Yup I've been busy. It wouldn't look good to a new boss if I take the time during the workday to type up something as long as this is going to become! So here goes...

When it comes to camber link location, you need to remember that any change in length or position affects roll centers. Roll center is not a static location in space. It changes with suspension movement. You can change the rate at which roll centers change meaning you could have 2 setups with the same roll center at ride height but entirely different roll centers at either extreme of travel. If you do any reading about roll centers and how to determine your instant center then it shouldn't be hard to figure out where this theoretical point is for any amount of suspension movement.

I personally don't like to think of roll centers as a point in space that the car rotates around because that very concept is quite irrelevant. Nevertheless we use the term roll centers anyways. I think about changes in the link locations in a more relevant way. Some refer to this as camber gain. This is a byproduct of roll centers and ultimately tells you if yours is higher or low. I think of upper link length and location in terms of roll resistance or stiffness as that's what we are using it to control.

Here's an example of something that happened to me this week. My car had pretty nice handling with the links where they worked very well. I ended up changing the rear links over to a captured link setup because I'm tired of ball cups popping off. Due to clearance reasons I ended up moving the rear link locations. However I ended up lowering the rear roll centers quite a bit. This is visually seen as less camber gain with suspension compression. The effect was a car that understeers heavily. The rear end seems soft in corners and the inside front wheel comes off the ground. You are much faster with all your wheels on the ground! In corners it behaves as if the rear shocks need to be stiffened quite a bit. Don't do this! Shocks and springs were done to control bumps and jumps, not cornering ability! By raising the rear roll center I can add rear roll stiffness in corner which will keep the front end down and will increase cornering power. I just need to fix this. If I used the rear shocks to take care of this, now the car would handle horribly everywhere else.

Now it seems logical that raising the instant roll center to gain roll resistance is the obvious choice. It is certainly the easy thing to do. However this is where learning how to read your tires comes in handy. You see, your tires tell you what is going on where it counts, where the tread touches the track. With the higher roll centers I was getting greater wear on the inner half of the face of the tread and far less on the outer half. A roll center that is too low will have the exact opposite result. In a perfect world you would be using all of your available tread. With my new low roll center and hence low roll resistance, a byproduct is that my tire wear is now quite even across the face of the tread. So do I raise the roll center and potentially lose some performance from not using all of my tire or do I keep the roll center low but lose cornering ability from not having enough rear roll rate stiffness? The answer is neither.

This is where another trick comes in. It's called a sway bar. Yes they do have a purpose and no they aren't necessarily always needed. I can clearly tell that my tires like my low roll center setup but rear roll stiffness prefers the higher roll center. By adding a sway bar I can have both. How thick of a sway bar? The simple answer is as thin of one that you can get away with and still get the results that you desire. The thicker the sway bar gets, the more and more the suspension behaves less and less like an independent suspension and more like a solid axle. This is an exaggeration but hopefully the point is made. The front of my car shows fairly even tire wear across the tread with the roll center that I have set there so no changes are made. A sway bar is sometimes needed at only one end, sometimes needed at both ends, or sometimes is not needed at all. If I were going only off of performance I'd be tempted to set the rear roll center high and be done with it. By learning how to read my tires, I can see the solution plain as day. It's obvious.

Now back to those upper links. The question was asked earlier what happens if you have the exact same length links but move them over either inward or outwards. Even if you keep the same length and they are always pointed the same with suspension movement, you are still altering your roll centers. By moving the links outwards but keeping them the same length, you are slightly raising your roll center but you are doing it evenly across the suspension range of motion. It is always going to be higher an even amount across the range of motion.

Sometimes you want to alter the roll centers evenly across the entire range of suspension travel. Other times you may want it low at some places and higher at others. Perhaps you want the stability of a low roll center during a long smooth straight but have very tight corners that require a greater amount of roll stiffness. In this case you'd want to shorten your upper links rather than merely move them over. Only you can tell for sure based on how your car handles and what your tires say.