Thread: Rearend links- 4 link, 3 link, parellel, angled???

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[QUOTE=mooneye777]

Originally Posted by maddddog

I am building the frame for my 38 Fiat Topolino.
I have looked at pictures, read tech stuff, looked for pictures I saw once but cant find now etc, etc.

What kind of power are you going to be throwing at this Topolino? And what is the endgoal as to where you want it to work best, like street, strip, or both?

Slightly built 454. Maybe it will make a pass down a drag strip but I doubt it. Its for friday nights and full moons only.

It will be just a cruiser with a ridiculous engine and looks. Just for fun.

As I slowly move forward I am getting pretty comfortable with a triangulated 4 bar. I have been messing around with the mock-up and I think I can make that work the best. Not exactly sure how to establish the 8 points of contact on the 4 bars, but I am getting closer with my understanding of what does what. At this point the lower bars are 18" center of pivot to center of pivot. The upper triangulated bars will be maybe a little shorter 16 or 17". That seems to fit in the room I have but final attachment points have not been established in my mind. So, in the absense of knowing exactly what to do, I am just making all the bar components with the bars a little long, hoping I close in on the answer by the time they are ready to finish. That should be sometime tomorrow.
Do you have some suggestions? Love to hear anything you have to say.

Johny joints are cool. Thanks for that 383.

Billy Shope was one of the original Ramchargers, a group of engineers at Chrysler Corporation. I have learned much from reading his writings. Here is some of it.....

"I would also add that, when it comes to the angles (as viewed from the side), pay attention to the OEM setups and NOT to the aftermarket pieces. I saw pictures of one aftermarket arrangement which appeared to have the IC behind the axle, which would mean SEVERE squat on launch. You don't want that. If you want to eliminate squat or rise entirely, arrange the links so that lines through them, as viewed from the side, intersect on a line which passes through the rear tire patch and has a slope equal to the CG height divided by the wheelbase. If the intersection is above this line, the car will rise on launch; if below, squat. It's not necessary for either pair (top or bottom) to be level."

he explains further......

"In the side view, visualize a horizontal line through the center of gravity and a vertical line through the front tire patch. Then, a line...called the "no squat/no rise line"...passing through the intersection of these two lines and the rear tire patch.

Finally, visualize lines passing through the centerlines of your links. There will be an upper line (through the upper two links) and a lower line (through the lower two links). If you don't want the car to squat or rise, arrange the links so that the intersection of the upper line and the lower line falls on the no squat/no rise line. If you want it to rise, put the intersection above the line; squat, below the line."

Editors note: Without knowing exactly where the center of gravity is, a fairly close approximation can be made by using the camshaft height as viewed from the side of the car. Sitting down with pencil and paper and drawing the arrangement out to scale will get you in the ballpark.

Thanks Techinspector.

I wish I knew how to find some of those lines he talks about. I read that exact piece yesterday.

A picture is worth 10,000 words. Any idea where to find that kind of stuff sketched up?

What techinspecter has said is very very true, But on an equal note you are looking for a cruiser. Even though what he has said is crucial you are not starting with a race car or even a daily driver car in the end. I know you will have to work with what room has been given to you. What he said would be great to start with if you didnt have anything started and wanted to design a great handeling car from the start. Take your bar lengths you have start with some mounting (where you think they can go) and move the rearend assy to see what happens, with your pinion angle, and shock movments. After all said and you think is done. I dont know what fabrication or design skills you might have but I think you might have a rough time with what He has given you to do. Now I hope you best of luck. There is alot of great information here. You will be the guy that will have to decifer all the info. Oh and a triangulated 4 link isnt a bad setup. Just watch your upper bar angles not enough and there rear will move side to side.

best of luck.

Thanks Stormstyle.
I have good fabrication skills and equip. The angles on the upper bars will be substantial otherwise the forward mounting bracket will be into the back of the seat.

Well you will just have to remember that you upper bar angles and lower bar angles are all in relation to each other. or your pinion will rise/ dive quickly. That will be a situation to pay alot of attention too. Will this car have air ride or adjustable suspension? Whats the total wheelbase on this project too?

Wheel base is short, something like 93".
No air ride. Coilovers and I dont expect to have much travel. I am leaving 4 inches of travel from ride height before the bump stop.

Too much? Not enough? Please feel free to offer any and all opinions.

Yesterday I made these parts while I try to figure out exactly what to do.

OK, let's say that the wheelbase is 110" and the cam is at 20" above the ground. Let's also say that the center of gravity is halfway back on the car at 55". To nail this down, you'd have to weigh the car and figure front weight compared to rear weight, but we'll use 50%.

Starting with a piece of paper that is 14" long will get this done. We'll use 1/8 scale. Dividing 110 by 8 will give you a wheelbase on the paper of 13 3/4".

Draw a horizontal line on the paper about an inch from the bottom of the paper. This will represent ground.

Line A will be the cam height and will be represented by a horizontal line drawn on the paper 2 1/2" above the ground line. (20 divided by 8).

Line B will be a vertical line to represent the centerline of the front wheel. Draw this line 1/8" from the left side of the paper.

Line C will be a vertical line drawn at the other end of the paper, 1/8" from the right end of the paper. This will represent the centerline of the rear wheel. Now, your two vertical lines should be 13 3/4" apart to represent the wheelbase.

Place a dot on the cam line halfway in the middle of the paper (6 7/8" from Line B and 6 7/8" from Line C). This will represent the center of gravity.

Place a dot at the intersection of Lines A and B. Place a dot at the intersection of the ground line and Line C. Ground/C dot will represent the contact patch at the rear tire on the ground.

Draw a line from the dot at the intersection of lines A-B to the dot at intersection of Ground/C. This will be the squat/no-squat line.

Measure the rear connection points of the top and bottom connections of the links and make dots representing these points on line C (or just forward of line C or just behind Line C, depending on exactly where they are in relation to the rear axle).

Draw a line from the dot representing the top link rear attachment point to the squat line directly below the CG. This will represent the angle of the top link.

Draw a line from the dot representing the bottom link rear attachment point to the squat line at the intersection where the top link line was drawn and intersected the squat line. This will represent the angle of the bottom link.

Measure the length of the actual top link and transfer the measurement to the drawing (link actual measurement divided by 8). Make a dot at that point on the top link line.

Measure the length of the actual bottom link and transfer the measurement to the drawing (link actual measurement divided by 8). Make a dot at that point on the bottom link line.

There, done. Measure the distance from the ground line to the bottom link front attachment point on the paper. Multiply by 8. Now you have the actual measurement from the ground for the front attachment point of the bottom link.

Repeat for the top link.

Thanks Techinspector!!
I think I actually understood that.
I am headed out the door for an all day road trip to pick up my bucket seats otherwise I would draw this out and ask more questions right now.

Thank you so much for taking the time to do this. I knew there was a science to it but with all my searching on the web, I didnt find it.
I did find a spread sheet that you could enter your numbers in and it had a diagram, but I cant find that now either. Sometimes too much information is not a help.

I will surely have more question when I get back and get into it.

Originally Posted by DennyW

Here's Billy Shope's web page. Lots of info, and calculators.

http://home.earthlink.net/~whshope/

DennyW, thats what I'm talking about . Ready made pictures and lots of words in big type. I just took a quick look and was very impressed. I got some reading to do.

I spent a couple hours reading on Billy Shop's page last night.

It almost makes sense too.
Whats your vector, Victor?
It is mostly about racing.
I keep reading that for street use, the setups are slightly different.
I guess I will just have to keep on reading.

See this is why I like this site. I can even learn quit a bit more. This is a great site. Thanks

Originally Posted by Itoldyouso

Yep, it has more travel than one would think. I have jacked up one side of the axle when working on it, and it goes up quite a bit with no binding. They use these on lowriders and those guys put them through some crazy angles, leaning to one side, etc. On the typical hot rod, the wheels really don't move up and down all that far anyways. Maybe a couple inches at the most.

It really is a pretty simple solution to the length problem.

Don

I got the bushings for the 4 link today from speedway.
They are very hard, like delrin or something.
How are hey suppose to squish when rhe rearend twists?

Ummmm, I don't think they will dog. Maybe a little better than steel-to-steel, but not compliant enough for me on the street. Gimme rubber.

Originally Posted by techinspector1

Ummmm, I don't think they will dog. Maybe a little better than steel-to-steel, but not compliant enough for me on the street. Gimme rubber.

Where would I get rubber?
I havnt seen it.