rear suspension design help needed [Archive]

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wedged

10-03-2010, 12:49 PM

I'd like some opinions on how I should build the rear frame and suspension. I'm not trying to build the ultimate road course truck but I would like good handling. The easy way out is ladder bars and a panhard bar, but the handling is not great. I want to make a triangulated 4 link system and use urethane bushings instead of rod ends. If anyone with a suspension analiyzing program can help, I sure would appreciate it !

Here are the spec's for the space available:

tires bulge to bulge 33"
I have 2"x4" box tube on hand- max width O-O of frame rails 29" ?
wheel base 116"

The rear I will be using is a Dana 60

Mostly what I'm looking for is recommended link bar length and angles of the link bars, vertically and horizontally.

I'm figuring the lower bars should be parallel to the vehicle center line and the uppers angled from outboard on the axle tube to an inboard mounting point.

http://www.bigblockdakota.com/stuffed06.jpg

http://www.bigblockdakota.com/stuffed05.jpg

http://www.bigblockdakota.com/stuffed01.jpg

wedged

10-05-2010, 04:25 PM

wow. over 80 views and no one has any thoughts ? OK, how about if we pretend it's a first gen camaro instead of a Job Rated Dodge truck ? :wow: :rofl:

ROKN69

10-05-2010, 05:34 PM

Nice truck! I wish I could contribute more than this, but fabrication and I are not speaking to each other, as I have little to no skill in that regard.

exwestracer

10-06-2010, 10:30 AM

wow. over 80 views and no one has any thoughts ? OK, how about if we pretend it's a first gen camaro instead of a Job Rated Dodge truck ? :wow: :rofl:

Actually, you've probably got a better starting point for a tri-4 link with your truck...:D

Some general guidelines:

Keep the lower links level with the ground at ride height.
Mount the upper links together on the housing, and apart at the frame (complicated explanation having to do with roll center location deleted)
Minimum of 60deg included angle ("V" angle) between the upper links.
Upper effective link length should be roughly 70% of the lower links (this is in side view, NOT the actual hole to hole measurement of the angle link).
Upper link angle (side view) is impossible to determine without more info, but they should intersect ("IC")with the lower link line no further than the front axle centerline (see drawing)

http://image.chevyhiperformance.com/f/9559246/148_0309_guide_sbr_z.jpg

You will find that your narrow frame width will make it difficult to get both the 60deg included angle and 70% link length ratio for the upper links. Stay with the 60deg minimum for stability. You're not going to be looking at a lot of suspension travel, so the pinion angle change should not be a major issue, especially if you keep the intersection (IC) of the link angles in the front half of the wheelbase.

Hope this all makes sense.

wedged

10-07-2010, 06:44 AM

Hope this all makes sense.

Most of it :thumbsup: Thanks !. Any particular length for the bars, or should I base the length of the lowers on how long I can make the uppers ? I'm not too concearned about retaining bed space, so I can make my frame any way I need to in order to accomodate the suspension.

I'd like to hear more about centering the uppers on the housing as opposed to centering on the frame, which is what I was considering. It's easier to weld to the axle tubes than to the cast center of the Dana. I can always make a bracket for mounting to the center of the diff. If you don't feel like typing and know of a link, that would be great.

The upper and lower link points on the housing will obviouly be seperated vertically. Is there any specific distance I should aim for ? And should that distance be equally divided above and below the axle center line ?

ironworks

10-07-2010, 08:00 AM

For the situation you have a tri 4 link will be tough. I would do a standard 4 link with level lower links at ride height. Make the lower links 30-34 inches long. Make the uppers 70-100% of that length. Set the instant center at about the bell housing of the top hole and just lower the second adjustment hole about .75 of and inch on the front upper mount on the chassis. Then build a pan hard bar that is level at ride height and as long and low as possible. Then mount the shocks as far out on the axle as possible.

This is super basic set up that will get you started, Could you design way more high tech set up sure, But at the end of the day this car will never sit on the Pole at Daytona.

Key points - level lower links and pan hard bar at ride height. The longer the panhard bar. The longer the links the better the ride quality. I have been told that after 34 inches it does not matter. Ideally you want the center of Gravity below the Roll center.

Ready Set Go

Kenny

10-07-2010, 09:18 AM

The advice these guys have given is good stuff. The only thing that I would add is the link length...... The shorter the bottom link, the higher percentage the top length should be. So let's say you end up where you only comfortably fit a 20" bottom link, then you will want closer to 20" on the top. That would reduce some of the bind during roll that would be created with a much shorter link. To give a point of reference on that length, it is 19" (if my memory is correct) on 3rd and 4th gen F-bodies. That length seems to work fine as roll steer goes, but longer would theoretically be better.

When working on "bagged" suspension that has a fair amount of travel and using 22" lower links on a shorter wheelbase than yours, the bind from using shorter 18" angled upper links would split poly bushings and kill u-joints. Replacing the urethane with rod ends made the ride quite harsh. Simply moving the upper mounts and going with 22" uppers brought this back where it should be.

Usually these projects "evolve" quite a bit during construction...... So the choice of these upper link mounting styles you choose, and how much pinion angle change you want, will dictate the length ratio...... Of course that is only one man's opinion.

Beautiful project BTW :thumbsup:

exwestracer

10-07-2010, 10:16 AM

Most of it :thumbsup: Thanks !. Any particular length for the bars, or should I base the length of the lowers on how long I can make the uppers ? I'm not too concearned about retaining bed space, so I can make my frame any way I need to in order to accomodate the suspension.

I'd like to hear more about centering the uppers on the housing as opposed to centering on the frame, which is what I was considering. It's easier to weld to the axle tubes than to the cast center of the Dana. I can always make a bracket for mounting to the center of the diff. If you don't feel like typing and know of a link, that would be great.

The upper and lower link points on the housing will obviouly be seperated vertically. Is there any specific distance I should aim for ? And should that distance be equally divided above and below the axle center line ?

Yes, figure out the maximum effective length you can get for the upper links with 60deg included angle and build the lowers from there.
If it were me, I'd buy one of those heavy duty steel rear covers they make for the off-road guys and weld the upper link mounts to that...
I just typed the explanation for the direction of the links over on pro-touring, so feel free to have a look... http://www.pro-touring.com/forum/showthread.php?t=73355 The main issue I see with your project is fenderwell clearance looks pretty tight. I think I'd want as little axle movement as possible.

As far as the vertical link separation, it all depends on how hard you are realistically going to hammer the thing... Obviously if you mount the uppers at the top of the diff, you've got some separation built in already. I normally try to keep the lowers feeding directly into the main frame rails, as they are taking ALL the drive force from the axle, so your ride height for the frame would come into play with how far your lower housing mounts are off the ground.

If you decide to go with a straight (4 bar) setup as others have suggested, IMO you have way too much tire (not enough room) for a panhard bar locator.

ironworks

10-07-2010, 10:46 AM

Yes, figure out the maximum effective length you can get for the upper links with 60deg included angle and build the lowers from there.
If it were me, I'd buy one of those heavy duty steel rear covers they make for the off-road guys and weld the upper link mounts to that...
I just typed the explanation for the direction of the links over on pro-touring, so feel free to have a look... http://www.pro-touring.com/forum/showthread.php?t=73355 The main issue I see with your project is fenderwell clearance looks pretty tight. I think I'd want as little axle movement as possible.

As far as the vertical link separation, it all depends on how hard you are realistically going to hammer the thing... Obviously if you mount the uppers at the top of the diff, you've got some separation built in already. I normally try to keep the lowers feeding directly into the main frame rails, as they are taking ALL the drive force from the axle, so your ride height for the frame would come into play with how far your lower housing mounts are off the ground.

If you decide to go with a straight (4 bar) setup as others have suggested, IMO you have way too much tire (not enough room) for a panhard bar locator.

Your correct, but since he has the big wheels he can make the panhard bracket go out into the wheel to increase the length. The frame rails will be pretty narrow due to the wide tires so the angled upper links will be pretty short to have any kind of angle especially if the he does not want to build off the housing.

But either way, both methods will require creative packaging for either the upper links or panhard bar

Chassisworks makes a rear clip that is a nice tri-4, You can buy the links and the axle housing and save your self a bunch of time. They might make a jig to install these parts on a dana 60 housing. We have used this product on quite a few different cars with good results.

http://www.cachassisworks.com/Attachments/Instructions/916241.pdf

exwestracer

10-07-2010, 11:45 AM

This is true, but the frame end of the panhard would still be close to chassis centerline. I always try to keep the panhard centered on the chassis, so the roll characteristics are the pretty much the same in left and right turns. Probably doesn't matter, but I figure you can't go wrong doing it that way...just my $.02...

wedged

10-07-2010, 11:48 AM

Now we are getting somewhere ! Thanks everyone.

just to clarify a few things:

I will end up with at least 1" clearance from the tire to any body sheet metal, probably closer to 1.5". In the pictures it's at about 1". I'll build the rear axle to be about 1" total narrower than I want and then I can use thin spacers to dial in the final width.

For the mounting the upper links, I had already thought of the off road diff or making a tube bridge over the diff to weld mounts to. There may even be diff covers with mounts already on them, but I have not searched enough yet.

I will probably start with coil overs, but may eventually end up with bags all around. I'm just not sure if I want to add the tank, compressor, etc.

Am I correct thinking the uppers are 60 degrees compared to each other and not an upper compared to a lower ?

I just test drove a pro street '68 barracuda that I put a new set of gears and one new axle into. It's a ladder bar car with heim ends. I'm not putting up with the constant clunking and clanking and that's why I want to use urethane in the truck.

I also have a '68 satellite in the shop that has an Air Ride 4 bar in the rear. I had thought of taking measurements off of it, but I feel that set up is compromised from being ideal in order to be a bolt on kit. So why bother copying it ?

exwestracer

10-07-2010, 01:20 PM

You probably won't find a diff cover with exactly the mounts you are looking for, but there are some out there that would be a good start. I wouldn't bother with the bridge on that Dana 60...a 10 bolt is a different story.

You are correct about the 60deg referring to the angle between the 2 upper links.

wedged

10-09-2010, 02:48 PM

exwestracer

10-10-2010, 01:20 AM

I made a quick 2d overhead view cad drawing. O-O of the rails at 30.0", upper links mounted 6" apart on rear. I came up with 58 degrees included angle with an effective length of 18" for the uppers. Using the 70%-100% idea, the lower links would be 26" or less. I forgot to dimension the actual length of the uppers.

If i kept the frame rails wider in front of the tires, or had a crossmember in directly in front of the tires, I could make the upper links longer.

I'm going to fiddle around with the drawing and see what i can come up with.

I usually try to get the uppers really close together on the axle, to help with angle/bar length and keep the roll center close the axle centerline. I've found we can get johnny joints down to 4" apart on center, and 3/4" heims down to 2" on center. If clearance above the housing is an issue, you'll obviously have to move them further apart to get them lower.

wedged

10-10-2010, 08:34 AM

I think I can probably get the mounts closer together on the housing, but i figured 6" was a decent starting point. I don't have any clearance issues above the housing as I'm not too concearned about bed space.

Does it matter where the forward mount points of the upper links land in relation to the lowers in an overhead view ? I know they are typically inboard of the lowers, but could they be outboard ? The front frame from the dakota donor is about 38" to the outside. I could extend those rails back as far as I can in front of the rear tires, before squeezing it down to fit between them.

wedged

10-10-2010, 04:09 PM

I found some joints and brackets and bushings that will probably work well to build the links. They also have very heavy duty Dana 60 covers.

http://www.ballisticfabrication.com/thumbnail.asp?file=assets/images/bushing/263weldonbushing_thumbnail.jpg&maxx=0&maxy=150

http://www.ballisticfabrication.com/thumbnail.asp?file=assets/images/ballisticjoint/3inchbj_thumbnail.jpg&maxx=0&maxy=150

http://www.ballisticfabrication.com/thumbnail.asp?file=assets/images/newbrackets/bj4linkmount_thumbnail.jpg&maxx=0&maxy=150

http://www.ballisticfabrication.com/thumbnail.asp?file=assets/images/newbrackets/4linkadj_thumbnail.jpg&maxx=0&maxy=150

http://www.ballisticfabrication.com/thumbnail.asp?file=assets/images/diffcover/dana60diffcover_thumbnail.jpg&maxx=0&maxy=150

exwestracer

10-11-2010, 03:37 PM

wedged

11-06-2010, 11:45 AM

I played around with the crude CAD drawing, keeping the rails between the tires at 30" O-O and the rails in front of the tires at 38" O-O. I was able to make the upper bars have a 23" effective length with a 70 degree included angle. The actual length was 28". Would 28.75" be a good length for the lowers- that makes the upper effective length 80% of lowers ?

In the drawing, the frame starts to widen from 30" to 38" at a point 18" in front of the axle centerline for clearing the 29" diameter tires.

This may sound weird, but I'm getting excited about the possibility that this is going to work out well. :willy: :dance:

exwestracer

11-06-2010, 12:20 PM

wedged

11-06-2010, 03:12 PM

I'm planning on making a crossmember that will be a driveshaft loop and front lower bar mount. I stilll need to make a front loop and trans crossmember but I'm going to build the rear suspension first.

wedged

12-21-2010, 08:03 AM

I found some more info right here on this site. I don't know why it didn't show up when I searched the first time :

Here are a few basics to keep in mind as you do your reading :)

Roll Center Height: If you have one pair of angled links, the roll center height will be located at the virtual intersection of the two angled links. From a practical standpoint, with this design, you want to get this as low as possible. The Morrison designs put the upper, angled links at the height of the axle housing, which is better than most such designs which put brackets on top of the housing (unacceptable, IMO). Even better, as suggested by Herb Adams, is to make the lower links the angled pair, but this is more difficult to pull off from a structural and packaging standpoint.

Side View Swing Arm and Roll Steer: Viewing the suspension from the side, imagine extending the upper and lower links until they intersect in space. The line from this point to the center of the axle is the SVSA. The angle that this SVSA forms with the roll axis is important, because it determines whether you will have roll understeer, oversteer, neutral steer. If the SVSA is angled upward toward the front, you will have roll oversteer, which will make your car unpredictable and twitchy on turn-in. Some amount of roll understeer is generally considered desireable, but there are tradeoffs between achieving this and keeping the instant center higher to get more anti-squat. Also, keep in mind that the shorter the SVSA is, the more likely you are to suffer from brake hop.

Instant Center and Anti-Squat: The intersection of the upper and lower links in the side view, as described above, is the instant center. Draw a line from the point of the rear contact patch through this instant center, and find the intersection point with a horizontal line at the height of the center of gravity of the car. If this intersection point occurs forward of the front contact patch, you have less than 100% anti-squat, if it occurs between the contact patches, you have more than 100% anti-squat. Some amount of anti-squat is desirable, to help the car hook up on acceleration out of the corners. Just how much you want is debated, but if you can get close to 100% AS while still having roll understeer, you're doing pretty well.

Link Length: The shorter the links are, the more all of these parameters will change as the suspension moves, and the greater the chance that the suspension will start to bind up to a significant degree. From a practical standpoint, it's hard to have links that are too long.

Getting the optimum balance of all these parameters - even knowing what the optimum balance is, and what it feels like to the driver - is what makes suspension design hard. Build some adjustability in, for sure.

exwestracer

12-24-2010, 01:13 PM

All good basic information...
Personally, I would stay away from the "Adams" upside-down version in a high-horsepower, high traction car. Nothing wrong with the geometry, just remember that the lower links are pushing the car forward as well. Having them form the triangle can lead to the rear axle housing trying to do some weird things when you really apply some torque to it.

wedged

12-24-2010, 01:56 PM

not that I had any plans of doing anything like this, but what do you think ?

http://www.jimmeyerracing.com/pickup_gasser_rear_subframe.html

http://www.jimmeyerracing.com/images/gasser_rear_subframe_7463_sm.jpg

http://www.jimmeyerracing.com/images/gasser_rear_subframe_7475_sm.jpg

"The Jim Meyer Racing Products adjustable low-roll-center Panhard bar, that mounts behind the rear axle housing, is also parallel with the centerline of the housing and uses the same multi-hole bracket at the housing that holds the shockwave air spring or coilover shocks. This allows you to tune the track bar, up-or-down at the housing, for the handling you like best. The front swivel, at the forward thru-frame crossmember, allows the entire housing, suspension and Panhard bar to stay level with the pavement while the body and chassis rolls around corners and during launching off the line. Handling and cornering will be vastly improved with our thru-frame antisway bar and Low Roll-Center Panhard bar and a set of ShockWave Air springs. "

I can't comprehend how the bold part is physically possible.

Motorcitydak

12-24-2010, 08:31 PM

What about a satchell link? 4 bar system, straight uppers and triangulated lower links, no track bar to deal with. Gives you a really nice and low roll center and easy packaging seeing your predicament.

wedged

12-26-2010, 05:27 AM

"The Jim Meyer Racing Products adjustable low-roll-center Panhard bar, that mounts behind the rear axle housing, is also parallel with the centerline of the housing "

I just realized that there must be some new definition of "parallel" that I have not found yet.

I don't think that the satchell link has any packaging advantage over the traditional triangulated 4 link in my situation, but feel free to add ideas. So far there's a good amount of info here for applications that aren't restricted by stock sheet metal.

ccracin

12-26-2010, 09:13 AM

Treat this design like the sun. If you must look at it, look very quickly and then turn away even quicker!

wedged

12-26-2010, 09:54 AM

:rofl:

wedged

01-11-2011, 11:57 AM

over the last couple of days I ordered the parts for the triangulated four link rear suspension.

I've got 4 of these coming for the axle end of the links:

http://www.trail-gear.com/images/2008-1576-225.jpg

There's a set of these on their way:

http://www.swracecars.com/store/images/cart/40-223.JPG

And also some DOM tube to make the bars and bushing sleeves for the frame end of the bars and an assortment of laser cut mounting tabs.

wedged

01-22-2011, 04:24 PM

Most of the parts I ordered for the rear suspension showed up (pics in the build thread (http://www.lateral-g.net/forums/showthread.php4?t=21869&page=8)) . I did some mock up and measuring and then messed with my CAD drawing. In the drawing the center of the rod ends are aligned with the centerline of the axle as viewed from the side. The center of the upper link is 8.25" above the CL of the axle and the center of the lower link is 4" below. With a lower link length of 30",the effective length of the upper links at 28". The lower link is drawn parallel to the ground. I ended up with an instant center of 99.5" in front of the axle centerline. The wheel base is 116".

good ? bad ? comments ? I'm all ears.

Bryce

01-22-2011, 05:39 PM

You probably have a really low anitsquat percentage. So that might be something to consider.

wedged

01-22-2011, 06:12 PM

please explain a bit more. I know enough about this to get myself in trouble.

wedged

01-23-2011, 06:12 AM

I found this:

"The instant center is found by extending the lines through the pivot points until they intersect. From there, anti squat is found by drawing a line from the IC to the center of the tire at the ground. Where that line crosses the center of gravity line it creates our measuring point ‘A’. The percentage of the line from the ground to our intersect point is the percentage of anti squat."

Right now I have no idea where my center of gravity will be. I'm guessing it will be further back than a stock pick up truck and maybe slightly lower.

From a Car Craft article:

vehicles have a specific point around which the entire car will balance called the center of gravity (CG). For most domestic front-engine, rear-drive cars, the CG is generally located forward of the mid-point of the car at around camshaft height off the ground. While all rear suspensions pivot around a given point, this is not necessarily the point at which the rear suspension applies power or lift. Suspension engineers call this lift point the instant center (IC). Different suspensions place this IC at different positions in the car. Because suspension components tend to shift as the body lifts or squats, this position is dynamic, meaning that it moves as the car pitches or rolls. One definition of IC is the unseen center of an arc created by the moving suspension links. The simplest instant center is a drag race ladder bar. The forward mounting point for the ladder bar where it hooks to the chassis also happens to be its instant center. With other rear-suspension designs, the instant center is an imaginary point in space.

Kevin Gertgen's Performance Trends has created a drag race four-link computer simulation program called 4 Link that offers pictures that tell the story much easier. If you look at the illustration, you'll notice a pair of dotted lines that extend from the lines drawn by the two upper control arms and the two lower control arms. The intersection point of those two lines is called the instant center. The 4 Link program allows you to reposition the IC by moving the mounting points of the upper and lower control arms. Also notice the dotted line that extends from the rear-tire contact point forward at an angle. This line intersects a point created by the intersection of the horizontal CG line with a vertical line drawn through the front spindle. This angled line is called the 100 percent antisquat line, or sometimes called the neutral line.

By changing the location of the upper and lower four-link bars, you can move the IC location either above, directly on, or below that 100 percent antisquat line. When the IC is positioned below that 100 percent antisquat line, the rear of the car will squat on acceleration and "hit" the tires relatively softly. When the IC is positioned above the 100 percent antisquat line, the rear of the car will tend to rise on acceleration and "hit" the tires harder. Obviously, if the IC is placed directly on the 100 percent line, the rear will remain neutral.

This explanation holds true for all rear-drive cars, but there is plenty of confusion around the location of the instant center with different suspension systems. For example, with leaf-spring cars, the IC is the front spring eyes, but with ladder bars, the IC is the front pivot point. Factory four-link cars are determined exactly the same way as drag race four-link systems. If you extend imaginary lines forward on a factory four-link rear suspension, the IC generally falls in front of the car, well below the 100 percent antisquat line. This is why all factory four-link cars squat on acceleration. By installing the Lakewood anti-hop bars (for example), this kit raises the rear locating point of the upper control arms roughly 2 inches. This shortens the IC length and also places it above the 100 percent antisquat line, which now helps plant the rear tires. "

I guess if I make the bottom bar to angle upward from the rear to to front mount point and reduce the angle of the upper bar the same amount, that will increase the anti squat ?

Roadbuster

01-23-2011, 07:49 AM

For calculations and simple explanation:
Schope's site (http://www.racetec.cc/shope/index.htm) has good instructions, illustrations and lets you plug in the numbers.

Jon

Bryce

01-23-2011, 08:00 AM

To calculate the A/S you need to know the height of the CG.

There are probably pictures online on how to calculate it but I will try to explain it.

Draw a vertical line at the front tire contact patch.
Draw a horizontal line at the CG height and intersect the vertical line you just drew.
Now draw a line from this intersection point to the contact patch of the rear tire. You should have an upward slopping line from the back to the front.
This line is your 100% anitsquat line. If your IC is on the line you have 100%, below the line is less and about is more than 100%.

If you want to have a street/autocross car I would keep the LCA parrallel to the ground. This keeps you roll steer neautral.

wedged

01-23-2011, 08:25 AM

If i keep the lower parallel to the ground, then i would need a steeper angle on the upper bar. i think. :willy:

Bryce

01-23-2011, 10:06 AM

If i keep the lower parallel to the ground, then i would need a steeper angle on the upper bar. i think. :willy:

Yes, if you wanted a higher A/S. For a street car build it to 50 to 100% and make it adjustable. For a drag car I would build it from 90 to 150%. Leaf spring cars have well over 100% but have wheel hop issues, where they cant put the power down. My 65 drag mustang has leafs and slapper bars. I lauch with the front wheels off the ground and I only have 300 hp.

wedged

01-23-2011, 11:36 AM

I just spent some time messing with the CAD drawing. I dropped the upper forward mount point a bit and ended up with the instant center at 50". I guesstimated where the center of gravity would be, then drew the anti squat line. What resulted was interesting. The instant center was directly on the 100% line. :_paranoid

Then i went over to the mocked up truck and fired up the FARO ... I wish. I grabbed a tape and held in place to see about where the front pivots points would be. The upper would be outside of the inner edge of the rear tires, making the frame kind of interesting. It would either need to stay low and pass under the upper bar or go really high over the bar. If I shortened the upper bar to about 18" OAL, it could land on the frame rail with the frame a width that would fit between the tires. Of course the lower bar would then be about 20" long. I'm going to think this over a bit before I make a decision on what way to go.

64pontiac

01-23-2011, 11:50 AM

Not that I know as much as some on suspension design, but one thing I have found is that IF you have to go with a shorter upper link, you can overcome crazy pinion angle changes and binding by making the attachment point on the housing farther back from the axle centerline than the lowers. It seems when I am playing around with suspension worksheets that a similar ratio as the arm length helps. My 3 link on my 64 has a super short upper link, but is mounted farther back from axle centerline and I have NO pinion angle change over the whole sweep, and Im on bags. I also punched in everythign into the suspension calculator, and I still have acceptable antisquat and roll centers, which are all adjustable.

If you are going for Air ride later, and have a narrow frame, huge rollers, and tight fender clearance stay away from a panhard if at all possible. you will probably touch the tire to the fender on full air-out otherwise.

A watts linkage or sliding wishbone are ideal, as a triangulated 4 link works great for coilovers but tends to bind on air ride systems.

I know you probably have figured everything out, but just wanted to chip in my half cent.