| THE BASICS - DYNAMICS 2 |
| BODY ROLL AND LATERAL LOADING EXPLAINED |
| The simplest way to differentiate between the two is to note that body roll is the angular tilt of the sprung mass of the vehicle while loading is the amount of weight on the tires, which are part of the car's unsprung mass. |
| Body roll is controlled by the anti-roll bars and the spring/shock combination. How much roll resistance that is delegated to the ARBs (acronym) and how much to the springs/shocks is up to you as the tuner. Keep in mind, in regard to body roll, that the primary function of springs and shocks is not roll resistance. Springs and shocks are primarily responsible for tire compliance and vehicle responsiveness. |
| Lateral load transfer on the tires is controlled mainly by the ARBs, meanwhile the spring/shock combination does little to load the tires. This may sound surprising, but it makes perfect sense. Here's a quote: |
| "One of the most widespread misconceptions in racing is that the amount of load transfer taking place is directly related to chassisroll. Two opposing theories are prevalent: |
| 1- The car that rolls a lot transfers more load and so develops more cornering force. |
| 2- The car that is strongly restricted from rolling doesn't transfer as much weight and so develops more cornering force." |
| Carroll Smith - 'Tune To Win' - pg.36 |
| If you'd like to get further in-depth on the subject, I strongly encourage you to go out and pick up a copy of 'Tune To Win'. |
| Without getting into pages and pages on the subject, I'll cut to the chase on the matter. The first statement is basically false, because more roll doesn't transfer more load, and even if it did, the resultant changes in dynamic camber would wreak havoc on the tire's contact patches so there would not be more cornering force. The second statement is essentially false in the sense that a car that is strongly restricted from rolling does transfer more weight. |
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| The diagrams above were pretty much taken from |
| Herb Adams - 'Chassis Engineering' - pg.15 |
| This is the best illustration I've found yet that explains how ARBs work, and how they affect both body roll as well as lateral loading. |
| The first diagram shows the frame of the car in a static state, and as such, the wheel pair is equally loaded. |
| The second illustration shows how the anti-roll bar twists in response to the vehicle's frame as it rolls to the left. |
| The third illustration shows how the forces are created at the four points where the bar is attached to the vehicle. |
| Forces 'A' on the suspension increase weight transfer to the outside (left) tire. Forces 'B' on the frame resist body roll. The effect is a reduction of body roll and an increase in load on the laden wheel. |
| The reason why reduced body roll increases lateral loading via the anti-roll bar, rather than the shocks/springs is because the bar directly connects the lower control arms on both sides (the unsprung mass). So the forces are fed directly to the wheels without any damping. |
| The same can't be said for the suspension springs: |
| "The greater the resistance of the springs, the less roll will result - but there will be no significant effect on the amount of lateral load transfer because......there is no physical connection between the springs on opposite sides of the car." |
| -Carrol Smith 'Tune To Win' - pg.38 |
| The heavier the stiffness of the ARB, the more roll resistance we get, and we also get increased lateral weight transfer directly on the outside wheel. |
| Roll stiffness from the ARB is critical because it allows us to control camber change without having to resort to running a very stiff suspension, which will negatively affect tire compliance. |