| ANTI ROLL BARS | ||
| When it comes to tuning, you will find as you experiment with your Forza Motorsport 3 race cars that the Anti-Roll Bar (ARB) is one of your best friends. The dynamic relationship between the ARB and suspension springs can be tricky and is often misunderstood. We'll try to clarify as best we can. | ||
| TERMS TO KNOW | ||
| Body Roll: | Because the vast majority of vehicle weight is part of the sprung mass (suspended on the springs) the vehicle is subjected to a wide variety of movements, one of which is body roll. Simply put, body roll is the effect of the car leaning or tilting toward one side or the other during a turn. The body will always lean toward the outside of the turn due to centrifugal force. | |
| Roll Angle: | This is the measurement of body roll in degrees. Increased roll angles adversely affect the way the car handles because it changes the camber angle of the tires relative to the road surface. | |
| Roll Stiffness: | Is the measurement of the resistance of the vehicle's sprung mass to body roll. | |
| THE EFFECTS OF BODY ROLL | ||
| Simply put, body roll is bad. And it can be inferred from the name 'ARB' that the job of the Anti Roll Bar is to reduce this negative effect. To further understand why body roll is bad, read the sections on camber. | ||
| When the car rolls, the action of the suspension going into the bump and rebound phases of its movement causes 'dynamic camber change'. This change in camber angle as the body rolls up on the outside tires in a corner is bad for the overall tractive capacity of the tire. Since we want to keep the tires as upright as possible and maximize the contact patch, the act of the car rolling the tire to the outer edge is something we really don't want. We can offset these camber changes with our static negative camber settings, but we can only angle the tires so far since too much negative camber leads to a whole host of other issues that are undesirable. | ||
| The other negative effect of body roll is it makes the car sloppy and unresponsive, especially in transitions from left to right, and vice versa. Too much body roll slows down the process of the race car taking its set, especially on corner exit when we want to put the power down. | ||
| The anti roll bars are the most effective way to limit body roll in our attempt to offset the aforementioned negative effects of body roll. | ||
| The roll resistance of the ARBs are affected by two main factors: | ||
| 1- Bar diameter 2- Swing arm length |
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| The diagram to the right is a simple illustration of an anti-roll bar. The thicker the bar, the more roll resistance it will provide. The swing arm is the vertical component of the ARB. The shorter the swing arm length, the greater the roll resistance it provides and vice versa. The greater the resistance to body roll, the more weight is transferred from one side of the car to the other (lateral load transfer). In the practical sense, the increase in lateral weight transfer bypasses the suspension and goes directly from the left side tires to the right side tires and vice versa. | ||
| For additional information on the relationship between ARBs and body roll, read the section: Basics - Dynamics 2 |
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| A QUESTION FOR THE AGES | ||
| Based on the information provided, you might be inclined to ask, "If body roll is bad, and ARBs resist body roll, why not just run your bars stiff enough to eliminate it altogether?" | ||
| It's a good question that has a simple answer. Because ARBs transfer weight directly from the inside tires to the outside tires, too much ARB stiffness will eventually overload the laden wheels when cornering. If you haven't read the sections on Tires, you'll probably want to. It's important to remember that a pair of tires has its maximum grip ability when both tires are equally loaded. Check out the TIRE PERFORMANCE CURVE. When you increase load on the outside tire you decrease load on the inside tire. Although an increased load on the outside tire increases that tire's grip, the overall grip of the tires as a pair decreases. | ||
| his information might lead you to nod your head then ask another question: "If the overall grip of a pair of tires is greatest when both are equally loaded, why not eliminate the ARBs to reduce lateral load transfer as much as possible in the corners, and use the springs to reduce body roll?" | ||
| Another good question that has another simple answer. If you read the section on Springs, you'd recall that the springs primary function is tire compliance with the road surface. If you were to set up your car without ARBs and rely on the springs only to reduce body roll to an acceptable level, the ride would be so stiff that there wouldn't be enough suspension travel to keep the tires in contact with the road. | ||
| THE ANTI ROLL BAR - THE TUNER'S BEST FRIEND | ||
| So, we're discovering that the ARB is an effective tool that, when working in harmony with the springs, reduces body roll and controls the amount of lateral weight transfer between wheel pairs. But as far as its usefulness to the tuner, the ARB is hands down the number one tool for balancing the oversteer/understeer characteristics of the race car. | ||
| I'd like to take this opportunity to give props to the effectiveness of aero, in this capacity, as well. The reason I say that the ARB gets top billing is because of the versatility of the sway bar in all driving situations that arise on the track. Aero is only effective at higher speeds, above 60 mph or thereabout, but does little to balance the car in the slow corners, hairpins, and sweepers. | ||
| The other advantage of mastering the usage of the ARB is their relative ease and simplicity of adjustment. We can use the springs/shock combination to adjust oversteer/understeer, but shock absorber adjustment is a 'black art' that can be dicey and complicated. Add in the adjustment of springs for balance, and now we have to be concerned with mucking up our tire compliance and the relative effect in dynamic camber change that will result. | ||
| Experimenting with the ARB is arguably the most harmless of the adjustments we can make to balance the race car. Also note that if you're inclined to go the route of buying a tuned car from a tuning garage, but like a car that's a little looser or little tighter, playing around with the sway bars is a fun and easy way to tweak the car to suit your driving style. | ||