TRACKBAR, anyone here run one?

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Lateral deflection of the leaf spring's main leaves combined with compliance in the spring bushings can be significant. I can't even dive the Valiant into a corner very hard yet and I can use up the ~3/8" of clearance between the inner fender and the tire's sidewall. Some form of lateral location has been considered just to stop the rubbing as I can't 'bump' the inner fenders any further out of the way.

Late model Mopar SUV's have a Watts Link under the rear, I've watched a few going down the road.
 
ntsqd said:
Lateral deflection of the leaf spring's main leaves combined with compliance in the spring bushings can be significant. I can't even dive the Valiant into a corner very hard yet and I can use up the ~3/8" of clearance between the inner fender and the tire's sidewall. Some form of lateral location has been considered just to stop the rubbing as I can't 'bump' the inner fenders any further out of the way.

Late model Mopar SUV's have a Watts Link under the rear, I've watched a few going down the road.
Click to expand...

Tyres deflect a lot when hard cornering.....my front tyres rub on the bottom of the top BJ's on my daily driver, even though they are 3mm ( 1/8") away....outwards, not sideways.
Tyres are Bridgestone Eager SF340 in 235/60R15.
 
cjh, Yes, tires do deflect quite a bit. When I was running 60 series 15's they'd rub the leaf springs on occasion.

Have a look at [ame="https://www.youtube.com/watch?v=ZZ1uCH9ay1k"]this [/ame]video at 1:24
Looks like the tire is gonna get pulled off the bead..:wack:

I'm not sure [ame="https://www.youtube.com/watch?v=Lev7Ifrln_g"]this [/ame] one shows axle movement or tire deflection.
 
BTW, if you bother to caclulate it out, the lateral movement of the end of a 4' long panhard rod/track bar with + or - 3.5" of vertical movement is <0.15" which is <5/32" of lateral movement. So the idea that it will produce a lot of side motion as the suspension moves up and down is a false perception that is taken way out of proportion. You get far more side flex in the tire sidewalls than that!

And I'll repeat here again....

There is another critical function of the track bar if you are really engineering for handling. It allows you move the rear roll center up and down and thus change the roll axis of the car, which can be used to help tune understeer/oversteer. With the standard leaf spring setup, the roll center is cannot be moved without changing shackles or re-arching leafs, and is usually higher than desired. If you use rather loose spring bushings in the rear springs and hard bushing or heim joints in the panhard rod, the panhard rod takes over all of the side-to-side locating function and the rear roll center is determined by the panhard rod settings, not the leaf spring connections to the chassis.

As for the panhard bar tearing up the body, that is another false perception. A number of unibody cars have had these as stock items; all of the Opel GT's, Kadetts, and 50 series unibodies had them. I have raced these for years and years in rough conditions, slamming against banks, rocks, and logs, and the panhard support or surrounding body work never bent or budged. Any decent amount of load spreading and thought in attachment will avoid any issues.

If you have never used them or raced with them, I can understand how the perceptions can get out of hand, but it makes little sense to predict doom and gloom on such an item if you have not used it.
 
Agent_Orange said:
I understand why you would see this on a coil over type rear suspension, and yes there is an amount of side movement within the leaf spring suspension. So the point is, after upgrading the springs from stock, how much would a panhard bar really help the hard cornering, or yaw of the car?
Click to expand...
Please understand that there is more benefit in the panhard rod/track bar than just getting rid of spring twist and lateral dislocation of the body; those benefits alone are more than you realize if you ever really drive cars with and without track bars (or any good lateral location) enough.

The other very real benefit is in tuning for oversteer and understeer, which, if you care about handling (aren't you the guy who wants to beat the 'vettes?), is another important tool in your tool chest of chassis tuning. There is a very real reason that the modern NASCAR cars all have adjustable track bars, and that is it! You get this with or without leaf springs, coils, etc. If waht you have a is good enough, then don't bother. But if you are serious aobut beating those 'vettes.......
 
Is there a universally accepted design for a panhard bar? Or better yet who/what/where would be a good source for design?
 
The bar itself is very simple: a long tube with short tubes welded on the ends configured as 'eyes' on the end of the long tube. Bushings go into these 'eyes'.

The location of the rear roll center is determined by where the rod/bar is vertically located. Generally, just under the axle center line is the norm for the axle end, and horizontally across the chassis from that point for the fixed end. The construction of the fixed pivot, which hangs down from the rear subframe is the most complex bit and is typically a fabricated, tapered box welded to the floor and subframe.

Here is a link to panhard fabrication for Opels. The guy doing the posting, RallyBob (Bob Legere in CT), is pretty darned knowledgeable. You will need to register on this site to view the pix but this is a very good tutorial. BTW the part about crashing if the panhard rod or mounts fails is less applicable with leaf springs as you still have some side axle location. But the car is still going to experience quite a change in handling if it does. I have rallied for a long time with panhard rod equiped cars and never broke one.

Your car's handling will change noticably with this, as the rear roll center will go down a few inches. The car will be quite a bit less tail-happy (less prone to oversteer), and you will need less front roll bar (a smaller diameter front roll bar). At this point, it should be easier to tune F/R balance with spring rates. The hard part of tuning this suspension is the limited selection of T-bars and leafs.

BTW....I just read your avatar and had to laugh!

And, you can look up rear roll center diagrams on the internet to see the difference in a leaf vs panhard rod with a live axle. See if this image works for you: http://www.chevelles.com/showroom/data/516/medium/ROLL_CENTER2.jpg
 
nm9stheham said:
The bar itself is very simple: a long tube with short tubes welded on the ends configured as 'eyes' on the end of the long tube. Bushings go into these 'eyes'.

The location of the rear roll center is determined by where the rod/bar is vertically located. Generally, just under the axle center line is the norm for the axle end, and horizontally across the chassis from that point for the fixed end. The construction of the fixed pivot, which hangs down from the rear subframe is the most complex bit and is typically a fabricated, tapered box welded to the floor and subframe.

Here is a link to panhard fabrication for Opels. The guy doing the posting, RallyBob (Bob Legere in CT), is pretty darned knowledgeable. You will need to register on this site to view the pix but this is a very good tutorial. BTW the part about crashing if the panhard rod or mounts fails is less applicable with leaf springs as you still have some side axle location. But the car is still going to experience quite a change in handling if it does. I have rallied for a long time with panhard rod equiped cars and never broke one.

Your car's handling will change noticably with this, as the rear roll center will go down a few inches. The car will be quite a bit less tail-happy (less prone to oversteer), and you will need less front roll bar (a smaller diameter front roll bar). At this point, it should be easier to tune F/R balance with spring rates. The hard part of tuning this suspension is the limited selection of T-bars and leafs.

BTW....I just read your avatar and had to laugh!

And, you can look up rear roll center diagrams on the internet to see the difference in a leaf vs panhard rod with a live axle. See if this image works for you: http://www.chevelles.com/showroom/data/516/medium/ROLL_CENTER2.jpg
Click to expand...

Thankyou much sir, I appreciate your help. Correct me if I am wrong here, but a panhard bar will eliminate the need for a rear sway bar...correct?

Also, I was just looking at the diagram on chevelles.com, and I think I finally understand where the panhard bar lowers the roll center. Let me use nascar as an example. When there is an adjustment made on the trackbar, what they essentially are doing is raising or lowering the point where the panhard bar connects to the chassis. right? or am I misunderstanding the concept.

and wouldn't the panhard bar in itself create a lateral movement in the rear end as the car digs in the corner? or is the idea that a stiff enough suspension would not allow enough squat in the rear to affect the geometry.
 
I'm not aware of a panhard bar kit, but that most likely means that someone will know of one and post a link. You can buy parts and pieces from the various race car parts vendors if you're willing to go with SRE's for the joints. It becomes more difficult if you want something better sealed from road grime. First step up would be to use some Seals-It washers with the SRE's, but any off-the-shelf bracket available may not have room for them. Next step up would be to use tie rod ends for the joints. If welding is an option then cut the steering arm off those old LBJ's and use them to fabricate some mounts for a panhard that uses the OE tie rod ends and then cut an adjusted sleeve in half and weld each end to a long enough tube. Or you can buy the right taper reamer and put that hole in other steel parts. Could go lighter duty parts and use TRE's from an ATV. Some (all?) of those do not have the taper, they fit a straight hole. Maybe those for a UTV rival the size of the OE TRE's? No idea.
 
Agent_Orange said:
a panhard bar will eliminate the need for a rear sway bar...correct?.
Click to expand...

No. An (anti) sway bar serves a completely different purpose. They basically "pull you up" by your own boot straps depending on which side you want to look at.

As the car leans DOWN onto the suspension on one side, the (anti) sway bar transfers this movement to the suspension on the OTHER side of the car, "picking up" the suspension on that (high) side of the car, as if letting a jack down

Otherwise, the unloaded springs on the high side are "helping" to lift the high side up and "roll" the body over


This causes the car body to stay "flatter" through a turn with less body roll, but doing so with less stiff springs

Really, all a panhard bar is doing is attempting to keep the rear axle centered in the body. If the leafs were "wide enough" and stiff enough, and the bushings and shackles heavy enough, they would do the same thing.
 
Del, you are missing the effect of the change in the roll center with the panhard versus the stock spring mounts. These cars tend to transient oversteer badly when thrown hard into a corner, due to the higher rear roll center of the spring mounts, and the panhard rod will help reduce that 'tail happy' tendency a lot. And, I can promise you that the centering consistency of the panhard rod will be far, far better than the stock springs. The small lateral movement of the panhard rod is a consistent movement; the opelgt.com link below discusses the left/right tendencies more. The watts linkage eliminates this but is a lot more complex.

OP, no the rear sway bar may be needed. With the roll center lowered and less oversteer, you will be putting a front anti-sway bar in (if you don't have one) and then see where you are with oversteer/understeer. The overall car's roll resistance will be a combination of the spring rates front and rear (t-bar and leaf) and the 2 roll bars. If you want it to corner flatter, you add front and rear bars and adjust the stiffness between the front and rear bars to manage over/understeer. Of course, since you want to keep expenditures minimum, then you don't want to buy a variety of sway bars; the panhard rod, if adjustable in height, allows you to tune around that some.
BTW, the adjustability probably is the one thing to jettison to reduce complexity, but it might save a sway bar change.
BTW2 For auto-x, the transient over/understeer will be very important, and that has a lot to do with the shocks. So you can set the static under/oversteer but you will still have shocks to work on.

And, yes, that is why the NASCAR guys are doing this, with the vertically adjustable chassis connection to the bar/rod.

Don't use tie rod parts for this. Use a 3/4" (1/8" wall, it's too heavy but can be threaded for a heim joint in one end) mild steel tube, weld on one tubular end for an eye and use a poly or rubber bushing in that, that fits over a stud on the axle connection (which can be a strong stud welded on the lower spring plate, and then put a 5/8" threaded heim joint in the other end that fits a bolt in the chassis mount so you can get it centered. This link, which I forgot to provide above, is a really good thread on these details.
http://www.opelgt.com/forums/perfor...-panhard-bar-roll-centre-geometry-racers.html

But the points on weather proofing are well taken; the heim joint is not weather proof.
 
I have to disagree on not using TRE's for a panhard bar. I've looked at it from every angle that I can think over quite some period of time and I see no reason that they can not be used. If they're good enough to steer with, they're good enough for a panhard bar. Compared to an SRE they *might* be a little less precise, but if a person is considering this option they are more likely working with a street or street/track car and not a pure race car. For a pure race car I too would go with SRE's because the dirt & grime issue isn't really an issue as usual race prep will deal with it. For a street driven car it is rare to non-existent that they see that level of prep.

Most ideal would be that that the tube's OD & ID are sized such that the builder could tap the tube directly for the TRE ends, but that would require that they be able to first find and then be able to afford a set of LH & RH taps that usually are some obscure diameter & pitch. I don't see any problem with sizing the tube such that the adjuster sleeve will tightly slide inside the tube and be welded into place at the end and with a couple Rosettes. That is no different than buying tube ends for SRE's and welding them to a tube. If the TRE's chosen happen to have threads that there are tube ends made for, then I'd use them instead of the adjuster cut in half but as I mentioned TRE's can come in odd threads and finding tube ends that will work is not too likely. For instance, I know of no tube ends in 11/16", they go from 5/8" right to 3/4" I can't remember ever seeing an SRE with 11/16" threads, they too jump from 5/8" to 3/4", but that is the size of the threads on the TRE's on my '65.

One end in rubber is a good idea from an NVH (Noise, Vibration, Harshness) point of view. It will damp out any road noise & vibration being transmitted up the bar to the chassis.
Could use one of these for some NVH reduction (They're urethane rather than rubber, which isn't quite as good at NVH reduction):
http://www.kugelkomponents.com/zencart/index.php?main_page=product_info&cPath=50&products_id=183
http://www.kugelkomponents.com/zencart/images/adjuster_plain_large_multi_sampleimage.jpg

Or the straight version:
http://www.kugelkomponents.com/zenc...id=168&zenid=43ece8f42cb41a9080f2c489059423df
http://www.kugelkomponents.com/zencart/images/adjuster_plain_large_fixed_sampleimage.jpg

Some circle racing car links:
http://portcityracing.com/search?Keyword=panhard
http://www.colemanracing.com/Chassis-Suspension-C14.aspx
http://www.afcodynapro.com/store?search_api_views_fulltext=panhard
http://www.speedwaymotors.com/search.html?query=panhard
 
lets see if i can word this where you are able to understand what i'm trying to say.

The point where where the panhard bar mounds to the axle, how do i determin how much above/below the axle to this mount needs to be. are we trying to accomplish a trackbar that is parallel to the ground? or is there a degree that is considered to be a sweet spot? if adjusting the mounting point up or down affects the roll center of the car, can the bar being too low make the car push in the corners?
 
When setting up panhard bars for live front axles the usual is to set them such that they are slightly down towards the axle with the goal being that they are horizontal at the mid-point of the 'frequent travel range' (i.e. the normal motion range seen on pavement). This RoT is probably appropriate on a street car as well.

The Roll Center (RC) of a panhard bar system is defined as being where the center-line of the "Line of Action" (LoA; i.e. the straight line btwn the pivot points) pierces the chassis' center-line. Moving either end, or both, up or down will move that piercing-point and change the RC's elevation.

As to where you want to start with it, I'm not the guy. I'm not up enough on street car handling to even make a WAG. W/o the panhard the RC of a leaf sprung suspension is located at the height of the axle shaft center-line. Could start there and give yourself plenty of adjustment in both directions.
 
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