Panhard bar

[97car]

I have a question, and don't remember all of this stuff. My panhard bar mounts to the frame on the left and the rear end on the right. If I lengthen it it will move the rear end over to the right and create more rear stear correct? The other question is the bar is level with the rear end, what does raising it or lowering it do with the bar mounted on the side it is to the handling?

[NickHolt]

My panhard bar mounts to the frame on the left and the rear end on the right. If I lengthen it it will move the rear end over to the right and create more rear stear correct?

If your Panhard bar is mounted to the frame on the left, by lengthening the bar you are moving the frame to the left in relation to the rear end. By doing this you may be putting the rear trailing arms in a bind if the design of the mounts does not allow for that much side-to-side movement. This will especially show up during suspension travel producing unpredictable handling characteristics at the worst possible moment.

 

Most rear suspension setups using a Panhard have equal length lower trailing arms, so there will be little practical difference in rear dynamic roll steer other than what is generated by any difference in the rate of suspension bind between the left rear to the right rear.

 

It's usually best to have the lower control arms run parallel to the centerline of the chassis rather than offset to one side or the other. Then use the angles and/or lengths of the lower trailing arms to produce whatever roll steer effects you are seeking.

 

The other question is the bar is level with the rear end, what does raising it or lowering it do with the bar mounted on the side it is to the handling?

 

In the simplest terms, the height of the Panhard bar above the ground at the centerline of the chassis defines what is called the rear roll center. The higher the rear roll center the looser the car will be in the center of the turn (while not on the brakes and not on the throttle). The lower the rear roll center, the tighter the car will be in the center.

 

While there are differences in the way the Panhard bar handles the forces generated in a turn based on the angle of the bar in relation to the rear end housing, it is usually best to have the Panhard bar wind up basically parallel to the rear end housing during maximum body roll. In your case this would mean that you would need to know whether the left side of your chassis is raising or compressing in the turns. There's a lot more involved (jacking effect, etc) when using the Panhard bar as a chassis tuning tool. We cover some of these parameter in my suspension seminars.

 

Nick

[Wayne Walker]

Nick, you brought up some very good points about angles. You didn't mention that moving the rearend right or left also can make the car looser ar tighter.

[NickHolt]

I much prefer to use rear trailing arm angles that keep the car tracking true until the body starts to roll. That way you get the most out of the suspension geometry.

 

I realize that many divisions are not permitted to do much to their rear end setups and would not be able to change the rear trailing arm angles enough to produce the desired results. In that case, you are exactly right. By moving the RR backward or the LR forward, or both, you produce oversteer. By moving the RR forward or the LR backward, or both, you produce understeer. Unfortunately, it also causes the car to scrup speed down the straights as the rear tries to dog walk.

 

Nick

[Truck99]

Nick, I took Wayne's info to be referring to the manner in which big panhard bar changes will actually move the rear end left and right laterally in relation to the chassis.

[Wayne Walker]

Correct ss99. lateral location can siqnificantly affect the handeling. Nick, I also understand what you are referring to. We use trailing arm angles to move the rearend ALL over the place on an IMCA Modified(4-link). We also use angle in the J-bar for cornering changes.