four-link suspension

[cmeyer7747]

I need some help designing a four-link rear suspension for a 70 Camaro. I’m not sure where to start with my analysis. I’m going to be driving the car on the street so I’m not trying to design a race car. I know that if I were designing a race car I would look at the track conditions in which I would be racing, i.e., turn radius. I’m not sure what driving situations I should be concerned with. Should I decide on a critical speed and design around that? I understand the kinematics of the four-link from reading Race Car Vehicle Dynamics by Millikin and Millikin and have constructed a 2-D drawing of the plan and side view for the suspension. I’m not sure how to figure out how much understeer I want to achieve from the rear geometry. Some insight into this would be helpful.

Chris

P.S. I’m also curious how to find specification on the car, like radius of gyration.

 

[GregLocock]

Critical speed should be considered but is unlikely to be of much concern for a street car.

Really you want a suspension that doesn't steer too much in any condition, and that generally tends to oversteer the axle (ie understeer the car), rather than the opposite. Of course to work this out you need to know what the front suspension is up to...

You also want to hold the wheels square to the road, or slight neg camber for the outboard wheel.

With a 4 link suspension your options are pretty limited. Start by laying out the longest lower arms you can sensibly package. In side view then adjust your upper arm length to give you antisquat.

In plan view angle your upper arms in to give you some steer.

Getting the radius of gyration is tricky - if you can find a figure for a similar sized car use that, or else build sa spreadsheet with all the components in and enter the centre of gravity and mass of each component, and an estimate of the component's radius of gyration, or if all else fails use Rzz=1/8*width+1/3*length. Doesn't Milliken give some guidelines?

There is a way of measuring it directly using a trifialr suspension, but it is not practical unless you have a 30 foot high gantry and a suitable platform.



Cheers

Greg Locock