Tried the search...on several websites.

I would like to do a custom panhard bar setup on the Chevelle, but I am pretty new to hardcore suspension designs. Does anybody out there have any tips they could share to get my project started??

Here's what I know:
- The longer the bar, the better.
- Bar should sit about level at static ride height, with half tank of gas.
- One frame mount, one rear end. (Both double shear.)

...and, thats about it.

Can anybody help point me in the right direction. ...Dennis??? ha.

Thanks.

From what I have gathered you know how it works. Dennis did a setup on his car so he might have some pics to show you. Just keep it long and level like you said. I am thinking about setting one up myself. The only problem you should have is choosing the links on the end, which is easy, and figuring out where to attatch it to the rear/car.

When would I fab it up though?? The car is completely disassembled down to the bare frame right now, with new suspension on the way. After the body is back on, and the car is sitting at ride height, would I just weld the panhard brackets so that the bar is level??
-or...
Is there a certain height in relation to the rear end at which the bar should be mounted, and then adjust it so it's level???

You should definately wait until its at ride height like you said, with a half tank of gas. You want it level so that the force is transmitted in pure tension or compression during normal right height. When the car rises or lowers the bar will move +- a few degrees. By having it be level most of the time, the degree difference is minor, so the rear will not move side to side too much. By making it longer, the smaller the degree, which means the less it moves side to side.

So just wait till correct ride height, then fab it up so it is perfectly level and long as possible.

If you are familiar with trig, then you can setup a triangle reliationship and see how much side to side movement there is for how much up and down movement there is with the rear. sin=opp/hyp and so on...

So just wait till correct ride height, then fab it up so it is perfectly level and long as possible.

That just about summed it all up for me right there.

Thanks a lot!

Oh yea, might as well make it strong. And post pics once your done.

Personally I would do the fab work while the body is off because the access is MUCH easier. You can estimate what you want for ride height, remove the rear springs, and cut wooden 2x4 blocks to hold things at the right height.

The one thing I *would* have installed is the exhaust system to insure clearance.

Many PHB installations incorporate multiple mounting points for the bar to provide some adjustment. The height of the bar will determine your rear roll center after all, so you might want to be able to expirement with tuning it once the car is back on the road.

If you make the bar long enough, then you will not suffer too much if it is not perfectly level. The main driver for level is to minimize lateral movement of the axle as the suspension articulates. The long bar will do much more here than the horizontal position and is thus the critical parameter. I might consider starting with the bar out of a late Camaro/Firebird (F body?) and make mounts to fit. This could also be interesting as a starting point (but they only go up to 37"): http://www.speedwaymotors.com/xq/aspx/paging.yes/dept_id.108/display_id.2091/qx/Product.htm

These could be fun as ends: http://www.speedwaymotors.com/xq/aspx/paging.yes/dept_id.107/display_id.1534/qx/Product.htm

The frame mount that Dennis used was pretty crude. I would suggest you check into the kits for Mustangs that are out there to get a better idea of what a frame mount should look like. The Chevy rails are really very flexible back there, so I think it is important to brace and triangulate the mount to the frame rails on both sides.

And of course if you are going to the fun of putting in a PHB then you might also want to go just a bit further and convert to a 3-link setup with a single upper control arm.

More headstart pieces:

http://www.speedwaymotors.com/xq/aspx/paging.yes/dept_id.103/display_id.3381/qx/Product.htm

You haven't really lived until you are driving on a freeway and the upper panhard mount breaks. I have experienced that only once and once is enough.


Whatever you do mount it well! :)

vrooom3440, Are you trying to eliminate the upper control arms with a three link or keep them?

I have thought about a 3-link in the past. The idea still crosses my mind every now and then. I don't think I have enough knowledge of all the suspension geometry and how it works to fab my own 3-link from scratch, just yet.

Does anybody know of any books they would recommend about suspension engineering that would help me with doing my own suspension???

If I can gather enough knowledge about suspension (i.e. 3-links) to the point where I am comfortable with doin' my own setup, I'd definately give the 3-link/panhard bar system a shot.

I've heard that SC&C is developing a bolt-in 3-link for A-bodies. Anybody know anything about this?? I'd still probly rather do my own, just for the whole pride/bragging rights thing.

It really isnt that complicated once you see some pics. Have you tried a search? I know there was a picture just a few weeks back I saw.

And sorry about that last post where I assumed you wanted a three link. I have since changed it, but I agree that could involve a little more fab work. Anyway I found a pic. I dont really think the panhard bar is neccesary though. I dont get that much side to side movement back there with the new bushings in, except for tire wall.

That pic is worth 1000 words. See how it is level and inline with the rear.

BINGO!
http://www.onrails.us/images/phb.jpg
For copyright purposes(not my car) I believe it is Denny's and he is fairly comfortable with suspension design, to say the least...

Yep, that picture is of Denny's El Camino and is not what I would call an outstanding example. Functional yes but not outstanding ;-)

On the stock A-body rear suspension the upper control arms serve both to control axle torque forces AND lateral axle movement. This why they are angled into the center forming a triangle. The point where they meet determines the rear roll center, which is quite high.

The angled layout also means that they must be allowed to move and flex a bit to accomodate the multiple planes of movement. And is why hard bushings, like poly, are not recommended for the upper control arms. But because the design requires flex it is not able to do a very good job of locating the axle. On a similiar design lateral movement of up to 1.5" has been measured during operation. Compare that to a PHB, I believe Denny claimed to be able to run 1/4" tire to fender clearance without rubbing?

The PHB being a lateral axle location device removes the requirement for the upper control arms to provide that function. Which is why many OEM designs with PHBs use a single upper control arm in the 3-link configuration. One concern with running the stock converging 4-link setup with a PHB is that there could be competition for lateral location of the axle between the two different roll centers. The result could at the least result in some binding and at the worst force overloads and part breakage. Denny did not note any issues but he kept the roll center fairly high (reduces the distance between the two roll centers) and had not run the setup very long. Last I heard his El Camino was up for sale.

SC&C is reportedly developing a 3-link setup for A-body cars. As a basic start to some of the concepts involved in a 3-link design you might check out the Fred Puhn "How to make your car handle" book. There are others... some might even be better... but that is what I have on my bookshelf :-)

Vroooom has excellent points. The upper control arms could slightly interfere with the PHB in certain suspension scenarios. Denny also had a very low and stiff suspension setup, so I doubt there was much movement in there.

Looking back, unless you go 3 link, I say just stay with what you have. Install a swaybar and new bushings, good shocks, get it lower, and your car will handle very well. The stock 4 link can be put through its paces pretty well.

Herb Adams "Chassis Engineering" is a pretty good beginners book... Lots of good diagrams and formulas, just don't take some of his theories as gospel. ;)

If you guys try and follow what Denny did, please put those PHB bolts in double shear.

Joe

agreed.

Keep in mind that Denny's El Camino was very (VERY!) low to the ground and that made his mounting much easier. Take a look at mine for a basically stock height example. It's not as easy as it sounds, expecially if you want to run full exhaust. Dennis could also run close tire gaps because he had very stiff springs as well.

Ryan

Thats a cool senior design project! I will be doing mine next year. I think we might have different requirements though. I will look into it, would love to do something with my car.

I was unfamiliar with the term "double shear" so I found this little tidbit for those of us who were wondering what it meant. It appears to me that the picture in Brettd85's pic shows "double shear" with his phb. :)


As it happens I used double shear when installing my rear sway bar. I put tubes and hardened washers on the inside of my LCA's so that the through bolts wouldn't crush the control arms since they are not boxed.


http://www.roymech.co.uk/Useful_Tables/Screws/Bolted_Joint.html

Yea double shear is just when the bolt is required to shear in 2 locations for complete failure rather than one. That is why with a panhard bar you want the bolt to go through a bracket, then the panhard bar, and back through the bracket. So in order for the panhard bar to give way, it must shear the bolt at both sides of the bracket.

I believe in Denny's panhard bar, only the right side of the bar is mounted in double shear.

The thing about your sway bar though charbilly, is the bolts are more in tension than in shear *I think*. Even if they are in purely shear, they will fail at the interface of the control arm/sway bar which is just one location. I could be wrong but I dont believe this is considered a double shear loading. Now if the sway bar mounted on both sides of the control arm, double shear would be the case.

On Denny's PHB both ends are mounted in double shear.

On Ryan's the frame side IS double shear and the axle side is NOT double shear.

The typical sway bar mounting is single shear. There is one shear point for the bolt holding the sway bar on.

Suspension mounting points are almost always in double shear.

It looks like Denny's frame side mount is in single shear. I may be seeing things though.

Yea double shear is just when the bolt is required to shear in 2 locations for complete failure rather than one. That is why with a panhard bar you want the bolt to go through a bracket, then the panhard bar, and back through the bracket. So in order for the panhard bar to give way, it must shear the bolt at both sides of the bracket.

I believe in Denny's panhard bar, only the right side of the bar is mounted in double shear.

The thing about your sway bar though charbilly, is the bolts are more in tension than in shear *I think*. Even if they are in purely shear, they will fail at the interface of the control arm/sway bar which is just one location. I could be wrong but I dont believe this is considered a double shear loading. Now if the sway bar mounted on both sides of the control arm, double shear would be the case.

Actually you are correct. The sway bar is only in contact with the inside face of either LCA. If it were mounted inside the "U" channel it would be double shear. My bad:)

That said, I broke my first sway bar not an LCA. I was rather surprised because my car is strictly a daily driver car.

Yep, my axle mount is not the hottest thing around since it's not double shear, but it is a 3/4" grade 8 bolt. I don't remember off the top of my head right now, but I'm confident the rod end would let go long before the bolt would break (I did get an A on my design :) ). There is also a washer to capture the outer part of the rod end in the event that the bearing failed axially - still not the best but it would keep the PHB in the car long enough for me to pull over.

I'll also add that this design has made it 2000 miles so far without any glitches - with roughly the last 700 miles on nasty Michigan roads. I'm still glad I did it. It's too bad I'll have to put the car away in a week or two.

Ryan

Who is Dennys so I can ask him a specific question ? I want to know the width between the two plate on that prefabbed axle mount.

I'd like to know where he got his hardware.

Also as far as his car bing lowered and opposed to a stock height car. If you switch the prefabbed axle mount to the drivers side, the bracket will point up rather than down so is should give you a nice horizontaL bar.

Denny used to be a regular poster here, but he hasn't been online in over 6 months... I believe he sold his el camino also, but he left the forums before it was sold so he may still have it.

The panhard bar is mounted where it is because that is specifically where he wanted to place his Roll Center Height.

Dennis had to sign off due to the serious addictive aspects of internet forums adversely impacting his regular life. I can often relate.

Based on Dennis' predisposition to stock car pieces, I would guess that the axle mount was a weld on version like this:
www.speedwaymotors.com weld-on panhard bar mount (http://www.speedwaymotors.com/Product.aspx?paging=yes&dept_id=103&display_id=3381)

They also sell a clamp-on style and lots of other interesting pieces for the do-it-yourself PHB fabricator :thumbsup:

Yeah I looked at the website but no infor is give on the width of the mounting channel.

jfman,

Give those places a call. They should have parts drawings to help you out.

As far as the axle mount, don't think you can just flip it to the other side. The axle location (left or right) has an impact on handling characteristics. Also, if you mount the bar high enough to have a horizontal bar, the roll center will be *very* high. You'll may also run into exhaust or floorpan clearance issues. That's why mine is currently diagonal...not an ideal situation, but a set of compromises.

Ryan

I would expect that the width of the mounting channel is set by the size of the rod ends used.

For example the Speedway mount specifies 3/4" holes so I might expect to use a heim joint with a similiar size hole... looks like the width of a joint this size is about .875" (7/8").

Might find this interesting: http://www.racerpartswholesale.com/pdfs/qa1cat.pdf

The information is out there... :-)

Yeah I looked at the website but no infor is give on the width of the mounting channel.

I have that mount on my car and a 3/4" heim joint just does fit in the channel. No room for washers or anything else. The channel measures 7/8"

I have that mount on my car and a 3/4" heim joint just does fit in the channel. No room for washers or anything else. The channel measures 7/8"


Thanks !

Just a thought but why do you need a panhard bar on stock 4 link?With urethane lower bushings and rubber uppers and wide tires~ 3/8" or less clearance between tire and wheelhouse lip I have had no tire rubbing even under hard cornering and getting sideways on a daily basis.I am also looking into a 3 link since so many people like the idea of them.Either that or the HTH truck arm kit.

Just a thought but why do you need a panhard bar on stock 4 link?With urethane lower bushings and rubber uppers and wide tires~ 3/8" or less clearance between tire and wheelhouse lip I have had no tire rubbing even under hard cornering and getting sideways on a daily basis.I am also looking into a 3 link since so many people like the idea of them.Either that or the HTH truck arm kit.
It's not a tire-rub issue, it's a Roll Center Height issue. The RCH with a C4L rear is way too high (height of the UCAs) When you add a PHB, the RCH drops to the height of the center of the PHB.

Roll center height is a big one...

But just as big is the positive lateral location of the axle provided by a PHB. I don't know about you but I can "rock" the car side to side and see the movement. Just watch the tire tread move back and forth as you do this and you *will* see movement. This movement results in a car that is a bit twitchy in the curves and requires constant small steering corrections. Eliminate this sideways movement and the car grooves with far fewer corrections to steering required.

Sometime I want to instrument the back end and find out just how much it moves around. I am thinking of a pencil attached to the rear end riding on a paper and clipboard attached to the body. Go drive around awhile. Should produce a big scribbly circle and show the limits of movement.

If/when I do this it will be with poly lowers, rubber uppers, a rear sway bar, and all stock arms. So almost a best case for the C4L rear suspension.

I don't have any lateral movement... I'm running rigid arms with solid rod-ends at all 8 points. I have about 1/8" of tire clearance, and have no rub problems at all... of course, with my current tires, I can't really push it as hard as I'd like, but I try anyway. :D

If I were to install a PHB, I would first put rubber in the uppers to allow some side-to-side movement to minimize some of the conflicting RCH issues of running both a C4L and a PHB.

I have no panhard bar either and see no rocking other than tire sidewall. I have GW lowers in the rear, stock uppers with moog bushings, hotchkis sway bar, and edelbrock trailing arm braces. Is there really a point to running a C4L and a PHB? I think the benefits would not be worth the fighting your suspension would go through.

On the street, with street tires you'd probably never notice an improvement. It might feel "different" but the butt-o-meter won't be able to tell that it's "better" ...unless you've got one of those elusive uber-sensative sport-compact butt-o-meters that can notice the car feeling faster when you add a wing and stickers. :D

On the track, you may notice slightly faster lap-times with a PROPERLY DESIGNED PHB setup with the RCH dialed in where it works best.

We are bordering on the edge of personal opinion and perception here as opposed to factual data...

I very much doubt the arms have anything to contribute here, I believe it is all in the bushings. With all solid links as Derek has, there really should not be any movement. YMMV but I do not consider solid links a practical street car solution due to NVH and the limited lifespan of the rod ends in this environment.

I know that, at least with all rubber bushings, I have seen sideways movement on my El Camino. I know that in full droop there is a significant side gap and distortion of the upper bushings. This leads me to believe that the RC conflict between PHB and C4L will not be an issue and the upper rubber bushings will allow all the movement needed.

I also know that on another C4L suspension I noted a substantial difference in feel when the lateral location was firmed up (albeit from a completely different suspension design). And I do not consider my personal butt-o-meter to be even close to uber-sensitive.

A PHB can lower the rear RC and thus reduce lateral weight transfer from weight jacking. Anything that reduces lateral weight transfer will improve cornering performance. The limitation is in balancing out the suspension. You have to maintain enough rear lateral weight transfer to match the front end.

The're a reason why all the new SRA muscle cars used a panhard bar. The new mustang and the 4th gen camaro have them from the factory.

Good post Steve! Provided there`s a lot more compliance in the upper arms than the PHB I think it`s fairly safe to assume that the PHB will take over the role of RC and lateral axle location. Our 3 link/PHB test car is a whole different car with that suspension in it. It`s really linear and predictable. Lots of fun to throw around and NO suprises. I`m sure a lot of that comes from the PHB. One of the issues with the C4L is that the RC moves all over the place and actually goes up as you lower the car making a bad situation worse. Even a fairly high mounted PHB could at least stabilize the RC. The closer you get it to the factory RC the less conflict there should be between them so it may actually be better to only drop it 2"-3". FWIW our adj. PHB can go as low as around 9" or as high as stock. We`ve tried it everywhere and the car works best with it higher than you`d think (14"-15") despite changing spring and swaybar rates all over the patch. Bear in mind we`ve also got totally revised front end geometry (G-5) so the roll axis inclination is altered a LOT anyway. The problem with changing things too far from stock is that none of the aftermarket springs,bars etc. will be even close to right anymore. A watts would probably be an even better choice than a PHB because it would keep the rear perfectly centered and have less RC conflict. Done well it would probably yield a noticable improvement. Mark SC&C

We are bordering on the edge of personal opinion and perception here as opposed to factual data...
I think we're both trying to say the same thing, just not quite on the same page... I had to way over-simplify what I wanted to say because of the extremely short ammount of internet-time I get while at work (as long as it takes my boss to have a smoke... if he gets a break, so do I. :yes: )

I very much doubt the arms have anything to contribute here, I believe it is all in the bushings. With all solid links as Derek has, there really should not be any movement. YMMV but I do not consider solid links a practical street car solution due to NVH and the limited lifespan of the rod ends in this environment.Those thin stamped steel arms do have a very limited ability to compress & stretch, but I will agree, most of it is in the bushings... I think some people get confused, and think there is a lot of side-load placed on the arms, but I'm not one of them. ;) As for NVH from rod ends, I disagree... the rear arms do not support the weight of the car, the springs do. Sure, there will be a little more (much like running solid in the front upper A-arms), but it's really not bad... Again, I agree with the wear issues, but to me, it is worth the performance benefit to have bind-free/resistance-free motion of the rear suspension. A rod end in an control arm is really no different than a rod-end on the PHB in those respects...

I know that, at least with all rubber bushings, I have seen sideways movement on my El Camino. I know that in full droop there is a significant side gap and distortion of the upper bushings. This leads me to believe that the RC conflict between PHB and C4L will not be an issue and the upper rubber bushings will allow all the movement needed.

I also know that on another C4L suspension I noted a substantial difference in feel when the lateral location was firmed up (albeit from a completely different suspension design). And I do not consider my personal butt-o-meter to be even close to uber-sensitive.

A PHB can lower the rear RC and thus reduce lateral weight transfer from weight jacking. Anything that reduces lateral weight transfer will improve cornering performance. The limitation is in balancing out the suspension. You have to maintain enough rear lateral weight transfer to match the front end.This I think is where we missed each other's points... you're right that you will definitely notice a difference in the way it feels by locating the rear laterally with a PHB, however, in a case like my setup, I've already located it with the use of rod ends. Where I disagree, is that I have a hard time believing that the change in RCH will yield results that the average driver with a street car, on street tires, on public streets is going to notice a big improvement from a well-balanced car with a high RCH vs. a well-balanced car with a more favorable RCH. If we're talking race-cars, or even occasional track cars, yes by all means do whatever can make it faster... for the street, IMHO, it's not really worth the effort. What I think is adding to the confusion, is that while we're both talking theory, and such, we have a few posting questions who may not have as great of understanding of the purpose/benefits/etc. of the PHB, which is where my simplified answers were aimed. :)

The're a reason why all the new SRA muscle cars used a panhard bar. The new mustang and the 4th gen camaro have them from the factory.That's because the C4L isn't that great of a design (not terrible either, but there's better out there) and in the case of those cars, with 3-links and torque-arm setups, a PHB or watts link is REQUIRED to locate the axle laterally. Our design already has lateral location designed into it, so it's not required - but we can still benefit from sticking one in there, if designed properly.

Our 3 link/PHB test car is a whole different car with that suspension in it. It`s really linear and predictable. Lots of fun to throw around and NO suprises.How much different does it feel from a well balanced car with C4L?

We`ve tried it everywhere and the car works best with it higher than you`d think (14"-15") despite changing spring and swaybar rates all over the patch.I would have expected it to work best in the ~10" range. What negative effects did you experence by going that low? Just not enough roll stiffness?

The problem with changing things too far from stock is that none of the aftermarket springs,bars etc. will be even close to right anymore. This is partly why I'd have a hard time suggesting going with a PHB on a forum like this... you just don't know the experience level of the person reading, and taking your advice. I sometimes cringe when I see someone mention they're going to try to design something for their suspension, when you can tell they don't really have a working knowledge of the function and side-effects of it. You probably do the same when you see me offer advice :D ;)

Wow Derek, quote much? ;-)

Side load on arms? We are on the same page, it's all about the triangles. And Marketing :-)

On the issues of NVH and wear, this is exactly what I was getting at about edge of perception and opinion. What you consider acceptable I consider bothersome and that should be understood/noted rather than argued. I noted a lot more "clunk" when I replaced the rubber strut mounts on my Mustang with solid links (I was going for adjustability) and thus have personally ruled out solid links for future street use. When I think about PHBs I wonder about the adaptability of late Camaro parts. I have noted that speedway carries a poly rod end that could be a very interesting piece though.

The issue that Marcus ran into with the rear RC height was the reduction in lateral weight transfer due to jacking. The low RC reduced lateral weight transfer so much in the rear that they were unable to balance the car with springs and anti-roll bars. Thus the performance suffered from excessive understeer.

What I learned or took away from Marcus prior description of his experience was that most of us grossly underestimate the affects of weight transfer due to jacking. After all you cannot see it, you cannot feel it, but it is definitely there.

I might argue with Marcus that the aftermarket springs at least are still just as close to right as they ever were. I tend to select springs based on ride quality or natural frequency rather than attitude control. Since the suspended weights are still the same, the natural frequency with the aftermarket springs will also still be the same. Irregardless of RC heights.

Now anti-roll bars, that is a different story and personally I think all of the bars which bolt to the rear LCAs are of much lower value. Which pretty much rules out most of the aftermarket.

I might agree that most could not tell the difference between a car that corners at .80G and one that can hit .90G on the street. But reducing RC height could have that type of affect, although I have no idea what the actual degree is. I am confident that just about anybody could tell the difference, on the street, with positive lateral location of the axle though.

On the issues of NVH and wear, this is exactly what I was getting at about edge of perception and opinion. What you consider acceptable I consider bothersome and that should be understood/noted rather than argued. I noted a lot more "clunk" when I replaced the rubber strut mounts on my Mustang with solid links (I was going for adjustability) and thus have personally ruled out solid links for future street use. Sounds like those solid links are in a place where the weight of the car is loaded on them, which will typically give you a very noticeable increase in NVH. The rear links of the Chevelle chassis only locate the axle, the weight of the car rests on the springs - that is where most NVH is transmitted.

The issue that Marcus ran into with the rear RC height was the reduction in lateral weight transfer due to jacking. The low RC reduced lateral weight transfer so much in the rear that they were unable to balance the car with springs and anti-roll bars. Thus the performance suffered from excessive understeer.
I understand what you're saying, but I think you're saying it backwards... a higher RC reduces weight transfer (roll) due to jacking. Lower RC increases roll because jacking is reduced.

I think this would be way easier, and much more fun to discuss if we were in the same room, and had a pencil & paper handy... some of this stuff is kind of hard to put into words.

This is good stuff. :) It`s hard to describe how the 3link/phb works vs. the C4L. It`s not so much a matter of ultimate grip,although that`s improved also. It`s how linear and predictable the car feels. With the C4L when you pushed it really hard (I`m talking the very ragged here) the "limit" in the rear was in constant flux and you had to constantly adjust for it. Every road imperfection threw you a new and often unpredictable challenge (non linear binding and deflection anyone?). When you stepped past the "limit" things got real interesting real fast! Unnerving at 90mph. More than a few A and G body have met their maker this way I`m sure. The G-5 front end on the other hand was/is very linear and planted and asking "Is that all ya got?". It`s almost like driving 2 different cars..at the same time. With the 3 link/PHB the rear just follows the lead of the front. The car`s planted,the "limit" is easily felt and if you step past it the car reminds you that you might want to step back a bit please. If it were easier I`d pull the 3rd link out and put a set of stock upper arms back on to see how much of that`s the PHB. That car doesn`t have a stock crossmember in it anymore though. I may have to experiment some with our Stage2 equipped Monte and a watts or phb. I`m curious.
The reason we had to add more rear spring is that at the kind of rear bar rates we were running it would start to tripod or pull the inner rear wheel off the ground in hard cornering. Dropping the bar rate down (we`re still running more than 4X the rate of a stock bar) and going to 200lb/in rear springs kept both rear tires loaded much better and produced a better feel as well. Again,why we do so much real world testing. I originally predicted that a lower rear RC and much lower bar and spring rates would yield the best package. The performance of 3rd and 4th Gen F bodys would seem to bear that out. However the car disagreed with me and was thoroughly unimpressed with my opinions. So we adapt and we learn.
Our original system had Aurora`s best teflon lined heims in the 3rd link and phb. YMMV but within 5000 miles there was an audible buzz coming from them at highway speed. In 10,000 miles they were buzzling enough that you could feel it in the steering wheel and it would give me a headache. By around 13,000 you could hear them "clink" at idle when driving slowly accross a parking lot. Caveat: This car was driven rain or shine and has a full cage which may help transmit NVH. We built all new brackets and replaced them with Currie Johnny joints. Nice and quiet now. It`s not a weight issue,it`s a wear issue. I`ve seen/heard similar things with countless drag cars and street rods in our hot rod shop over the years. We have drawers full of heims that were noisy but otherwise okay and we couldn`t bear to just throw them away. We use them for 4wd off road stuff. Others may have had better luck with them but my rule of thumb for cars is that I`d rather not use heims unless the car has open headers. I`ll make exceptions for cars that are hardly ever driven and swaybar end links. Mark SC&C

Sounds like those solid links are in a place where the weight of the car is loaded on them, which will typically give you a very noticeable increase in NVH. The rear links of the Chevelle chassis only locate the axle, the weight of the car rests on the springs - that is where most NVH is transmitted.
No actually the solid links are the top of a strut, so you can think of it as the end of a shock and a suspension link point.
I understand what you're saying, but I think you're saying it backwards... a higher RC reduces weight transfer (roll) due to jacking. Lower RC increases roll because jacking is reduced.
I may have confused things here by calling it "jacking". To try and get to a common vantage point... First all weight transfer results from the leverage between CG and ground. Next this transfer is broken into two components by the RC. The first part of the weight transfer works through the leverage between CG and roll center to cause body roll (important to note body roll is an effect not a cause). The second part of the weight transfer works through the leverage between RC and tire contact or ground and is what I was calling "jacking". We see and feel the first part but not the second part of the weight transfer. I have been mistaken in thinking that reducing the second part of the transfer would reduce the overall transfer, but it turns out it does not. It just reapportions the transfer with more going into the CG--RC component, resulting in more body roll as we all expect.

I think this would be way easier, and much more fun to discuss if we were in the same room, and had a pencil & paper handy... some of this stuff is kind of hard to put into words.
Yep, a few napkins and a cold beverage would help :beers:
I good book or two helps as well because they often explain it much better than I do. Plus they get to use pictures :thumbsup:

Marcus, your descriptions of linear and predictable behaviour match up very well with my experience of the difference between the C4L setup in my Mustang and the IRS in the same car. I have one particular benchmark corner which I drive on the way to work. This is basically a long freeway offramp which, without impeding traffic, can be taken at 85 MPH and a :D . After the conversion I would say the steering corrections are 80% less than before. You just setup the turn and it stays there. I have also noted that it is easier to catch and correct tail slides but was never sure of what to attribute that to (too many variables). I personally believe most of this is due to the improved lateral location of the rear suspension.

I have one particular benchmark corner which I drive on the way to work. This is basically a long freeway offramp which, without impeding traffic, can be taken at 85 MPH and a :D.

Likewise, we have a S on ramp, it is banked perfectly, and you can take it as hard as your car will let you. Let's just say 70 in a '01 Suburban is pretty sweet. :eek:

I guess I'll have to draw up a diagram tonight when I get home... I know exactly what you're saying now... you and I were thinking about the same things, just describing it differently, and focusing on different parts of it... :clonk:

Yep, a few napkins and a cold beverage would help :beers:
I good book or two helps as well because they often explain it much better than I do. Plus they get to use pictures :thumbsup:

I can go one step better than a napkin... AutoCAD :D

Here we go... This is the effect lowering the RCH has on roll stiffness.

http://www.chevelles.com/showroom/data/516/medium/ROLL_CENTER1.jpg

...and here is the jacking effect you were talking about...

http://www.chevelles.com/showroom/data/516/medium/ROLL_CENTER2.jpg

Here is what confused me on what you were saying:
The low RC reduced lateral weight transfer so much in the rear that they were unable to balance the car with springs and anti-roll bars. Thus the performance suffered from excessive understeer.The balance issue comes more from the excessive roll (front end has to try to do all of the "roll stiffness" work) not the reduced jacking.

Anything I missed? :)

Nope, I think we are officially on the same page :thumbsup:

Now I am going to have to ponder on this a bit. That statement arose from an earlier discussion where I made a guess that Marcus saw a lot of understeer from the lowered rear RC. My guess turned out to be right... the problem is that I may have been using a false assumption when I made the guess.

So keep your AutoCad warmed up because this might get even more technical when I get back :D

My guess turned out to be right... the problem is that I may have been using a false assumption when I made the guess.Well, if you think about it, both of the above situations are happening at the same time... adding the PHB reduces rear roll stiffness (worsens front grip, by putting more load on the outside front tire) and at the same time, reduces jacking (improves rear grip by keeping more of the weight on the inside rear tire), so we're both right, and the balance is screwed up through both types of weight transfer. :)

More rear grip + worse front grip = dramatic understeer.

So keep your AutoCad warmed up because this might get even more technical when I get back :DI'll leave the AutoCAD on, but I'm turning my brain off. ;)

Why the heck did you use a 69 for the drawing? It should for sure be a 68, everyone knows they handle better anyway.

Why the heck did you use a 69 for the drawing? It should for sure be a 68, everyone knows they handle better anyway.Oh contraire, a stock '69 equipped with the optional F41 package, could handle better than any stock '68, as the F41 equipment was not available before the '69 model year. :boxing:

This was a fun discussion... what's our next topic? Swing arm lengths? Anti-squat? :)

Would you say the wheel base of an el camino is advantageous over a chevelle? Also, do you think the el camino needs a boxed frame as much as a convertible does? Even with the open bed, alot of steel there, is a boxed frame quite necessary on a elky, especially if your not hauling?

Brett, since the el camino doesn't have the full roof of a coupe or wagon, it does need the boxed frame for more support, much like a convertible does. Of course pickups don't (usually) have boxed frames, but the bed and cab are separate pieces. I guess that allows for movement which would be destructive to an el camino body.

The wheelbase is a mixed bag. On one hand the extended length of the El Camino does put a bit more of the weight on the back wheels percentage-wise as compared to a Chevelle. Further the extended wheelbase and length increase the "polar moment" of inertia. This means more of the weight is carried further away from the CG. This can help to stabilize the car and make it slower to spin. This is good.

Unfortunately that polar moment also makes the car slower to turn and once turning/spinning, a lot slower to stop.

And now back to the serious head thumping TECH :thumbsup: (ironic in a thread titled "basics") Forget the AutoCad and warm up the trig functions in your favorite spreadsheet. (Note: It took me awhile to get back to this because I was actually *working* on the project car rather than talking about it. Imagine.)

First the basic background theory...

A car is made up of sprung and unsprung components. For a car in a turn each of these components is subject to centrifugal force (CF), and this force works through the respective CGs of the components. Since the unsprung component weight is a relatively small portion of the total car weight, I am going to ignore it and focus on the sprung component.

The centrifugal force of a car in a turn works through the CG. Further this force creates a rotational torque that is proportional to weight of the car X distance between CG and ground. This torque creates lateral weight transfer. Note there is no mention of roll centers (RC) nor roll stiffness here as these do not change the *overall* lateral weight transfer, it is caused strictly by the interaction of force, weight, and CG height. Thus it is only changed by changing one of these parameters.

The overall weight transfer of the sprung portion is further divided by the roll axis. The roll axis is the line connecting the front and rear RCs and is A) where the body pivots as it rolls in a turn and B) where the sprung weight transfers into the unsprung portion of the car. The roll axis creates two torque moments: one for the CG-->RC and another for RC-->ground. Note that the total weight transfer caused by both of these torque moments will still equal the total overall sprung weight transfer but moving the RC up/down will change the proportion between the two.

The torque moment of the RC-->ground is resisted by the tire on the ground so there is very little movement involved. We cannot see nor feel this weight transfer except in it affects on tire grip.

The torque moment of the CG-->RC does create noticeable and visual effects in the form of body roll. This torque moment is resisted by the springs and anti-roll bars. Because we can change springs and anti-roll bars we can tune this transfer and proportion it between front and rear as needed to tune the cars cornering response. It is possible to create a suspension with NO roll stiffness such that all of the CG-->RC portion of the lateral weight transfer occurs at one end of the car.

And finally the reason why we get so excited about lateral weight transfer has to do with how tires behave when weight is added or subrtacted from the loading. As weight is added a tires traction/grip increases, but NOT as fast as it decreases when weight is removed. Since lateral weight *transfer* puts the same overall weight on the tires, one tire is decreased the same amount as the other is increased. The decrease loses more traction/grip than the increase gains so overall traction/grip is reduced.

And now to try and show why lowering the rear RC via a PHB create substantial understeer...

So it is easy to see that lowering the rear RC would lower the roll axis and thus reduce the RC-->ground torque moment. Which reduces this form of weight transfer. And since overall weight transfer is unaffected by roll axis that means that weight transfer from CG-->RC must increase. Which means we will see more body roll with no other changes. But if we see understeer increase it must mean more of the weight transfer is occurring in the front. Which means there must be a lot more roll stiffness in the front than the rear or we have excessive body roll creating bad geometry in the front suspension.

So what kind of roll stiffness do we have in the front? Well with a 61" average wheel track we get a 0.53" displacement of the body for every degree of roll, one side raises this amount and the other drops. To accomplish this the LCA will move through 1.6* of rotation. At the spring pocket that 1.6* works out to 0.30". That in turn equates to 117 lbs using the 390 lb/in spring on a '68 BB w/F40 suspension (the stiffest spring the factory used). But this might be more useful in wheel rate terms, so applying a motion ratio of .5 we end up with 29 lbs per degree of body roll. Hmmm. That does seem pretty low but that is just for the spring, and we know the factory used very soft springs and we see a lot more than 1* of body roll, so maybe that is correct.

We also have an extra spring in the form of the anti-roll bar. It hooks up to the LCA 16" out from the pivot, so it will see 0.44" of movement per side. The torsion portion of the spring works through a 14" arm which will rotate 1.8* to achieve that amount of movement. Now with a torsion bar spring rate we could calculate a spring force (note that the spring works through a 14" lever arm) and apply it's motion ratio of 0.73 to convert to a wheel rate. Then add it to the spring number and get a total. Trivial :D

How about roll stiffness in the rear? Well for each degree of body roll the axle will move 0.53" and with the springs set back at 18" from center, the spring will move 0.32" per degree. This works out to 51 lbs using a 160 lb/in spring (again '68 BB w/F40). But, and this is the tricky part, we have to apply the motion ratio (think lateral, thus rear view, of spring mounting) of 0.58 so the wheel rate is 17 lbs. Just over half what we have in the front.

What about that potential factory rear anti-roll bar? Well those LCAs rotate 1.38* so the ends can move 0.53". Again with a torsion bar spring rate we could calculate a real rate here. But also remember that the torsion bar works through 22" long arms back there which further reduce it's effectiveness. Compared with the front bar the rear has 20% greater motion but 57% longer arms to work through, I figure it is derated about 25% for the same torsion spring rate.

So if the RC was the same height front and rear you would need one really large rear anti-roll bar to rebalance things out. Largely because the rear spring configuration is not good for control of lateral weight. I would note here that another very common/popular C4L rear suspension placed the springs part way up the LCAs. This would reduce their regular fore/aft motion ratio such that it could match the lateral motion ratio. The net affect would be to allow higher spring rates and thus higher rear end weight transfer due to spring rate.

Anybody want to try some coil overs on the arm of their Chevelle along with a low PHB and see how close my analysis is?

Or alternatively have I missed or gotten something horribly wrong here?

Wow... I thought I would get at least some response...

I thought the notion of lateral motion ratio might stir some thought. But I guess I should have expected it to go quiet after Derek said he was turning his brain off ;-)

Steve,

I'd jump in but my job is slowly turning my mind into mush. I'll try to respond intelligently soon. You guys are doing a good job so far :thumbsup:
Ryan

I think you`re heading in the right direction. I`m also glad that someone here has longer posts than I do. ;) Personally I don`t think the spring on the lower arms approach (ala Fox Mustang and vintage Impala) is the way to go. It just opens up a whole new kettle of fish with bushing loading and possibly increased binding. In near stock form those cars exhibit some really evil handling quirks. Note that Fox Mustangs are often (usually?) converted to coilovers and a 3 link or torque arm setup with PHB in classes that allow it. The newest version also goes to mounting the springs to the top of the axle tubes (and a 3 link/PHB). I think there may be a lesson there. I think most Chevelle owners would be very happy indeed if they could hang in there with a new GT-500 Stang in the twisties...and toast it on the straights! :thumbsup: By all accounts those cars work quite well in spite of their stubby little 3rd link. They are running what looks to be about an 11" rear RC height though. I wonder what kind of rear spring rates they`re running? Mark SC&C

But I guess I should have expected it to go quiet after Derek said he was turning his brain off ;-)I'm still not ready to turn it on yet either. ;)

I'm still not ready to turn it on yet either. ;)
What, too busy smacking folks for over using their credit card? :p

'Now go away before I taunt you a second time' :beers: (sorry my kids have Monty on the brain and I am afraid it is contagious)

Marcus, when you have real information it usually takes more words to convey. Yeah the Mustangs do have poor handling in the rear in stock form, but I think they have much bigger problems working against them than the spring location and LCA bushing loading. And aren't coil overs mostly bling in many applications (with the notable exception of the front of Fox Mustangs)?

The binding is a good counter point though, although it would still be less than what you see in the front LCA. Leads me to think it could be manageable. But all in all it is probably more effective to work the anti-roll bar instead for roll stiffness.

It would be very interesting to take a set of wheel scales and spend a day putting some empirical data together. Little things like see how a 2" wheel height offset changes wheel loading. Would put some real world numbers on roll stiffness. Now if I only had wheel scales... they are just a bit expensive to play with on such a limited basis.

OK Steve, I'm finally ready to think about this... :clonk: :beers:
I agree with all of the first part, which describes much of what I tried to convey with my drawings. :thumbsup:
...But if we see understeer increase it must mean more of the weight transfer is occurring in the front. Which means there must be a lot more roll stiffness in the front than the rear or we have excessive body roll creating bad geometry in the front suspension...
I'm going to go with the roll-stiffness as being the primary cause here. The front isn't getting any help from the rear to resist the weight transfer (roll stiffness) so more of the load is placed on the outside front tire, and taken off the inside front tire. In the rear, it leaves more of the weight on the inside, and transfers less weight to the outside tire. Rear traction is increased, and front traction is decreased.

...Largely because the rear spring configuration is not good for control of lateral weight. I would note here that another very common/popular C4L rear suspension placed the springs part way up the LCAs. This would reduce their regular fore/aft motion ratio such that it could match the lateral motion ratio. The net affect would be to allow higher spring rates and thus higher rear end weight transfer due to spring rate.
I disagree with this... You essentially make the LCA into a lever, so for instance, if the spring (same rate in this example) were moved to 7/10ths the way back on the LCA, it would do exactly 70% of what it did before, as it is only controlling the up & down movement of the LCA. Rather than moving the springs to the LCA, I would suggest moving them further outboard on the axle. This will increase their effectiveness for roll resistance, without changing the wheel rate.

can i throw a wrench into this?What would happen if some one would run the lower links parrelle so you would not have the lower arms converging like the top c/a's.I know this is off camber for this link but derick suggested it to me...........maybe it is time just to sit quietly in the corner.

OK Steve, I'm finally ready to think about this... :clonk: :beers:
Welcome back :)
...I'm going to go with the roll-stiffness as being the primary cause here. The front isn't getting any help from the rear to resist the weight transfer (roll stiffness) so more of the load is placed on the outside front tire, and taken off the inside front tire. In the rear, it leaves more of the weight on the inside, and transfers less weight to the outside tire. Rear traction is increased, and front traction is decreased.
With some of the aftermarket spindles or the scandc stage 2 setup I would tend to agree. What I was thinking and getting at there was that the factory geometry is so bad at keeping the tire vertical that body roll just makes it that much worse.
I disagree with this... You essentially make the LCA into a lever, so for instance, if the spring (same rate in this example) were moved to 7/10ths the way back on the LCA, it would do exactly 70% of what it did before, as it is only controlling the up & down movement of the LCA. Rather than moving the springs to the LCA, I would suggest moving them further outboard on the axle. This will increase their effectiveness for roll resistance, without changing the wheel rate.
I think you missed one of my points and went a different direction on another...

First moving the springs up onto the LCAs could effectively move the spring force laterally outbound. Note that the LCAs mount farther out the axle than do the springs. This would have the benefit of increasing the lateral motion ratio. Secondly, even if that were not the case, moving the springs would decrease the normal motion ratio as you noted. This could make the fore/aft and lateral motion ratios match. So I presume a change to stiffer springs to compensate for the fore/aft motion ratio change and provide the same wheel rate. Thus roll stiffness would be increased without any change to natural frequency or suspension ride quality.

Barnfresh, changing the angle of the LCAs would not have much of an affect as the convergence angle is relatively minor. The real lateral location of the axle is provided by the triangle of the UCAs.

Thanks for clarifing that.I was a little confused as if it was a big deal or not.

Of course the reason the factory probably put the springs on the lower arms rather than the top of the axle tubes is that it let them use a nice tall spring and still lower the trunk floor about 3" to give the car more interior room. :thumbsup: I`m pretty sure the car`s engineers never had a conversation like this (although they should have!). :yes: Mark SC&C

OK Steve, I follow what you're saying now. :clonk: Interesting idea, something I've never considered, but wouldn't you add the motion ratio of the arm, to both the fore/aft, and lateral ratios? You wouldn't get any closer, as you'd add the same ammount to both. It wouldn't have any different effect than moving the spring outboard to right above the LCA mount, would be a lot more work, and place more the load entirely on your bushings.

I`m pretty sure the car`s engineers never had a conversation like this (although they should have!).If they did, you'd be out of business. :o Be careful what you wish for. :D

I think you are probably right Derek. I wonder how far outside we can get... hmmm maybe those coil overs *would* be a good idea :-)

With some adequate bracing, you could move the spring to be just inside of the outer part of the frame rail. Any wider would get into the wheel-well, and start limiting tire sizes.

Without actually looking, I'd guess they could be moved ~4" outward.

Actually the main part that needs to be moved out is the lower mounting point. The lower shock mount is pretty far out there already. Actually taking a look it is *outside* the LCA mount and about 8" outside the OEM spring perch centerline. Thus my reference to the coil over.

This would take it from a lateral motion ratio of .58 to .84. A notable improvement.

Rosie 67' ElCo
C4L+PH, drop down brackets, air bag, no sway bar cause Edelbrock lowers are tarded, and GC that is way too high cause I can't pick a nice spring. Picture is shown in full droop.

I can't tell if this handles great or good cause the front suspension unalignable with current hardware. Arrrr! Mark I think happy AFX thoughts when I buy that once a month lottery ticket.
http://myspace-076.vo.llnwd.net/00785/67/00/785100076_l.jpg


J5 96' Impala
C4L+PH, drop down brackets, metco, fatty Herb Adams rear bar, stock springs, air bag. Picture is shown in full droop.

This car handles like nothing else I have driven, beats just about anything with a license plate at the auto cross @ 4300 pounds 275s
http://members.aol.com/tunedbytad/images/bar_IC_brackets.jpg

I'm not as technical as Mark, Derek, vroom or Dennis but going out to Chewy72SS the panhard rod works!


Here's what I know:
- The longer the bar, the better.
- Bar should sit about level at static ride height, with half tank of gas.
- One frame mount, one rear end. (Both double shear.)


I mounted my bars as low as possible flush with the bottom of the diff.
Loaded I have my bars very close to level. The axle wont move much I have no rub marks on the ElCo and it has 295/45/18's out back
Single shear works if you make the hardware BIG. Double would be nice.

I first put a pan hard bar on the Impala to keep the trunk from whipping back to center when exiting turns. It was like a 21 gallon slide hammer when the fuel hit the other side of the tank. The panhard ended the trunk whip and fuel slidehammer!

To my surprise the panhard ended my wheel hop when launching the Impala at the drags. So when the Edelbrock 4link did not end wheel hop on the ElCo (420 RWTQ Powerglide) I added a Panhard and all wheel hop evaporated!

Rosie 67' ElCo
C4L+PH, drop down brackets, air bag, no sway bar cause Edelbrock lowers are tarded, and GC that is way too high cause I can't pick a nice spring. Picture is shown in full droop.

I can't tell if this handles great or good cause the front suspension unalignable with current hardware. Arrrr! Mark I think happy AFX thoughts when I buy that once a month lottery ticket.
http://myspace-076.vo.llnwd.net/00785/67/00/785100076_l.jpg

One thing I'd like to comment on, is that your adjustment is located near the center of the bar, where buckling loads are highest. This probably won't be much of a problem for a street-car, but you may have trouble with this with sticky tires. The adjustment sleeve should be located as far to the one end or the other as possible.

J5 96' Impala
C4L+PH, drop down brackets, metco, fatty Herb Adams rear bar, stock springs, air bag. Picture is shown in full droop.

This car handles like nothing else I have driven, beats just about anything with a license plate at the auto cross @ 4300 pounds 275s
http://members.aol.com/tunedbytad/images/bar_IC_brackets.jpg

This PHB looks better. :)

I see on both cars, you have the LCA mounts located lower for increased A/S. Do you run them like this on the autocross track? Do you experience any brake-hop with the short SVSA?

One thing I'd like to comment on, is that your adjustment is located near the center of the bar, where buckling loads are highest. This probably won't be much of a problem for a street-car, but you may have trouble with this with sticky tires. The adjustment sleeve should be located as far to the one end or the other as possible.

This bar is only temporary on the ElCo. The 8.2" rear end has been wasted since before I was born. Then I had to go put a new 383 in the car now the ring an pinion is mush. A stouter better designed bar will happen when the 12 bolt goes in. The ElCo is not going to be ready for any serious action for a while.

Do you run them like this on the autocross track? Do you experience any brake-hop with the short SVSA?

I actually do run the Impala @ the autocross with the arms set on high A/S. I really need the help to bite when leaving the corners. W/O them I do a 2nd gear rolling burn out like an "elephant on roller skates™".

To get the rear wheels to hop or break loose while braking, I have to manually down shift while on the brakes while having some kind of steering going on.