Three-link, need some suggestions

[Exhausted]

Matty, I am building my own 3 link, was working on the crossmeber to mount the upper link tonight before I signed up to this site. I can't give you all the technical ifo, you may be asking, but my friend that is explaining as I build, (lol) does understand, and I would be willing to ask and tell you anything you need to know to build your own

[Exhausted]

also, I am using my stock leaf spring front mounting points for my lower links, 9" ford rearend, DSE minitubs, DSE Sub Frame connectors, Not sure on my coilovers, just yet, I will buy Heim Joints and rods, but I will fabricate most of everything else. (1971 Nova)

[matty b]

id like to see some pics if you wanna put em up. You using the stock rails or did you go ahead and put in new rails and tub it? I know our procedures will be way different but luckily I think mine will be the easier way.

[BillyShope]

Matty, I am building my own 3 link, was working on the crossmeber to mount the upper link tonight before I signed up to this site. I can't give you all the technical ifo, you may be asking, but my friend that is explaining as I build, (lol) does understand, and I would be willing to ask and tell you anything you need to know to build your own

Are you offsetting the odd link? If you offset it correctly, you can dynamically cancel the effect of driveshaft torque on rear wheel loading. In other words, your rear tires can be equally loaded during launch with any value of driveshaft torque.

See Page 18 of my site for setup information. Check out Pages 4, 5, and 6 for a method to verify your setup.

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

[baggins]

what is more advantageous... parallel lower links or triangulated???

[matty b]

i believe that angled lower bars are better, why and how much I dunno but I read its better

[BillyShope]

what is more advantageous... parallel lower links or triangulated???

As usual, there's no correct answer. It depends on your application. Angulation of trailing links (either top or bottom) is usually done to avoid the need for a Panhard rod to take lateral loads while cornering. It's very difficult, however, to provide convenient adjustment with triangulated links. In other words, you're usually stuck with the percent anti-squat of the original setup. With links that are parallel to the long axis of the car, you need a Panhard, but, on the other hand, it's relatively easy to provide adjustment.

And, of course, there's the matter of packaging. With any given car, one setup is going to be easier to install than the other.

So, it comes down to what you want to do with the car. If it's only going to see street duty, there's really no reason for tinkering with the percent anti-squat and the triangulated setup will be quite adequate. But, if it's essentially a dragstrip car, you probably will appreciate the adjustment and you'll go with the parallel arrangement.

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

[Exhausted]

In reference to BillyShope's question, My upper link will be centered give or take an inch or two. I'm a drag racer at heart, I know a 4 link, would be better, but My car will very seldom see the track, It's just a car to cruise short distances, I plan on using mid 80's camaro rear bucket seats, mainly for looks not for function. Another friend of mine is building a 3 link, it's almost done, with the upper link, set about 4 inches toward the center from the right lower link. But it is mainly a drag car, maybe burgers on Sunday afternoon. I'll take a look at your sitght, thanks for the info.

[Exhausted]

Mattyb, I thought long and hard about mini tubs apposed to gutting the car, building new rails, and buying stamped tubs from jegs or summit, the mini's I think are over priced, but hey that guy needs to make a living to. They look great. I am not gonna go real wide for my rear wheels, thinking about 17x9.5 maybe 10's, I have 16x8 Torque Thrust 2's with a 5-1/4" back spacing, front and rear, on the car now. So, keeping the stock frame rails, going with mini tubs.

[Norm Peterson]

what is more advantageous... parallel lower links or triangulated???

It's something of a compromise either way. A little plan view convergence of the lowers makes the axle roll steer vary less with changes in rear ride height (a good thing for handling 'predictability'). But converging lowers may force you to choose a slightly higher roll center than might be do-able with parallel LCAs (depending on their side view inclinations, among other things).


Norm

[matty b]

Mattyb, I thought long and hard about mini tubs apposed to gutting the car, building new rails, and buying stamped tubs from jegs or summit, the mini's I think are over priced, but hey that guy needs to make a living to. They look great. I am not gonna go real wide for my rear wheels, thinking about 17x9.5 maybe 10's, I have 16x8 Torque Thrust 2's with a 5-1/4" back spacing, front and rear, on the car now. So, keeping the stock frame rails, going with mini tubs.

im looking at alstons catalog at the moment and I think Im gonna call them about a rear clip. A clean sheet of paper is probably gonna work the best as I can fit the tire I want, and not have to really compromise on anything. Damn this is snowballing into something I didnt really expect to do but a deep dish 335 sounds awfully tasty.

[baggins]

so how would you go about finding what the best angle to put the lower arms at... packaging doesnt really come into play, other than cleanliness, because all i have done so far is bare rails and a mid crossmember

[Norm Peterson]

It's a process of iteration, where you're trying to get the roll center at some general height and axle roll steer and anti-squat to within some ranges, Best to work with some sort of software or at least a spreadsheet, because you'll perhaps start with a roll center height and either roll steer or anti-squat and see what the unspecified one ends up at. And you'll want to see how all of these vary as ride height is varied (at least).

Conventional wisdom seems to put anti-squat in the 50% range for a road course oriented car and 100% for a street/strip car. Roll steer numbers in the 3%-ish ballpark (as a vehicle roll understeer effect) for a cornering sort of car are reasonable, maybe a little less for serious competition.

Or you can start with a known setup (or a reasonable, perhaps scaled-off-a-picture guess at one) and iterate from there.


Norm

[baggins]

thanks Norm. man this whole suspension thing is pretty tough to grasp but slowly im adding a little more to my knowledge. thanks again

[35spline]

I am bringing this topic back to ask a few questions on what has already been stated. From a list things to optimize when desinging a 3-link

Originally Posted by jerome
vertical distance of link attachment from rearend centerline: as long as possible without touching ground when you get a flat tire.

What is the benifit of doing this verses doing just the opposite? I was thinking about maintaining ground clearance with the 3-link I am planning.

Here is a spreadsheet that captures what I have so far. I would really appreciate any suggestions to improve on what I have so far.

[jerome]

The longer the distance is from the rearend centerline to the link attachment, the less force the rearend will transfer into the links. When you accelerate, a rotational torque is created in the housing opposite of the rotation of the tires. The force created is the torque divided by the length of the lever arm (the distance we are talking about). If this distance is large, then the force created is small. This allows your link bars to not be ridiculously beefy. There is a limit to the benefit that this provides

I think a good ballpark for this distance is somewhere between 5 and 7 inches. Ground clearance is a good point, but the rearend attachments should probably be very close to the tires, so it is less of a problem. If you do 5 inches, your links will probably still be higher than the bottom of the rearend.

Hope that helps

Jerome

[35spline]

My lower links will be near the tires and out of the way but I was thinking more about the clearance at the frame end since the links converge at a 15 degree angle and are basically horizontal. As for the links I have 1.75" dia .120 DOM tube and the large Johnny Joints. I thought this would be strong enough for a 345/30/19 radial tire even on a high HP car.

Sorry I could not get my excel spreadsheet to load even when copied into a word doc. If someone could please send a pm on how to do this I will post the info. Here it is just pasted into the post (not good).


3 Link Calculator v1.0 - Vector-Based with Graphical Worksheet Add-In


Vehicle Specifications:






Wheelbase 108.0 in = Mess with these cells


Tire Diameter 27.00 in





Tire Rolling Radius 13.50 in Created 2004.06.17




Sprung Mass CG 'Z' 20.00 in by




Weight 3,400 lb Dan Barcroft




Suspension Geometry:


Geometry Summary:

Upper Link x y z
Anti-Squat 95.45 %
Frame End 36.00 -12.00 14.00 in Roll Axis Angle -0.66 degrees ( - roll understeer, + roll oversteer) Axle End 0.00 -12.00 21.00 in Roll Center Height 10.93 in
Lower Links x y

Instant Center X-Axis 56.57 in
Frame End 36.00 10.00 10.00 in Instant Center Z-Axis 10.00 in
Axle End 0.00 18.00 10.00 in



Pannhard Bar x y





Frame End -6.00 16.50 11.00 in



Axle End -6.00 -17.00 11.00 in






13.00

[BillyShope]

35spline, if you're concerned about ground clearance, I would recommend you go to symmetrical links on the top and the odd link below. Page 18 of my site will give you the necessary geometry for equal rear tire loading and 100% anti-squat.

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

[BillyShope]

Or, if you want to keep the symmetrical links on the bottom, you can move the rear mounting points forward and up. There's no requirement that the link mounting points be directly above or below the axle centerline.

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

[35spline]

Or, if you want to keep the symmetrical links on the bottom, you can move the rear mounting points forward and up. There's no requirement that the link mounting points be directly above or below the axle centerline.

Thanks, that's a good point. I finally got the rear housing under the car and set at ride height to see how everything would fit. It looks like I can maintain about 6 1/2" to 7" of ground clearance to the lowest point of my link brackets using Jerome's vertical spacing suggestion.