Delta-Cross
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After completing body design, you are now set to adjust some more parameters of the vehicle that affect its dynamics. The parameters to set here are the load capacity for front and rear axles, anti-roll stiffness for front and rear, and braking force of front and rear. You can also add a wing at the rear to modify the aerodynamic characteristics of the vehicle. On the left, there is a list of values you need to monitor while setting the parameters. Breif discription of these values aregiven below.
Total mass: Total mass of the vehicle.
Sprung mass: Sprung mass of the vehicle.
Unsprung mass (front): Unsprung mass of the front axle.
Unsprung mass (rear): Unsprung mass of the rear axle.
COG height: Height of the center of gravity from the ground level.
COG longl. pos. ratio: Ratio of longitudinal distance of COG from the rear axle to the wheelbase.
Frontal area Af: Frontal area of the vehicle. It will have a value after body design.
Drag coefficient: Value of the coefficient Cd in the aerodynamic drag equation Fd=½ρv2CdAf. It will have a value if you have a designed body.
Lift coefficient (front): Value of the coefficient Cl in the aerodynamic lift equation Fl=½ρv2ClAf at the front axle. Positive value means that the lift is downwards. It will have a value if you have a designed body.
Lift coefficient (rear): Value of the coefficient Cl in the aerodynamic lift equation Fl=½ρv2ClAf at the rear axle. Positive value means that the lift is downwards. It will have a value if you have a designed body.
CoP longl. pos. ratio: Ratio of longitudinal distance of CoP from the rear axle to the wheelbase.
Wheel rate: It is the maximum load capacity of axle divided by maximum suspension travel at an axle.
Ride frequency: Ride frequency at an axle.
Roll moment arm: Distance between CoG and roll axis.
Maximum geometric roll: Maximum roll suspension can allow.
Roll gradient: Amount of roll per 'G' of lateral G-force.
Anti-dive: Anti-dive property of front suspension governed by front suspension geometry. 100% anti-dive means that the vehicle wouldn't dive during braking but 100% anti-dive is never advised. A value around 50%~70% is advisable.
Anti-squat: Anti-squat property of rear suspension governed by rear suspension geometry. 100% anti-squat means that the vehicle wouldn't dive during acceleration but 100% anti-squat is never advised. A value around 50%~70% is advisable.
Anti-lift (front): Anti-lift property of front suspension governed by front suspension geometry. 100% anti-lift means that the vehicle front wouldn't lift during acceleration but 100% anti-lift is never advised. A value around 50%~70% is advisable.
Anti-lift (rear): Anti-lift property of rear suspension governed by rear suspension geometry. 100% anti-lift means that the vehicle rear wouldn't lift during braking but 100% anti-lift is never advised. A value around 50%~70% is advisable.
There is a diagram of the vehicle showing CoG, CoP and forces acting on the vehicle. This diagram also shows sprung and unsprung masses for both front and rear axle. Below it there are some slider bars that allow you to select speed, acceleration and lateral acceleration. Checking the checkbox '-ive' above the acceleration slider gives negative acceleration. This diagram will give you a visualization of how the vehicle would behave under different speed and acceleration scenarios.
At zero speed and acceleration, the only force acting on the vehicle is the weight of the vehicle. You can see downward forces acting on front and rear axle according to weight distribution. If you increase the speed on slider, you will see two forces acting on the CoP of the vehicle that will increase with speed. The horizontal force is the drag force and the vertical force is lift or downforce. If you increase the accelerationon the slider, you will see the inertial force acting on the CoG of the vehicle in a direction opposite to the acceleration. You will observe that this inertial force will affect the downward forces acting on front and rear axle. This is weight shifting effect. If any of these downward forces turn red, it means that the load on that axle has exceeded its load capacity.
During positive acceleration, you will see a horizontal force acting on the tire contact patch of the driven axle. This is the required traction for the given speed and acceleration. If the wheel turns red, it means that the given wheel is unable to provide the required traction.
During negative acceleration, you will see horizontal forces acting on the contact patches of both axles. These are the required traction forces for given speed and acceleration. Values of these forces are proportional to the braking forces for front and rear set in the parameters. If any of these forces turn red in the diagram, it means that the required traction force exceeds the maximum braking force at that axle. If any of the wheel turn red, it means that the given wheel is unable to provide the required traction.
By increasing the lateral acceleration on the slider, you can tell whether the vehicle will understeer or oversteer by checking which wheel turns red first. If front wheel turns red first, the vehicle will understeer. If rear wheel turns red first, the vehicle will oversteer. Please note that this diagram doesn't take into account the suspension parameters such as coils and anti-roll barr stiffness and roll centers etc.
Load capacity parameter of front or rear axle is the maximum amount of load apart from load of the vehicle itself, before the suspension bottoms out for the given axle. It directly affects the wheel rate so increasing the load capacity makes the suspension stiffer. It also affects the ride frequency. You may adjust the load capacity value to get your desired ride frequency. Some guidelines for the ride frequency values are given below.
Anti-roll stiffness parameter is the anti-roll stiffness added to the suspension in addition to the stiffness of the suspension itself through anti-roll bars. This parameter doesn't affect the ride frequency but it affects the roll gradient. So you can get your desired value of roll-gradient without stiffening the suspension. Care should be taken while setting values for front and rear anti-roll stiffness. If front has more anti-roll stiffness, the vehicle would tend to understeer during corners. If rear has more anti-roll stiffness, the vehicle would tend to oversteer during corners. Some guidelines for the ride frequency values are given below.
Brake force parameter is the maximum amount of brake force that is applied to front and rear. Distribution among front and rear should be done carefully. Front and rear brake forces can be set using the vehicle diagram in this tab. While increasing negative acceleration using slider, if the horizontal force at the contact point of tire turns red before the tire, it means that braking force is not enough and more force can be applied to that wheel. Front tires must lockup before rear tires during braking for beter stability and control. So you have to make sure that front tires turn red before rear tires but not by too much.
CoP of the vehicle shouldn't be beyond the CoG otherwise the vehicle would oversteer at high speeds. If it is so, you can move the CoP backwards by adding a rear wing. It can be done by checking the 'Rear wing' checkbox on this tab. Set the parameters for the rear wing that you see upon adding the rear wing. Please not that you have to add a mesh for rear wing in the 'Body design' tab.