Track Width and 4-link

[BBPanel]

Have a 55 Chevy setup many years ago w/Alston ladder bars and it is back-halved. Distance between rails is 26". Its Pro-Street all the way. It looks like I could probably convert it to a 4-link w/o too much effort but is it worth the trouble? Car will be a cruiser primarily and fair weather only.
I guess my first concern is the track width - any rule of thumb that need be adhered to with a 4-link?
A TQ Arm isn't out of the question either but would like to address the 4-link specifically. -Bob

[Ron Sutton]

I'm a little unclear on the question about track width. Are you asking if the 4-link influences the proper track width of the tires? Or are you using the term track width in asking how wide to place the 4-link?

[Ron in SoCal]

Welcome Ron! About time... :D :cheers:

[Ron Sutton]

Thanks SoCal Ron. Should I be NorCal Ron? LOL

[BBPanel]

.... Are you asking if the 4-link influences the proper track width of the tires? Or are you using the term track width in asking how wide to place the 4-link?
I guess I used the term track width to define the distance between the ladder/4-link bars. I assume the distance for ladder bars is not particularly important because its primarily a straight line suspension. But people run the 4-link because it articulates better when doing things other than going in a straight line. The stock frame rails are ~40" apart and many people run 4-links with the stock frame. If I convert to a 4-link the distance between them will be >14" narrower. Will this impact the effectiveness of the 4-link? There has to be some distance where its impractical and I'm trying to determine what that might be.

[Ron in SoCal]

Thanks SoCal Ron. Should I be NorCal Ron? LOL

Just be yourself and we'll all benefit. :thumbsup:

[Ron Sutton]

Now I understand. Thanks for clarifying.

The further outward you place the suspension pieces, the more control they have. This is most critical with shocks, and to less degree with springs ... but also applies, to a lesser degree, to suspension arms that act as "levers".

You stated earlier that the frame width is 26" between the rails. Assuming your frame width is 2" (correct me if I'm wrong) ... that makes the frame rails 28" center to center.

If you're able to place your 4-link under the frame rails, 28" center to center will be very good. Something to ease your worries a little bit ... the narrower the 4-link is ... the better it articulates (rotates within the chassis).

In fact, in monster tire Pro/Mod drag cars ... where the tires are so mondo wide ... the space for the 4-link ended up pretty narrow. This was such a problem that drag chassis builders had to start adding sway bars ... in drag cars. :-)

-------------------------------------

On another note ... or two ...

1. I suggest you figure out how far outward you can mount the shocks & springs. Get away from how drag race car builders do this (on the back of the 4-link). The wider you can mount the shocks (and springs if coil overs) ... the better the motion ratio ... and the better control the shocks will have on the rear suspension. If the springs & shocks are separate & you have to choose ... shocks further outboard trumps springs. Really push the packaging of this to get the max.

2. If you really want your rear suspension to articulate ... even better than the 4-link ... and if you're NOT going to drag race it HARD (High hp, slicks & high rpm launches) I would suggest you consider a 3-link with a panhard bar. Another option, if you're going to drag race it still, would be a triangulated 4-link. It can be as strong as a regular 4-link, but with one set of bars angled together to form a triangle ... allows it to act "similar" to a 3-link in terms of increased articulation ability.

Again, not trying to take you off track. Just want you find what's best for your situation.

Best wishes !

[BBPanel]

......If you're able to place your 4-link under the frame rails, 28" center to center will be very good. Something to ease your worries a little bit ... the narrower the 4-link is ... the better it articulates (rotates within the chassis)....
Hmm, that seems a little contradictory - move them outboard and under the frame rail but narrower is better?

I could probably locate the lower bar under the frame rail but what about the upper - it couldn't be in the same vertical plane - is that a problem?

As for the triangulated 4-link, i thought there were some guidelines on the ratio of the lengths of the upper and lower bars (I don't recall what they are) and very narrow frames don't work out well. Is that true?

All in all it sounds like if I replaced the ladder bars w/4-link in the same location they are now its not a problem. -Bob

[Ron Sutton]

Hmm, that seems a little contradictory - move them outboard and under the frame rail but narrower is better?

I could probably locate the lower bar under the frame rail but what about the upper - it couldn't be in the same vertical plane - is that a problem?

As for the triangulated 4-link, i thought there were some guidelines on the ratio of the lengths of the upper and lower bars (I don't recall what they are) and very narrow frames don't work out well. Is that true?

All in all it sounds like if I replaced the ladder bars w/4-link in the same location they are now its not a problem. -Bob

Sorry if I my post wasn't clear. I didn't say narrower is better. It's not. Narrower simply offers more articulation (roll within the chassis) & wider offers more control. The lower bars affect roll steer the most. The width, angle & length of the lower bars all affect roll steer. 28" wide is fine & will work well, providing all the other suspension components & geometry are correct.

Having not seen your frame layout, I couldn't recommend the best layout. If you post some photos, we may be able to offer ideas.

Having upper bars on different vertical plane is not a problem. Mounting them inside your frame rails (therefore narrower) would allow the rear suspension more articulation (roll within the chassis).

There are guidelines on the ratio of the lengths of the upper and lower bars on triangulated & parallel 4-links. But if you ask 6 different designers/engineers, you'll get 6 different opinions based on their experience, or lack of. There is no absolute ratio.

[BBPanel]

Not the best picture but ....:

http://img.photobucket.com/albums/v203/BBPanel/55%20Belair/IMG_1501_zps5ac7c045.jpg (http://smg.photobucket.com/user/BBPanel/media/55%20Belair/IMG_1501_zps5ac7c045.jpg.html)

[Ron Sutton]

Hmmmm ...

The rear frame was definitely built for ladder bars. There is no room under the frame for the upper bars, and even the lower bars would have to be short. Too short. (Shorter bars make the pinion angle change more drastically. Longer bars = less change).

You can install the 4-link in the same place the ladder bars are now.

This isn't optimum, by any means, but it would be a significant improvement over the ladder bars you currently have, which go into bind almost the instant the car experiences any body roll.

I would package them as close to the frame rail as possible, say 1" space between the front outer 4-link bracket & the inside of the frame. (Just enough for a nut & wrench) That will position the 4-link around 23" center-to-center.

If you were building a car, you wouldn't do it this way. If you ever decide to re-do your rear frame, you would want to design it so the 4-link goes under the frame rails. You can look at Chris Alston's Chassisworks rear subframes to visually see this. Here is a link, in case you haven't already seen them:
http://www.cachassisworks.com/c-491-eliminator-ii-3x2.aspx

(For that matter, if you were to re-do this car as a pro-touring car, you wouldn't do it like this at all.)

To help the rest of your package come together, I have some tips:

1. Use "misalignment spacers" on both sides of all 4 rod ends. This is key to allowing more articulation without bind. The 4-link can still bind. It just has more range before it does.

2. Place the shocks & springs as far outboard as possible. I would push the packaging here. If you use coils overs, mount the top of the shock on the crossmember & the bottom mount on a long, sturdy bracket (with angle brace to housing) on the rear end housing. Angle the top of the shock inward at 10 degrees & push both mounts as far outboard as possible (keeping 1/2" clearance between the spring & frame). This width of shock & spring will add stability & control, as opposed to mounting them narrower.

3. I am a fan of panhard bars only when they can be long & adjustable on both ends. In this application, a panhard bar would be on the short side for my tastes, causing excessive sideways movement during travel. It would work ... just not preferred.

I would lean towards a watts link to keep the rear end centered. I always make mine adjustable (for roll center tuning), and even then, you need to get the roll center "in the ballpark." If you're concerned about body roll, you may want to mount the roll center in the higher range. If you were Autocrossing (doubtful?) you may want it in the lower range.

Best wishes !

[Chassisworks]

Thanks for posting a link to our page, Ron. You're such a good neighbor. :)

BB Panel-
I can see that this car has our Battle Cruiser adjustable ladder bars and the econo coilover kit. (The frame is not ours.) The best thing to do in this situation would be to cut out the rear rails and do an entirely new backhalf. If that is not an options, here's a couple things to consider.

These bars most likely measure 32" from axle centerline to the front rod end bolt. Putting a 4-link in this frame would mean welding in a new crossmember closer to the rear which isn't impossible but I would be concerned about frame rail clearance.

Check out THIS BUILD ARTICLE (http://www.cachassisworks.com/Stories/HowCAC-009_WEB.pdf)for details on how this might be accomplished. I know it shows a pickup but if you're trying to work with what you have, it's essentially the same process and the components are the same.

[BBPanel]

Thank you for the input - looks like some changes are probably in order. -Bob

[wedged]

You might want to take a look at this and a few of the pages after : narrow Triangulated 4 link (http://www.lateral-g.net/forums/showthread.php4?t=21869&page=8)


It was designed with input from members of this site. designing thread (http://www.lateral-g.net/forums/showthread.php4?t=28788)

[BBPanel]

You might want to take a look at this and a few of the pages after : narrow Triangulated 4 link (http://www.lateral-g.net/forums/showthread.php4?t=21869&page=8) It was designed with input from members of this site. designing thread (http://www.lateral-g.net/forums/showthread.php4?t=28788)
Sorry, I've been unable to respond for awhile. And thanks for the link - I remember that thread but was having trouble finding it. -Bob