Few questions about suspension design

[Chris1985]

Couple of questions, also please redirect me if I'm off, I'm struggling to get a better grasp of suspension kinematics.

1. I was wondering, is there an optimum amount of camber gain desired? The way I understand it is a little bit of gain is good in order to rotate the outside wheel to increase tire contact patch. But at what point is it affecting the roll center too much?

2. Where do you place a roll center? If it's above ground, you can get jacking forces, but are they necessarily bad? since the car is being pushed up, that means the tires are being pushed down. If it's below ground the car will tend to squat, which I can see would lower the center of gravity... is this the only reason the roll center is sometimes placed under ground due to the CG?

3. And finally, does anyone know of a good animation of roll center migration?

[Big Mo]

As far as "animation" goes, I think the closest program to suit your needs is WinGeo.

As for your other questions, they seem a bit vague. Ultimately, making the design decision of constricting roll-center migration versus maximum camber gain is a compromise you have to make based on your car and ideas.

[terra_dactile]

chris,
Get the university priced version of Optimumk, or even down load the demo to play around with the ideas you have been discussing with pitch and roll axis migration.Check out their website www.optimumg.com (http://www.optimumg.com) and all fo your otions are explained.

Jude Berthault
ETS FSAE 2003-2009
Alumni

[exFSAE]

Preface - I despise the word "optimum."

1 - Depends on you and your tires. There's no clear cut solution, which is why I hate the word "optimum" ! Do you want to focus more on cornering grip? Longitudinal? How camber sensitive are the tires?

2 - Up to you as well. Jacking force isn't necessarily bad, you'll have to see what kind of magnitude of jacking you'd get at RC's at say 1, 2, 3" off the ground. Bear in mind RC's change a lot. Drop ride height, and RC's drop. Hit the brakes, and one RC goes down while the other pops up, etc.

3 - For kinematic RC migration? There are probably a lot. OptimumK, SusProg3d.. hell you can even draw it in Solidworks.

[rafasosa]

As for a really basic way to see how your GC moves in bump and roll Carrol Smith gives a way to model a car in one of his book (I think it is Tune To Win) It'll give you a basic knowladge of how it moves.
Also if you want something more approached to a simulation you could use Lotus or Optimunk to analize it's movements.