Bundorf analysis
Encyclopedia
A Bundorf analysis is a way of describing the characteristics of a vehicle that govern its understeer
balance. The understeer is measured in units of degrees of additional yaw per g of lateral acceleration.
Hence the total understeer is 11.0-6.9 deg/g, or 4.1 deg/g.
Negative values are oversteering, positive values are understeering, for that axle. If the understeer contribution of the rear axle is greater than that of the front axle you get negative understeer, which is known as oversteer. The analysis is only applicable while the parameters remain constant, and thus only up to about 0.4 g.
changes. The latter is known as the cornering stiffness of the tire. See also Tire load sensitivity
Aligning torque. The tire does not just generate a lateral force, it generates a torque as well. This tends to rotate the vehicle as a whole.
Roll camber. As the vehicle rolls the kinematics of the suspension provide a change in the camber of the tire. This generates a force known as camber thrust.
Roll steer. As the vehicle rolls the kinematics of the suspension provide a change in the steer angle of the tire. This generates a cornering force in the normal way.
Fy compliance steer. The lateral force at the contact patch
causes the wheel to rotate about the steer axis, generating a steer angle.
SAT compliance steer. The aligning torque directly twists the wheel on the compliances in the suspension, generating a steer angle.
Understeer. In this case, the tendency for an axle or vehicle to turn outwards from a corner.
Understeer
Understeer and oversteer are vehicle dynamics terms used to describe the sensitivity of a vehicle to steering. Simply put, oversteer is what occurs when a car turns by more than the amount commanded by the driver...
balance. The understeer is measured in units of degrees of additional yaw per g of lateral acceleration.
An imaginary example
| Front | Rear | |
|---|---|---|
| deg/g | deg/g | |
| Load transfer effect and cornering stiffness of tire | 8.0 | 7.0 |
| Aligning torque | 0.2 | -0.2 |
| Roll camber | 1.2 | 0.0 |
| Roll steer | 0.6 | -0.4 |
| Fy Compliance steer | 0.3 | -0.1 |
| SAT compliance steer | 0.7 | 0.6 |
| Total Axle Cornering compliance | 11.0 | 6.9 |
Hence the total understeer is 11.0-6.9 deg/g, or 4.1 deg/g.
Negative values are oversteering, positive values are understeering, for that axle. If the understeer contribution of the rear axle is greater than that of the front axle you get negative understeer, which is known as oversteer. The analysis is only applicable while the parameters remain constant, and thus only up to about 0.4 g.
Explanation of terms
Load transfer effect and cornering stiffness of tire. As load transfers across the vehicle the tire's ability to provide cornering force for a given slip angleSlip angle
In vehicle dynamics, slip angle or sideslip angle is the angle between a rolling wheel's actual direction of travel and the direction towards which it is pointing...
changes. The latter is known as the cornering stiffness of the tire. See also Tire load sensitivity
Tire load sensitivity
Tire load sensitivity describes the behaviour of tires under load. Conventional pneumatic tires do not behave as classical friction theory would suggest...
Aligning torque. The tire does not just generate a lateral force, it generates a torque as well. This tends to rotate the vehicle as a whole.
Roll camber. As the vehicle rolls the kinematics of the suspension provide a change in the camber of the tire. This generates a force known as camber thrust.
Roll steer. As the vehicle rolls the kinematics of the suspension provide a change in the steer angle of the tire. This generates a cornering force in the normal way.
Fy compliance steer. The lateral force at the contact patch
Contact patch
Contact patch is the portion of a vehicle's tire that is in actual contact with the road surface. It is most commonly used in the discussion of pneumatic tires, , where the term is strictly used to describe the portion of the tire’s tread that touches the road surface...
causes the wheel to rotate about the steer axis, generating a steer angle.
SAT compliance steer. The aligning torque directly twists the wheel on the compliances in the suspension, generating a steer angle.
Understeer. In this case, the tendency for an axle or vehicle to turn outwards from a corner.