rear suspension design help needed

[wedged]

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 :

Originally Posted by PTAddict

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]

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]

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

http://www.jimmeyerracing.com/pickup..._subframe.html





"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]

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]

Originally Posted by wedged

"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]

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

[wedged]

[wedged]

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:



There's a set of these on their way:



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]

Most of the parts I ordered for the rear suspension showed up (pics in the build thread) . 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]

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