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MG MGB Technical - What is a Pan hard rod?

I see these talked about on this site but really now very little about them. I think it has something to do with traction at the rear end. Is it a british term?
Bob Ekstrand

http://en.wikipedia.org/wiki/Panhard_rod -
"not normally used with a leaf spring suspension"

MGB man changing to coil springs, so is fitting a Panhard Rod- http://www.vord.net/cars/mgb_mods/rear_susp/panhard_rod.htm
Geoff Everitt

"This arrangement is not usually used with a leaf spring suspension, where the springs themselves supply enough lateral rigidity, but only with coil spring suspensions." Hah! Whoever wrote that knows little about leaf spring rear suspensions. Panhard designed it because of the insufficient lateral rigidity in leaf spring suspensions! In fact, the correct technical name for a leaf spring suspension is to call it a "Panhard Suspension".

Bob-
The single most significant improvement that you can make to your suspension system is the installation of a Panhard rod. People who tell you that a leaf spring rear suspension does not need a Panhard Rod are only partly right. Think of a rear leaf spring as a lever with its fulcrum at the mounts. When lateral forces are transferred through the springs during hard cornering, the axle and the springs attached to them tend to move laterally across the bottom of the chassis. The only thing restricting this lateral movement on most MGBs is the spring mounting bushings at each end of the leaf springs. As long as the bushings are not worn or degraded, this does not present a serious problem during normal, casual driving. However, if the bushings have become worn, perished, or ovaled (as in the case of old rubber bushings), the fulcrum effect makes it easier for the axle attached to those springs to move laterally. This results in the front and rear wheels being out of alignment. Due to the Panhard leaf spring design that incorporates the use of rear spring shackles, as one spring flattens its arc upward and its opposite counterpart extends its arc downward, the leaf spring that is compressing effectively lengthens rearward on its shackle and the attached end of the axle moves to the rear along with it while the opposite leaf spring is that arcing downwards effectively shortens on its shackle, moving the other attached end of the axle forward. As the rear axle becomes diagonal to the chassis, the resulting thrust angle of the axle worsens both understeer and torque steer. When the lateral forces are high (as during hard cornering), both the lateral and the directional misalignment of the rear axle increase, resulting in increasingly serious torque steer which, when amplified by the serious misalignment caused by lateral movement of the axle, results in what is called ‘Snap Oversteer’ when the rear axle contacts its bump stop. This should not be confused with ‘Spin’, which is usually caused by a loss of traction resulting from the lifting of a rear wheel. An Original Equipment rear stabilizer bar will not only help to reduce body roll, but will also help to reduce this compound misalignment by virtue of its resistance to lateral movement. Adding a Panhard rod will all but eliminate it. With the Panhard Rod maintaining the lateral position of the axle you need not install hard polyurethane bushings into the leaf springs in an attempt to limit the fulcrum effect of a swaying rear axle. All that harder bushings would do in such a case would be to transmit more wheel vibration, noise, and road shock. With a Panhard Rod, you can retain soft bushings and have the best of both worlds. Before you mount a Panhard Rod, you should do a four-wheel alignment. This will guarantee that the mounting on the body will be properly located.

Be aware that the height of the Panhard rod helps to determine the height of the rear roll center. The roll center is an imaginary point around which the rear of the car rolls. The height of the rear roll center, and the front as well, is critical to handling. When you lower the Panhard rod, the rear roll center will drop. A lowered rear roll center promotes side bite at the rear, which tends to tighten corner handling. However, an extremely low roll center can generate excessive body roll, which in turn can cause suspension geometry problems. In addition, excessive body roll can delay corner exit acceleration. It should be noted that the roll center also moves downward whenever the angle of the Panhard rod is increased and thus moved downward. During cornering, the body of the car exerts a side force on the rear axle and tires through the Panhard rod. When the Panhard rod is level, it transmits a wholly lateral force to the rear tires. However, when the Panhard rod is angled downward, it transmits a partially downward force to the rear tires, and rear traction is then enhanced. Conversely, when the Panhard rod is angled upward, it transmits a partially upward force to the rear tires and rear traction is somewhat lessened. A good rule of thumb is to keep the height difference of the mounts of the Panhard rod to within 10% of the length of the Panhard rod.

The location of the mounting point of the Panhard rod, ahead of or behind the axle, determines whether the mount will move up or down during deceleration or acceleration. During deceleration, the mounting point drops if the mount is ahead of the axle, but raises if the mount is behind the axle. It should be noted that during cornering, whenever the Panhard rod is angled downward to the right, a front-mounted Panhard rod resists axle wrap-up under acceleration and enhances axle wrap-down during deceleration. A rear-mounted Panhard rod gives opposite effects. However, in practice the effects upon handling appear to be minimal.

By configuring the Panhard rod with the body mount on the left-hand side of the car, the effects of engine torque on corner exit grip are minimized, allowing you to apply power earlier in the curve and thus get a jump on the competition down the straightaway, no matter what direction the corner is. If the Panhard rod were to be mounted with the body mount on the right there would be a much bigger disparity between left and right hand cornering ability. This would effectively make you choose between setting the car up to exit either left-hand corners or right-hand corners, and live with an under-performing car in the other direction.

One thing that you will notice after installation of the Panhard rod is that the steering response will seem to quicken and the rear end of the car will seem to be lighter on roads that offer reduced traction. This is due to the fact that there will no longer be any delay in response caused by the shifting of the body over the axle. You also may notice that the rear end of the car has a greater tendency to break loose during hard cornering. If this occurs, you will need to upgrade your tires as this type of suspension modification is intended for performance, and 60,000 mile treadwear family sedan tires just will not do! If you need a Panhard Rod that is adjustable in order to accommodate mounting onto either wire wheel or solid wheel Salisbury tube-type rear axles, you can get one from the MG Owners Club over in the UK. They have a website at http://www.mgocspares.com/
Steve S.

Pronouced: Pan-ahr
Cleve

"One thing that you will notice after installation of the Panhard rod is that the steering response will seem to quicken"

Not directly related, perhaps, but when I recently replaced worn out rubber bushes in the rear spring shackles with blue polyurethane bushes, the steering seemed to become a little lighter and more responsive.

Tore

Tore

Bob,
A Panhard rod is a bar fitted to stop the rear axle moving sideways as the car goes through a corner.

One end attaches to the body and the other to a point on the axle. Both ends have bushes or bearings to allow some degree of movement but it is very limited.

The aim is to stop side loading on the rear (leaf in the MGB) springs so they are less likely to bind.

The rod itself must be fairly substantial since it is taking most of the cornering forces in a straight line and most are as long as will fit in the space since the longer the rod the less it will move sideways for a given vertical distance.

As a small historical point it dates back to the original Panhard cars built around the late 1800's and into the 1900's. The French firm was eventually taken over by Citroen who are now part of the Citroen PSA group.

Pete.
Peter Thomas

This thread was discussed between 04/06/2009 and 06/06/2009

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