4 bars should be parallel and even in length. This I know. I'm trying to find some compromise to run a tube axle but I absolutely hate the look of a 4-bar. This would be far less offensive to my eye. With this setup, the upper links (quarter elliptical springs) would be about half the length of the lower links. I know this means that as the axle travels up, it will lean back more. While it's not really something you want to happen, seems like that would actually assist in keeping the car going straight. Not such a good thing while turning though. On paper, and from an engineering standpoint I know it's not right. But.....with as little suspension travel as there is on these things, is it really that impractical? Would the couple degrees of change really be that horrible? Or does the uneven length completely negate the point of using a 4-bar to allow the tube axle to work without twisting? Need some input....thanks!
We have a all out 80's street rod in the Shop now. 1932 4 dr sedan, Had a tube axle, split 32 wishbones, and over 100,00o miles. I know you aiont supposed to do it but it sure held up on this one. Of coarse we are putting it back like it needs to be but it aint broke. Rusty
I have a buddys T modified at my shop right now that has quarter elliptic front suspension on it. Seems to work well, as I have driven it. Drives like any other hot rod, I've driven. Maybe a little better due to radials on the front. PM me your email address and I will send you all the pictures you want, if that will help.
So what do you think is wrong with your idea?, Since you have a drawing program just plot this out in three views. Use 4" of travel as your base line for the range of movement for the suspension. This will show any potential trouble spots. The longer you make the lower radius rod the shallower the arc created and the less caster gain so that should not be a problem. You should chose a spring with a thinner leaf to allow some degree of twist to compensate for the rotary motion as the axle goes over uneven surfaces. One issue is to determine the relationship of the spring eye mount to the radius rod axle mount so they operates within parallel arcs.
I'm not sure what the problem is I can't figure out the drawing very well,This is how I did mine and it drives great. Used 57 chevy springs,stiffer shorter half in front and the longer half in the rear. The spring holds the bottom of the axle just the same as a bottom bar on a four link,and still provides spring action. On the rear I angled the top bars to eliminate the need for a panard bar or track link. If you have any questions i'll try to help
Thanks for the input Dick. The issue I was foreseeing is that the upper link (the spring) is shorter, making it's arc radius smaller. The longer lower link would have a broader arc. So when the two travel together, the upper link will move more than the lower, causing the axle to roll back and forth instead of staying straight up and down through it's range of travel. The difference between the movement in this and an equal length setup may be very minor and I might be creating a lot more concern than is needed. I doubt there would be more than 4" total up and down movement. But I thought I'd check anyway! Joecool - yours is one of the setups I'd looked at when I started thinking about quarter elliptics. Two things I want to do different....mine would be reversed with the spring on top. I want to hide as much of the spring inside the frame rail as I can. Almost every quarter elliptic setup I see uses secondary links that are the same length as the spring, which means they are usually very short, which I don't really like the looks of. I want the lower link to look like a wishbone, which means long.
I used split wishbones on mine...with quarter eliptic springs and shackles mounted to the axle....drove nice!
The whole idea behind all this compromise is I want to use a tube axle, so I've ruled out using split bones if I go that route.
Depending on the amount of arch in the spring you will push the top of the axle forward when the wheel moves up and reward when the wheel moves down. The distance from the spring mount to the eyelet will increase when you hit a bump. That will cause a slight decrease in king pin inclination. The opposite will happen when the spring rebounds. Leaf springs act kinda weird when compressed too. So.... What about two leafs on each side?? Harry Miller's front wheel drive Indy cars used upper and lower 1/4 elliptical springs to eliminate conflicting axle travel. Check out Miller-Offy historical web site for photos.
I couldn't view your drawing full size (just that crappy 'loading' window going round in circles), but my question would be, "how is the spring fixed to the axle?" As the bottom link will have a pivot at both ends, the spring will have to be fixed, without shackles, so I guess you will have a bush in each spring eye, and two pairs of brackets on the axle with a bolt for each spring? As D.S. said, the springs will need to twist, and the way I picture it you will still also get some of the 'wishbone' type twisting moment on the axle (I could be wrong on this)? Rubber bushes in the spring eyes would help reduce amount of twist on the springs.
Been looking at this kit from Posies. Will take some modifications to the mounting bracket to work inside the frame rails, but I do like the built in ride height adjusters. I would not be using the shackles with it. I'd have a bracket welded to the axle that would sandwich the spring eye. Would use standard shackle bushings. I would think there has got to be enough flex in all this to work well here.
I agree with the double quarter elliptical setup. It seems to solve all you problems. Unless of course you want the wishbone look. Just in case you haven't seen it here's the miller site. I set my rear up like this. I haven't driven it yet but it sure seems like it's going to work great. http://www.milleroffy.com/Photo & Sound Gallery.htm
By the way I used the posies kit on the bottom and cut in half and drilled posies spring on the top. I think the posies kit is only worth the money if you are going to adjust height a lot.
No the shorter radius is off set by the longer radius rod and the minor arch of the spring main leaf. By using longer radius rod that sweeps an arch of say 6* in a 4" travel, even thought the spring has a shorter center the location of the spring arc in relation to the rod, the arcs can be compared and you will see that actual induced caster gain during compression is minimal. Where you see much more caster gain is during drop when you would be hitting a pot hole and this may be beneficial in helping maintain straight line steering. If you refer to Joecools pictures his is exact opposite of your idea and it it may initiate a slight caster loss during bump and a caster loss during drop. What you can do, to balance this, is offset the vertical mounting position at the axle and bring the operating arcs more concentric with each other. You can easily plot this out on the kitchen table with a string a pencil and a tape measure and just run the arcs.
Makes sense Dick. Thanks again. Looks like I'll be going this route when I get around to building my chassis.
When I built the front end on my lakes mod. ,I didn't worry about castor change,it's controled by the length of your wishbones or hairpins. That said ,you need to have shackels between the spring and the axle. My 52" front bones don't give much arc with 4 to5'' travel. ...........Jack
I am using a 4" drop tube axle, quarter elliptics and hairpins on the car seen as my Avatar. It is one of the "Real Hot Rods" car produced by Real Hot Rods of Michigan, modified with a Whippet grill shell and Pontiac headlights. The suspension works fine, the travel is so small that any strain is spread over the entire suspension negating any problem. Another of these cars that I know of is in Tennessee, originally from Calif. Seen in numerous event stories, it has a no. 36 on the doors, and has lots of miles without incident. Go for it with hairpins and enjoy the look and none of the design hassles your having now.
My sr dragster has a 3 link but that is not relevant because it could have 4 just as easy. In fact i am making a four ink with 1/4 elip on the hemi jeep deal. Put the spring on the bottom and a couple of short (same length) radius rods on the top. That will eliminate a caster change on bumps. With the dragster I did it a bit different but it works perfect . The radius rods are a bit longer but only 6 inches and is seems to help the car instead of hurt it. The car goes incredably stright. In fact drive it with one hand and never need to correct it at all . I was pleasantly surpised how well it worked. You may be able to see enough on my website (below) I am hoping to have the other front end done by Christmas so if you wish you can watch that as it progresses. I like 1/4 elips a lot.
Spooler - this setup wont need shackles. With hairpins or a wishbone, they are what holds the axle in place. The springs need the shackles so the axle can move with it's control arms and the springs wont bind. When using the spring as one of the control arms, a shackle would just let the axle flop around....hit the brakes and it would fold under. Dolm - The spring on the bottom might be a better idea so I don't have to raise the frame up so much. But in wanting to keep the springs and radius rods parallel, I'm worried about how high I will need to mount the rear end of the rod on the frame. I'd like to keep it below the top edge of the frame rail, instead of having to build a bracket to mount it on top. That is all something I'll have to figure out when I actually start building it. The short, same-length radius rods are exactly what I'm trying to avoid, and why I raised the question in the first place. I really don't like the look of those at all. I want the longer rod so it has look of bones. In fact, I'm really considering making the radius rods out of a wishbone with an adjustable end at the rear, and a solid 4-bar style mount up front.
The radius of the arc will be longer since...as the spring straightens it gets longer. When you do your drawrings As Dick suggested....Use the length of the arc of the spring for your dimension at 2" up. ( Not the length from mounting point to eye center. At this point the spring should be almost all the way flat. I have mixed opinions of what it will look like at 2" down. IMO Dan Webb did the best version of this set up on Ashleys Black 32.
if im not wrong , early sprint cars (modifieds then) used Quarter Elliptic front end .......... steve
I'm wondering about the effect of pushing the spring from the front. Also, I'm thinkin' springs aren't great way to locate the position of the steering axle. The leaves do some squirmin' don't they?
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