braking and to absorb road shock, but very little lateral movement to keep things tight for cornering performance.

Others, use a sperate subframe with big compliaant rubbber mounts to isolate the mechanical components from the body and allow use of fairly tight suspension busings for good dynaamic control.

Ford Australia's Falcon has a very narrow rear stabiliser bar with the pick up points on the lower control arms close to the inner pivot point. I often wonder how it does anything, but fact is the system works, which proves that book learned theory is not always right and the real answer lies in getting the sum of all the parts to work together effectively.

Which is somethingg I was taught by the very same Carrol Smith mentioned above. he also taught me that instinct and gut feel was more often than not right, but even then you still had to build and test in order to prove it.

 

??Stabiliser mounting locations??

I understand the ability to react faster with the link
inboard/outboard of the coil, but I don't understand why
closer to the road is better. Would you explain that a little
more.

Also what is the optimum mounting location to the body,
does it matter so long as the bar is stable?
I have seen mounting with 1)the bar mounted to the
frame and the links going to the axle and 2) the bar
mounted to the axle and the links going to the frame. Is
there a benifit of one over the other besides space
avaliability and unspring weight??

 

Don't leave me hanging, this is real tech here.

 

I don't believe I said it's better. fact is what works is dependent on a number of things such as suspension arm design and location of suspension arm pivot points. As I did say, the current Ford rear system on first appearance doesn't seem to make any sense and goes against aall the rules, but it works, so the rules really don't matter for much.

I'll try and grab a few minutes to draw some pictures, since that's the easiest way to show the differences.

Again there's various issues come into play here, such as the length of bar between the pivot or chassis mounting point and the suspension arm connection. Different leverage will generate different results.

Again it'll vary dependent on the application. For example, on my old Holden, the front stabiliser is mounted solid on the lower wishbones and the mount where it attaches to the front subframe rails is designed to allow fore and aft movement. The complete opposite to a textbook set-up, but it works great.