Roll Center is perhaps the most complicated and hard to understand concept of chassis setup. Roll
Center is adjusted with Camber Links by changing camber link locations and lengths. I highly suggest
leaving Camber Link and Roll Center adjustments to the expert racers with a firm grasp on chassis setup
and handling. Roll Centers are difficult to explain even when using lots of drawings and diagrams. I am
going to do my best to teach you the basics, without getting overly complicated and getting you
completely lost. Roll Center basically describes the relationship between the upper and lower arm of the
suspension. The lower arm would be the A-Arm, while the upper arm would be the turnbuckle.
What is Roll Center?
Roll Center (RC) is the point of which the chassis rolls while cornering. Your chassis will have a front roll
center, and a rear roll center. RC is something that we can change on the chassis by using various chassis
adjustments. (Further details later)If you would rather not get too complicated about RC, please feel
free to skip the next 2 paragraphs.
How do you determine where the Roll Center is?
Without getting too complicated, RC is figured by taking measurements and drawing a diagram based on
data compiled from you chassis such as pivot locations of upper and lower arms and the center of the
contact patch of the tire. Calculating RC is a pretty complicated and tricky process involving many
factors, however the information obtained can be quite helpful to a racer trying to fine tune their
suspension. For a basic understanding of RC, look at the rear of your chassis, at race ready chassis
height. Now draw an imaginary line between the outer and inner hinge pins on your LR A-Arm. Next,
draw a similar imaginary line between the inner and outer camber link mounts on the LR A-Arm. Where
these lines intersect is known as your Instant Center (IC). Now draw a line from the IC to the center of
the LR Tire’s Tread Width where it contacts the track surface. The point that this line crosses the
centerline of the car is your RC. This can be further complicated on Dirt Oval chassis by offset chassis and
by setups utilizing staggered camber link locations and angles.
What is Center of Gravity?
Center of Gravity (CG) is a generalization for the center of mass. The CG is the point where a chassis’
weight can be balanced, and will stay there until the application of an external source of energy. CG can
be changed by physically changing the location of mass/weight on the chassis.
Roll Center and Center of Gravity
Dirt Oval Chassis ALWAYS have a RC that is much lower than the CG. This is important to know, so any
RC adjustment we make will make a change in a particular direction.
Moment Arm
The Moment Arm is the imaginary line connecting the RC and CG. The length and subsequent leverage
of the Moment Arm is the controlling factor of chassis roll while cornering. All of this calculating is done
so we can find and change the leverage of the Moment Arm and how it acts on the CG during cornering.
Raising Roll Center
Raising the RC moves it closer to the CG, which results in less leverage of the Moment Arm. Less
leverage (shorter moment arm) results in less chassis roll during cornering.
Lowering Roll Center
Lowering the RC moves it farther away from the CG, which results in more leverage of the Moment Arm.
More Leverage (longer moment arm) results in more chassis roll during cornering.
Roll Center Cliff Notes
Adjustments That Raise Roll Center
- Lowering the inner camber link mounts.
- Raising the outer camber link mounts.
- Raising the suspension mount relative to the chassis.
Adjustments That Lower Roll Center
- Raising the inner camber link mounts.
- Lowering the outer camber link mounts.
- Lowering the suspension mount relative to the chassis.
Camber Links
Now that we have covered what the various Camber Link angles do for us regarding chassis roll and
controlling weight transfer, let’s get into what various camber link lengths do for us. Remember, your
lower A-Arms are an acting force of your suspension geometry, and in general we are figuring the effects
of the Upper Link (Camber Link) on the lower link (A-Arm).
Neutral Camber Links
When your car has equal length upper and lower links that are parallel to one another, this is called
Neutral Camber Links. This will be the most neutral handling, easy driving, and predictable setup. All
MurfDogg Chassis are designed to have the ability to run Neutral Camber Links. We run Neutral Links
95% of the time, and only stray from this setup in extreme conditions (Extreme Low-Grip or Extreme
High Bite).
Camber Link Lengths
- Shorter Links typically result in more camber change. More Camber Change equals more initial weight
transfer to that corner. - A short link that is parallel to the lower arm will have a very low RC, which will initially cause the
chassis to roll easily, but a longer link at the same angle will have increased chassis roll into the corner.
This is because the as the car leans into the corner, the RC of the longer link actually will get to a point
that is lower than the RC of the shorter link. Basically, the longer parallel link will have less initial roll, but
will roll more as you get farther into the roll than the short link which provides more initial roll. - Longer Links typically result in less camber change. Less Camber Change equals less initial weight
transfer to that corner. - A long link that is parallel to the lower arm will have a slightly higher roll center during
Camber Link Cliff Notes - Higher Inner Camber Link Pivot = More Chassis Roll
- Lower Inner Camber Link Pivot = Less Chassis Roll
- Lower Bite Tracks = More desired chassis roll to create more traction.
- Higher Bite Tracks = Less desired chassis roll to control bite and increase steering.
Chassis Tuning 101
Matt Murphy’s Dirt Oval Chassis Tuning Guide