I'm planning a traditionally styled FED T-bucket for the street. In so doing, I've looked at quite a few front end suspension designs. This is a design that incorporates several ideas from several places. I wanted to run it past the experts before putting a bunch of money and work into a bad idea. What do you think? The advantages are: 1. Simple: It's a 3 link. 2. Uncluttered: No shocks or shock mounts or air bags, etc. 3. You can adjust the ride stiffness (up & down) independently from the sway (lean in corners) independently from the bounce (shock absorbers) independently from the ride height. Most suspensions are a compromise between all these. If you change one, it affects the others. This one is independently adjustable. 4. Traditional: Well, that may be a stretch in some of your opinions, but on a FED, I'm allowing myself a little more latitude than if it were a 'duce or an 'A. They tried all kinds of crazy ideas all the way back to the '50's on dragsters. 5. Light weight (for a solid axle.) Has anyone tried anything like this? How'd it work? Can anyone shoot holes in the theory? EDIT: The second picture is an updated design, thanks to everyone from posts 2-41. It eliminates the weight and complexity of the sway bar by using the torsional stiffness of Henry's axle. See post # 42, page 3 for further explanation. 12-8-08 Edit#2: The third picture is from fellow HAMBer "64Dodge440." The fourth and fifth are from John Ewald at the 2007 CHRR at Famoso. Glad to know I'm not the only one with this nutty idea.
Hmmm... not sure? My first thought is that it will allow the axle to rock very freely because the spring won't offer much resistence in torsion i.e. when one side hits a bump, or in cornering there's not much resistence to body roll. Also, will the arms have the ability to twist? Obviously you can't bush them at the chassis because that is where your friction material is and so those friction faces will need to stay in contact (parallel) while the axle rocks. My appraisal is by no means expert or scientific. That's just what I see. I like the thinking though....and the simplicity. Pete
Going to need a pretty big sway bar, since the spring creates zero roll stiffness. And you probably still need shocks.
I agree with the other comments/ It is simple, but offers no roll resistance nor dampning.. I suspect you willl need to run shocks to get any kind of a decent ride out of it.
How far are you intending to push the axle out past the spring mount? I ask because the further out you get, the higher all the suspension loads will be. You'll have to run some kind of dampener to keep it from wobbling all over the place. This is just theory at this point, but judging by the drawing, I think it's too flimsy and unstable for something you want to put a lot of power to and drive fast. I think I would look to actual, competitive drag cars (from the era) for further inspiration. What about a torsion bar?
Wouldn't you get some twist in the spring??? Maybe not much, but enough to fracture the spring eventually? Don't claim to be an expert, just a thought. I would be interested to see if it works out though.
I agree with gotgas, there isn't enough lateral support in the suspension with everything that far out. As far as being able to adjust roll stiffness independently of ride stiffness I'm not sure what you mean? or maybe how you intend to do it, I'm a bit confused with that one? Not to mention ride quality as far as a suspension damper goes is usually more of a high frequency control, whereas roll and pitch are very low frequency damper controls. Any sort of friction damper is extremely digressive in it's ability to handle any high frequency inputs, not to mention, a friction damper is going to offer the same resistance in both compression and rebound, which is way less than ideal and why they went away for the most part on road going vehicles so long ago.
I know here we go again but I cant help it. Ive been around a long time. I have it on my senior dragster. I am going to the shop now to get you a photo. hang on. You still need shocks though. I put mine on a 45 degree angle to give control in both planes. Bottom link in centre is a 1/4 eliptic spring made from a 69 Dodge Dart rear spring. It is quite short but works about perfect for this car and its weight. Car handles very very well. in fact if you watch the video from my website you will see it goes very straight. Suspension still works as can be seen in both the video around the yard and the last race video. It drives like a normal car with no bad habits. Tis a long story how I got to do this design but I will save that unless someone actually wishes to know. So anyway yes it works and it works well. You can blow these photos up for a better view. Don
Don, I can see the front end of your car working based on the fact that you're not putting big lateral loads on the suspension, and like you said, the distance from your axle to the pivot is very short. wsdad is building this for a street car which will see much more cornering and braking loads, not to mention all the other things a street car would see above and beyond what a drag car would see. Not trying to discredit you at all don, I think your setup works fine for what you use it for.
do a triangulated bottom link ...like a wishbone...with 2 links on the top of the axle ....there have been a few hot rod 32's out lately with this style setup.....
I always consider a 3 link a poor excuse for a 4 link. Those arms look kinder long and I dont believe 1/4 eliptic springs ever worked all that well as suspension members. You will need some side ways or triangulated bracing to steady things. By all means try it but dont go killing or injuring yourself or anybody else for that matter. I also like your thinking but I have serious reservations.
What about just running the two outside links and using a bell crank type set up on the chassis end with coilover that you could hide.? Rough pic with coilover in red.
I think that it is easier to describe this as a 3 point suspension. Will it work yes to a point but practical???? Your drawings give a good idea with what you are doing but they are only two dimensional. You have a top view, a bottom view and a side view. Both the top and bottom are the same plane. What you forgot was an end view. There are basically 6 parameters to deal with in suspension design. Horizontal, lateral, vertical and the rotation around each of these as an axis, roll, yaw and pitch, yes just like an airplane. If you are designing for the street you should be thinking about a minimum of 3" up and down travel to compensate for the road surface. I didn't want to get carried away but it appears that you are designing for a street operated machine, unless you live where the roads age glass smooth you have a problem. Here are some issues that I spotted with out getting picky so here are a few. 1. Excessive caster gain and loss during travel due to short arm length. 2. Unless you have adjustable ends on the sway bars there is no way to square chassis to axle,meaning measurements must be exact. 3. Lack of shock dampening, must have shock absorbers. 4. Excessive bind during roll cornering as the arcs of the sway bar react with the torsional twist of the spring. Since you are good with your computer redraw this from the end view and side view and then run it thru a couple scenarios of compression and drop with both wheels and then each side. What you need to do is measure the swing and rotation of the axle to its center line and its relationship to the swing and rotation to the relationship of the center lines of the suspension components. By plotting this out and measuring the distance change you will see how successful your idea is. Hint you shouldn't be able to read it with a 1/16" graduated tape measure.
how do you get any camber change on a straight axle? did you mean caster? The only way the camber would change (angle of the hub face to the level surface of the road) is if the front wheels are coming off the ground, at that point I think there'd be bigger problems! I don't think there will be much caster change with a setup like that seeing as the 1/4 eliptical spring is mounted on essentially what appears to be the same fulcrum point as the sway bar.
A couple of things from someone who has done it. First it no more is unstable sideways than a rear end is sitting on a leaf spring. the spring eye positions it and the spring cannot move sideways. The ends do not need to be adjustable. The arcs need to be preplotted. Some caster change on braking is ok. Anti dive or whatever you want to call it depending on where you were born I guess. Principle though is the same. 1/4 eliptics ? Have been around for years although maybe not so much here in NA. A spring is a spring is a spring. Inches deflection per pounds force is what matters. Would I do a three link for a street car. No #1 because there is no reason to. would I do a four link using 2 1/4 eliptics for the bottom links for the street? In a heartbeat. In fact I am building exactly that setup into the hemi jeep project. I know it is a race car but it would be streetable just fine. I dont know how you got to thinking about 3 links but I am pleased you at least considered it and give you credit for exploring the idea. Here is how I got there. I was visiting a shop owned by some old top fueler guys. I had been friends with them since i was a teenager. (40 years ago) They were this time (about 2 years ago)working on a nostalgia front engine fueler and were making the front end set up. It consisted of two flat plates sandwiching 5 hemi valve springs and was held together with 3/8 bolts through each spring and a castlated nut with cotter key securing each bolt. There were also the traditional two top links out to the outer ends of the straight axle. It was despite having 5 vavlve springs essentually a three link set up. Now I have known these guys for years. They are good builders and such but they are NOT inovators. They would always do what someone else had done first so I know without asking they saw someone else using this and knew it would work. Me myself I had always been fascinatedby 1/4 eliptic springs ever since I saw KS Pitman use them in his 33 Willys gasser. Since I made my living as a mechanic I also had studied suspension in detail during my training and during my years as an instructor as well. I saw an oppourtunity to try the 3 link and use a leaf spring 1/4 eliptic in place of the 5 valve springs and so i did, well aware that no one would probably understand the design and fully prepared to scrap it and go with plan B should it give any sign of unpredictabilty. Surpisingly it did not. A friend who is an experienced altered pilot helped me back the car up after the burn out asked me ""Man that car seems to go really straight. What is it like to drive'?"" I replied ""I think I could put my finger in my ear and it would still go straight."" i do not have to correct it at all even for the whole 1/4 mile. I am not advicating it as a better system so dont take this as a recommend but does it work ? Yes, and very well in this race car design. What I like about it is for a race car with a hard tail (solid mounted rear end) it does not in anyway fight the rear end and its abilty to plant the tires since its load point or pivot point is central to the front of the car. Same reason we make frame rails narrow at the front and radius arms from the torsion bars closer together than they need be if ride was our only motivation. I like to explore ideas , especially now that I am retired but I am also safety conscious. For a light weight race car it is a practical system with not a lot of unecessary weight. For a street car i would say a definate no. Or put a better way. If I was building a street car i would use a 4 link of some description. BUT and it is a big word. many of the ills one might think would be there just turned out not to be so in practice. I have by the way just for the record driven it around the front field on the farm here and the front end did work wonderfuly well even on the bumps. The solid rear though played hell with my poor old back and bum. So dont stop thinking about ways of doing things but remember everything has its place and limits. Different isnt always better. Sometimes it is just different. Tis fun to explore though.
PBR thanks for the proof read, checked notes and had it correct there must have been thinking about something else. To answer your question the initial chassis caster is set a dead load or ride height, upon acceleration or deceleration (braking) the chassis will rise or fall. This will cause the axle to gain or loose caster as its arc passes thru center (ride height). The clamped spring does not pivot at the same point as the sway bar.
yeah, now that I think about it more I can agree with that. A quarter elip spring is not going to act the same way a link would, it would get effectively shorter (from mounting point to axle) as it deflects more one way or the other.
Basically your center single spring is in the wrong plain to do anything except handle a bump that is even on both wheels and that would be rare in real life situations. You need a spring for each wheel location and geometry to allow the wheels to move with bumps without bind or changing angle etc if not it will make it hard to control and steer. Add the other half of the spring and turn it 90 degrees and there you have a system that has survived right until 2008. Not perfect but it does work well.
Very interesting suspension idea there wsdad. I really like the idea of having the spring rate and front roll stiffness independently variable. But I believe that it will lack sufficient lateral stiffness, which will probably detract greatly from having a sharp precise steering feel. A panhard bar would be difficult to fit. but I think it would be well worth the effort to fit some kind of very positive lateral location linkage. The caster change with suspension movement that others have mentioned I do not feel to be a serious issue. Some form of shock damping will definitely be required, otherwise the tires will be bouncing up and down off the road, and if you can see daylight under the front tires on bumps, that is not going to do anything good for either road holding or handling on uneven surfaces. Shocks are especially important where the unsprung weight is fairly high, such as with a beam axle. I believe the idea is basically sound, provided it is made stiff enough laterally, and some form of damping is included. Perhaps some lever type shocks would look less out of place than tubular hydraulic dampers ?
correct in the fact that the center spring will be doing very little aside from supporting the weight of the vehicle, but two spring are definitely not necessary for this to work properly. The important part to controling the roll stiffness of the vehicle, which means the working rate of the sway bar needs to be correct. The Leaf it's self is doing very little to control roll, (as much force as it takes to twist it with 24" of axle on each side as the lever it shouldn't be much) but as soon as the axle becomes un-parrallel with the chassis plane the sway bar will come into play adding roll rate to the vehicle, this would be the car leaning in a corner, or the wheel compressing over a bump, or dropping into a pothole.
He listed that has friction damping built into his sway bar design. Which, although I don't like friction dampers it should work okay, and looks like it could be pretty clean.
Thanks for the replies. I can't seem to get the crude drawing to load onto this forum clearly enough for everyone to see the details. I'll try breaking the picture into 3 pieces and see if that improves things. Striper wrote, "It will allow the axle to rock very freely because the spring won't offer much resistance in torsion i.e. when one side hits a bump, or in cornering there's not much resistance to body roll." You are correct. The spring (in red) will offer no resistance to body roll. That's not its job. It only does two things: 1. It applies downward force on the axle. 2. It keeps the axle from moving left and right. In fact, it will act as a fulcrum. This is overcome by using a stiff sway bar (in purple). "Will the arms have the ability to twist? Obviously you can't bush them at the chassis because that is where your friction material is and so those friction faces will need to stay in contact (parallel) while the axle rocks." Good point. I hadn't thought about that. What if the arms were made out of straight leaf springs or were attached to the axles with ball joints? Unkl Ian wrote, "You probably still need shocks." The picture didn't load onto the forum as clear as it is on my computer so you probably didn't see the friction material between the arms (in blue) and the frame (in black). They would work on the same principal as the ones you get from speedway and other places. Gotgas wrote, judging by the drawing, I think it's too flimsy and unstable for something you want to put a lot of power to and drive fast." The drawing is definitely crude and not to scale. All I have is Windows Paint and I'm not that good at drawing in the first place. One thing that may make it look flimsy is that there are no triangles but there are no triangles on a leaf sprung rear axle either. If it's too flimsy, I'll use heavier parts. If it's too heavy, I'll use lighter parts. Somewhere there's a middle ground where it's not too heavy and not to flimsy. "What about a torsion bar?" That's a tried and true alternative. However, it doesn't look like it has anything to keep the axle from moving from side to side except the stiffness of the flat arms coming off the torsion bar and the stiffness of the flat tabs welded to the axle that the upper rods attach to. I dont know, maybe that's enough? lloning wrote, "Wouldn't you get some twist in the spring??? Maybe not much, but enough to fracture the spring eventually?" If one wheel went down into a ditch at the same time the other wheel went up over a curb, I still don't think it would twist the spring any more than it would on a conventional leaf-sprung rear axle. The wheels are way out on the ends of the axle. They would have a lot of travel before they did any significant twisting to the spring. Also, the eye of the leaf would run through a rubber grommet. The rubber would take up some of the twist, just like on a conventional rear end. PBR Allstar wrote, able to adjust roll stiffness independently of ride stiffness I'm not sure what you mean?" For instance, if I need to change the spring rate by replacing it with a softer leaf spring (the red one), it would have little or no effect on the body roll. If I changed out the sway bar (the purple one) with a stiffer bar, it would have little or no effect on the spring rate (the red one). "A suspension damper... is usually more of a high frequency control, whereas roll and pitch are very low frequency damper controls. Any sort of friction damper is extremely digressive in its ability to handle any high frequency inputs" This is an interesting observation but I'm not sure I understand what you're trying to say. Are you saying that friction shocks don't dampen high frequency movement as well as conventional tube shocks? Or are you saying they wear out quickly when subjected to high frequency movement (such as vibration from road irregularities)? Please elaborate - I can't quite wrap my brain around what you are trying to tell me. "A friction damper is going to offer the same resistance in both compression and rebound, which is way less than ideal and why they went away for the most part on road going vehicles so long ago." Thank you! This is just the kind of criticism I was looking for! I may have to start another question thread asking people how they like their friction shocks. No, on second thought, I'll do a search first. Thank you for making such a good point. To Dolmetsch, Thanks for posting those pictures. I wish there were more pictures. I wish I could see it in person! Thanks for letting me know it can be done. Fifty V8 wrote, "I dont believe 1/4 elliptic springs ever worked all that well as suspension members." Can you elaborate? What is it about them that didn't work well?
wsdad, here's a quick little damper description with some dyno plots, if I was at work I could use some better graphs off our dyno computer but I googled these. The graphs are called force vs. velocity graphs, basically they show the characteristics of of the dampers and how much force they put out (in pounds) in compared to how fast you compress or extend they which is expressed in velocity (inches per second) Typically like I said before, the low frequency movements which for general purposes are ususally 3" per second and below is what is attributed to your chassis dynamics (roll and pitch) whereas your high frequecy movements are going to give your vehicle it's ride quality characteristics (how it takes potholes, expansion joints, etc.) Compression damping is the area above the "0" and rebound damping is the area below the "0" on the force part of the graphs. The compression will often be similar to adding spring rate to the car when it going into compression, basically if you have a shock that is very stiff in compression the car will act oversprung in many ways. Rebound on the other hand will control how quickly the spring unloads after it has absorbed any motion so again, too little rebound control and the car will kind of bounce or float after a "bump" kinda like when you're behind a guy on the freeway and you know his shocks are bad. And, if you have too much rebound control in a damper it will keep the suspension from following the road and say, let the whole weight of the vehicle follow the wheel down into a pothole or something like that. The first graph show characteristics that are common on a modern high performance gas damper, lots of rebound control, little compression control. some people call this a "split valve" damper since it has different characteristics in compression and rebound. The second graph shows a damper that is both similar in compression and rebound, not something that is well suited for a street car, but is very common on a stock car or race car Often times you'll hear drag racers use the term "90/10" shocks for the front, this is just saying the dampers have a lot of compression and very little rebound, so off the line it will transfer the weight to the rear quickly as they extend, yet will not compress easily in order to keep the weight motioned to the rear of the car which is very important, especially if there is a gear change shortly after take off. Now, the problem with a friction damper is that they are very digressive in nature (the dampers in the graphs are both digressive, meaning that they are very firm in the low frequency portion of their movement, but change the characteristic as they increase velocity). A friction shock will have it's highest resistance at "0" velocity, and as soon as it starts to move will drop back down and then be mildly progressive thereafter. I wish I had a graph to show you as I've acctually run them on a dyno before at a shop I used to work at. Now, whether all of this is going to change a hot rod at the end of the day? most likely not, but hey, that's what boards like this are all about, getting some knowledge and some inspiration. I like friction shocks, I like your idea of incorporating them into the sway bar arms. Okay, for my last pic I want to share a hair brain idea that I've had stored away for a long time and just for a flame warning, it uses VW parts!! haha! Not sure if you've ever looked at the front beam on a VW bug ghia or whatever, but they use two sets of torsion leafs (flat spring plates stacked together making a square bar essentially) running through an upper and lower tube. although the leafs are the full width of the axle they are captured in the center, on this one the beam has adjusters in the center allowing you to rotate the pack of leafs to raise or lower the vehicle and keeps the spring action separate left to right. Now what if you took an adjuster, welded that into the center of your tube where you have your sway bar, replaced your sway bar with torsion leafs, and built your arms off the leafs still incorporating your friction shocks? I'm not sure that the spring rate would be right, so that would take some calclulation as far as the width of the the springs, arm length, and axle, but it might offer the right combination of roll resistance and spring rate? Couple that with some nice upper links FED style and it could look pretty trick for readily available parts. I'm still not sure how to get around the side loading problem though, with an FED setup it didn't see sideload or braking load so that could get tricky. I think, as couple people mentioned, you might be able to make your spring arms out of spring steel which would allow them to be able to deflect enough under that rotational load (looking at the way the rear spring arms attach to the axle on my sprint car there isn't a ton of deflection accounted for as rolls) Anyway, hope this all helps, I like it when people go outside the box with ideas!
Something funny happens when springs are used as 1/4's. I am no mechanical engineer, but I always refer back to a hot rodder that tried using them as rear suspension and they were taken off in a short time and of course Jaguar used them on a 60's model sedan, they realized that 1/4's dont work to well so they slid a full length spring in with the other end pushed up into the subframe and a bolt put thru the eye to locate it. Still did not really work, but much better I am told than just the 1/4.
Allstar, Ed Roth built several cars using VW torsion bars to spring a drop tube, I would have to re-read his book, but I have this feeling that he got the ideal from someone at the local drag strip. The 1/4 centre mounted spring, I like, I have seen all the arguements against it, and some of the points are valid, but I actually like the thinking, it's a very simple design, it constrains the axle in all the right directions, I am not that keen on 1/4 springs, but using the spring as an axle location is quite a neat way of making use of it's properties, I don't think I would want to try this set up on the street with brakes on the front axle, but for some thing fairly light on the front with little or no front brakes I could see this working.
I must confess it is a bit funny reading how something you have already built and used succesfully wont work. Always makes me smile. I agree though it is not a street set up , just an intersting experiment. Of course lots of dragster front suspensions would not be practical in daily street use. That should not be a shock to anyone. I am anxious to see how the double 1/4 eliptic works in the new car. As far as turning the spring sideways and adding the rest. It would make little difference in this car since the load point is still in the centre . It would however add about 20 to 30 pounds to the car. And yes I understand that weight will be there with the double 1/4 eliptics so it may be a moot point. Don
PBR Allstar wrote, "Often times you'll hear drag racers use the term "90/10" shocks for the front, this is just saying the dampers have a lot of compression and very little rebound, so off the line it will transfer the weight to the rear quickly as they extend, yet will not compress easily in order to keep the weight motioned to the rear of the car which is very important, especially if there is a gear change shortly after take off. Now, the problem with a friction damper is that they are very digressive in nature (the dampers in the graphs are both digressive, meaning that they are very firm in the low frequency portion of their movement, but change the characteristic as they increase velocity). A friction shock will have its highest resistance at "0" velocity, and as soon as it starts to move will drop back down and then be mildly progressive thereafter." I see the point you're making and it's a good one. I haven't thought of a good way to get around this yet, other than to use tube shocks somehow like Dolmesch did. I need to search the HAMB and other forums to read the debates on friction shocks vs. tube shocks to see how they are "in real life" vs. theory. There's some local car shows here in the DFW area that has some T-buckets running friction shocks. I'll see if I can convince one of them to give me a ride. Maybe I could use some sort of ratcheting device to give me 100/0 shocks, similar to the 90/10's? That still wouldn't solve the high/low frequency problem though. Maybe if we used a wedge to increase the friction as the arc of the arm increased. "if you took an adjuster, welded that into the center of your tube where you have your sway bar, replaced your sway bar with torsion leafs, and built your arms off the leafs" I liked your ideas about using the VW parts. However, if I pictured it correctly in my mind, there would be no sway-bar effect if the adjuster were mounted in the middle of the torsion leafs. Dolmetsch wrote, "I agree though it is not a street set up, just an interesting experiment." Now that you've had some seat-of-pants-feel experience, what specifically is it about this set up that makes you leery of using it on the street? I loved the videos, by the way.
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