The Roll Centers (RC), are the foundation of the car, and the entire setup is built around them.
Changing the RC balance will require you to re-work the setup around the new foundation.
High RC: A high RC will make the car feel "on the track". There is a jacking effect, which raises the car up as it corners. Entering a corner too fast can cause the car to "jack up" and flip over.
Cornering too fast on power can cause the car to "jack up" and flip over. The benefit of a high RC is that the car has more initial grip, and a high peak of traction, so on loose tracks you can gain response and speed with a higher RC.
Low RC: A low RC will make the car feel "in the track". There is a low jacking effect, or even one pushing the car chassis down into the track. When you enter a corner too fast, or you corner on power too fast, the car will roll downwards towards the track, making it feel "in the track", and safe to drive. The downside is that you lack initial grip, and have more overall grip. Meaning you have less response, but a safer smoother feel. On low grip this can make the car too lazy, or cause it to fishtail when accelerating.
Upper Link Angle: Changing the angle of the upper links in relation to your lower arm is a good way to adjust the balance of your RCs.
A larger angle (lower on tower and/or higher on hub) raises the RC, a smaller angle approaching parallell (higher on tower and/or lower on hub) lowers the RC. A higher angle has more initial grip, and is more on the track, and a smaller angle has more overall grip, and is more in the track.
Upper Link Length: Changing the upper link length has a minor change to RC, and it is better to think of the link length as a way to tune the speed at which the car responds, with short links being more responsive (faster roll and load transfer) , and long links being more calm (slower roll and load transfer). You use link length to fine tune response speed, after setting the RCs with upper link angle and lower arm height on inside.
Lower Arm Height: Changing the height of the lower arm is a good way to adjust the balance of your RCs. A higher arm results in a higher RC, a lower arm results in a lower RC. A higher arm has more initial grip, and is more on the track. A lower arm has more overall grip, and is more in the track.
Axle Height: Axle height changes the RC, but the best way to think about it is to remember that a lower axle height has more initial grip, and a higher axle height has more overall grip. You use axle height to fine tune initial vs overall grip after you set your RCs with the upper link angle and lower arm height on inside.
Upper Arm Height (keeping same angle): Changing the upper link height has a minor effect on RC, and the best way to think about it is to remember that a lower link height will have more initial grip, and a higher link height will have more overall grip. You fine tune the initial vs overall grip with link height, after you have set your RCs with the upper link angle and lower arm height on inside.
Balancing the front to rear RC relationship is important. There is a general rule of thumb that you can follow:
Low Front - High Rear: The Car will drive in a way where the front end has smooth initial steering, good steering mid corner,
natural rotation, and as you get on power, the rear end grips and supports the car, while the front end pushes slightly. This setup tends to be easier to drive because the initial steering is smooth, the risk of the car flipping over is lower, and as you get on power the rear grips.
High Front - Low Rear: The car will drive in a way where the front end has good response into the corner, less steering mid corner,
but the car rotates due to the rear rolling, and as you get on power, you have to be more careful not to overload the rear as it is soft, your car will want to keep turning out of the corner, and on a loose track the rear can start to fishtail. This setup tends to be harder to drive, but it can be very fast because it is responsive into corners, and steers a lot mid to exit.
Whichever direction you choose, you then adjust the initial vs overall grip and "timing" of load transfer on each end around the RC balance with all the setup features of the car.
You mainly set the RC balance by setting upper link angle and lower arm height on the inside front and rear.
You then adjust initial vs overall grip with link length and axle height.
Once you have a good balance, by adjusting both front and rear RCs together, by raising or lowering links or arms front and rear, you can
adjust the on/in the track feel without affecting the balance too much.
The front upper link is used to adjust the on the track, or in the track feel (angle), as well as the response of the car (length or angle).
The recommended starting point is middle on tower, long top on hub. We almost always run long on hub. You would only go shorter there if your car is good,
and you just want a bit more response from the car.
On the tower you would run the top hole if you want the car to be more in the track, and less likely to flip over, and you want smoother initial steering response.
Always start with your link high on the hub (and middle or top on tower, depending on your preference). This will be the smoothest setting with best overall grip.
If you then want more initial grip, and steering into the corners, you can keep the same in/on the track feel by keeping the same angle, and lowering the link
inside and outside.
We do not recomend running the lowest hole on the tower and the highest hole on the hub. Only run the lowest hole on the tower if you are running the low hole on the hub. (hub with insert)
We do not recomend running the highest hole on the tower and the lowest hole on the hub. Only run the highest hole on the tower if you are running the high hole on the hub. (hub with insert)
The rear upper link is used to adjust the on the track, or in the track feel (angle), as well as the response of the car (length or angle).
The recommended starting point is middle on tower, long top on hub. (3mm height shims)
The length adjustment on the hub is a common setup change, as it greatly
affects handling:
On the tower you would run the top hole if you want the car to be more in the track, and less likely to flip over, and you want more mid corner grip.
Always start with your link high on the hub (3mm height shims) (and middle or top on tower, depending on your preference).
This will be the smoothest setting with best overall grip.
If you then want more initial grip, which allows for good rear grip on corner entry, reduction in grip mid corner, allowing for more off power rotation, and then more grip
again as you get on power, you can keep the same in/on the track feel by keeping the same angle, and lowering the link inside and outside.
We do not recomend running the lowest hole on the tower and the highest hole on the hub except if you are running on a smooth, loose track.
We do not recomend running the highest hole on the tower and the lowest hole on the hub. Only run the highest hole on the tower if you are running the high or middle hole on the hub.
The starting setup is middle for both links on the towers, and top long on both hubs.
To maintain the same balance, but change in/on the track feel, raise or lower both links on tower together.
Raise links on tower for in the track and more overall grip. Specially good on high grip or edgy tracks.
Lower links on tower for on the track and more initial grip. Specially good on smooth loose tracks.
To change the RC balance, raise or lower only one end, or change both in opposite directions.
The end with the less angled link and lower RC, will have less initial grip, so less grip entering a corner, more grip mid corner and then won't grip as much as you get on power and accelerate out of a corner. That end of the car will also feel softer and
more in the track, and will handle bumps better.
The end with a more angled link and higher RC, will have more initial grip, so more grip entering a corner, a loss of grip mid corner,
and then it grips more again as you get on power and accelerate out of a corner. That end of the car will also feel stiffer and
more on the track, and will catch bumps more.
The higher the grip, the less angle you want to run on your links, and the higher link height overall you want.
On lower grip it is a question of preference, running the same links as on high grip, or more angled in order
to generate more initial grip.
Invisible Speed RC video:
https://www.youtube.com/watch?v=aG4KJ5ohsOo&t=299s