jerry gollnick

Does anyone know how to calculate or find the roll center on a C2/# rear suspension?

Bill Dearborn

The GM Performance Parts division in the 70s used to have a book that completely covered preparing a C2/C3 for racing. They had all of the information for calculating roll center and other suspension data points. Mine is long gone but you may be able to find one by searching on the web.

Bill

96CollectorSport

I believe it was called the Chevy Power Book - like this

http://www.duntovmotors.com/Corvette...wer%20Book.pdf

Bill Dearborn

That is it. Just need the section on suspension design and adjustment.

I always hoped they would update the book to cover the C4s but even into the early C4 era they only had the C2/C3 section and after that they focused on Camaro's only.

Bill

jerry gollnick

I have the Chevy Power publications. All of them, there is a section on theorectical suspension configurations and calculations. None of these cover the CORVETTE rear suspension design. Some may think it infers a solution but the trailing arm interaction with the camber and half shaft arcs adds an element that is very different from a traditional rear suspension design. I'm looking for anyone who has information on C2/C3 Corvette rear suspension roll center calculation. Chevy Power is not it. If you have something else please send it.

69autoXr

I googled "roll center calculation trailing arm suspension" and one of the results was the link below, a book called "How to Make Your Car Handle". I couldn't find an exact configuration match for the C2/C3 IRS so I started with the "semi trailing arm" suspension shown on page 38 and went from there.

The pivot axis I think would be a line drawn from the trailing arm pivot the half shaft inner u-joint, which puts the instantaneous center also at the inner u-joint. The roll center is then found by drawing lines from the (my) instantaneous centers to the center of the tire contact patches, putting the roll center slightly above the horizontal plane of the inner u-joints.

I don't know if it's right or not, but it's my attempt. I drew a non-scaled diagram to help me visualize it, and the result doesn't seem unreasonable to me.

http://books.google.com/books?id=cr4...ension&f=false

jerry gollnick

This approach makes more sence to me than any of the others i've seen tried. This would say lowering the differential or raising the trailing arm pivot point would lower the roll center. Do you agree?

SuperL98

Had this link to a 1963 SAE paper on the corvette, does it help?

http://www.web-cars.com/corvette/196...per.php?page=8

jerry gollnick

This does help, thank you. The problem both of these sources have is that they are trying to meodel a system that has interactions with the trailing arm that are not discussed in the SAE paper. In Millikens "Race Car Vehicle Dynamics" on page 639 we see an attmt to tie the trailing arm to the Instantaneous roll center but no example calculations are given that actually use the effect of the trailing arm.
If you take a pencil and straigtedge and start drawing intersecting lines using the SAE model you find the camber bracket location has the most powerful effect on the roll center. It's really easy to move it around and get odd roll couple linking to the front roll center. ( I've made this mistake)
I have been moving components around on the race car and as you would expect it's all a compromise. I suspect GM felt the effect of the trainling arm on instantaneous roll center was negligable or they jhust got it wrong. I've seen this in the Rochester Fuel injection SAE paper. When I did the tests things were just omited or glossed over. It was 60 years ago and these aare publich documents so maybe they didn't show all they know.
I really appreciate the ideas and input from this thread. Oh well, back to the race shop. It's time to throttle the engineer in me and pick a setup and do some testing. Jerry

DaveL82

My car has similar roll center to stock as the pickup points are in the same location (verticle) . My car now runs an upper and lower control arm type setup which ended up being a hybrid of systems used for GT1/IMSA cars in the late 70's. My primary focus was to reduce tow steer caused by the single fixed point trailing arm.

My next step is review roll center over the winter. My lower control arms have tow pickup points available but did this mainly for camber gain adjustability (stock location and 3/4" lower inner pickup points)

Dave

jerry gollnick

You can get toe change in bump down to less than .010 if your careful with setup. In droop it's tougher but less important.