Is an aftermarket panhard rod with polyurethane bushings beneficial for drag racing on a non-lowered car? I know the rod is good for road racing/auto-x.

 

Ummm, I'm not an expert or anything, but since the panhard only controls lateral motion, I don't really think that it will make a big differance. It could help if you're pulling the front tires on a launch, but until you hit those power levels it shouldn't really matter.

 

You don't want any flex. When the car launches it puts stress on every part of the rear suspension and you want your shocks and springs to work as they are supposed to. You obviously want all of your power to get to the ground as soon as possible. If you have aftermarket LCAs then the flex will be transferred to the panhard bar. As cheap as they are to buy in the aftermarket its silly not to have one..

--Alan

 

You sure about that? The back end squats on a launch. It would help a bit for street and drag racing. It doesn't matter what power level you have, it will always help. The LCA's are going to transfer the tension and power to the panhard rod, creating the squat. Getting an aftermarket LCA and PHR would stop the majority of the squatting and put force on the tires, making more traction.

 

MyShibbyZ28 and ABA383 are on the right track. When you accelerate or brake you are putting a side load through the panhard rod. These loads are created from the arc the panhard goes through during acceleration squat and brake dive (lifting of the rear tires). This does not even account for the engine torque creating torsion forces through the power-train which will also put lateral forces on the chassis. This is a simple explination without much detail.

I realize they are different vehicles but this will give you an idea of the type of forces the rear end will see during only acceleration. We built many years back a fixture to measure how much the chassis moved over the axle laterally on a Mustang. Now keep in mind the Mustang uses a four link rear suspension without a panhard rod. Ford tries to locate the rear-end by using 4 apposing links, two upper and two lower. The rear end during our test actually moved over 2 inches on acceleration alone. Yes the Mustang has more compliance but the rear end only moved 2.5 inches during hard cornering. What this tells us and you is the lateral forces are present during acceleration and braking along with cornering. Good luck on your project.

 

Heheh I'll keep my mouth shut unless I'm totally sure next time. At least I learned something. And you guys are definently right, as cheap as some of the PHRs are how could you pass on at least upgrading it to somethign other then stock?

 

We've all been there at some point Besides, have to start somewhere.

Anywho, for some added info to what hotpart said. Take a chopstick and put it in the corner of a wall so one end is where the floor and wall meet. Have the other end diagonally in the air, just like how a panhard rod is diagonally on a car. Take something hard and flat, like a book and put it against the end that is in the air. Hold the book with one hand, and try and push down the end against the book with the other hand. Make sure the book doesn't move. After a certain amount of force the chopstick starts to bow and flex. That is what the stock panhard rod does. It flexes and gives because it can't take the stress being put on it. Aftermarket panhard rods are stronger and hold, causing the weight and power of the car to push down on the axle, essentially pushing the tires down harder, therefore achieving more traction.

For lower control arms; it's the same, but they are more for horizontal movement. The axle wants to move forward, not the car. So the axle, when given power and traction, starts to move forward, but the lower control arms stop it since they are attached to the rest of the car. So therefore the axle is pushing on the LCA's, which pushes on the car, which moves it forward. Same thing goes for flex and stress. The stock LCA's bend and flex, which means you lose some power in that flexing/bending. Stopping the flex and bend essentially means less power is being lost in the LCA's, and instead gets put into moving the car forward.

Now, say you have aftermarket LCA's and PHR. Here is basically what happens.

1: punch the gas
2: LCA's take the force and push the car forward
3: car wants to rock back from force of taking off quickly
4: back end squats down, panhard rod pushes down on axle
5: axle has no easier way to move than to push the car forward.

The whole main point of the PHR and LCA's are to force the axle to the ground and make traction.

ShibbyZ

 

Hmm, I thought it was the torque arm that pushed down on the axle. I know that the LCAs keep the axle from moving forward and backwards. I figured that the PHR was only going to help when in a turning manuver, when a sideways motion is happening. The tires are holding the axle in place, but the body is still trying to move to the side from the sideways g's. The weight of the rear body trying to move would cause the PHR to flex. A stronger PHR would get rid of that flex and keep the axle centered under the car, and keep it from moving to the sides. It wouldn't get rid of bodyroll, that's obviously the swaybar's duty, but it would lessen the sideways movement of the axle.

Now I can figure that when you launch there's so much force going through there that somewhere along the way to the rear tires something is going to push the axle to the side. In that case a PHR would do something, but I always figured that it was far more of an upgrade for handling than for launching. That's why I origanally said the comment about lifting the front tires, because without the front tires on the ground it's up to the rear axle to keep the car in line, and I could just imagine the kind of force that would be on the PHR since it would essentially be balancing the car when it came to the body swaying to the side.

Please correct me if I'm wrong. This is what my idea was for how the rear suspension worked. It's kind of hard for me to explain what I'm thinking here, hopefully you can get the gist of what I'm trying to say.

 

The torque arm does push the axle down, but I'm saying the panhard does too. Everything kind of works together to keep everything lined up right. Did you try the chopstick thing? A pen would even work instead of a chopstick.

Think of the panhard as a "locater" for the axle, it keeps it where it is suppose to be. Wether that is side to side, up and down, or whatever. The LCA's keep it from going forward and back. The torque arm keeps it on the ground yes, but the panhard bar is what forces it to the ground during a hard acceleration (the torque arm does this too, just differently). Think about it, the car would be really weird feeling if you accelerated like a bat out of hell and the body of the car fishtailed while the axle stayed straight.

As for cornering, I actually had no idea we were talking about that . But, yes the G force being put on the body wanting to slide off the axle would cause the panhard bar to flex and what not. A stronger one would stop that, causing the car to stay put better around corners.

edit: a better explaination; there is always lateral force and stress on the car. That is why the chassis flexes and you get those mysterious little dents on the passenger side quarter panel (I have a ton... ) The car is ALWAYS under lateral force, even at idle. If the engine is turning, then the car is wanted to be rolled or twisted in some way, even if it's so minor it doesn't matter. The panhard rod's job is to stop this lateral force, and when you floor the gas pedal, you put maximum lateral force through the axle. Panhard rod essentially stops this, so the car therefore squats, then pushing down on the axle, creating traction.

I hope that helped a little more.

edit #2: the panhard rod doesn't directly push the axle down, the rest of the suspension does that, like spring, shocks, whatever. The panhard rod is indirectly pushing down. Sorry, should have made that clear from the start.

 

Thanks for the explanation. BTW, haven't had chinese in a while so my place is devoid of chopsticks . I get it now. I always figured that the PHR sole purpose was to keep the axle centered during turns, I didn't take into account the fact that it's being worked all the time. I threw the point about handling in there because the original poster said that he believed it was a mostly handling upgrade.

 

This is correct, except for the last sentence. It doesn't lessen sideways movement of the axle, it lessens sideways movement of the body. The axle is staying put around a corner, the body is what is trying to move to the side, since it's not the one with tires touching the ground.

Also correct...just another thing. It doesn't "balance" the body on the axle, it more or less holds it in place. Just refer to this...

and
There, that sums everything up I think...

 

Draw an accurate "free body" dagram of the rear axle, and you will see that the panhard rod can exert very little vertical force on the rear axle. Its got pivots on both ends. As the body comes down, the resolution of forces along the panhard rod will be almost toally horizontal, since the bar is close to horizontal.

The bar simply locates the body side to side over the axle. The things that resist the "squat" are the springs and the shocks.

Keeping the body in line, over the rear axle is important. You don't want the rear of the body moving side to side, while you're trying to drive the car in a perfectly straight line down the track, with minimum steering input.

 

Wow, that was a way better explaination then I could have done.

 

So I'm guessing a new panhard bar would be beneficial for drag racing.