A Bundorf analysis is a measure of the characteristics of a vehicle that govern its

understeer Understeer and oversteer are vehicle dynamics terms used to describe the sensitivity of the vehicle to changes in steering angle associated with changes in lateral acceleration. This sensitivity is defined for a level road for a given steady state ...

balance. The understeer is measured in units of degrees of additional yaw per g of lateral acceleration.

An imaginary example

Hence the total under-steer is 11.0 deg/g minus 6.9 deg/g, or 4.1 deg/g. Negative values are over-steering, positive values are under-steering, for that axle. If the under-steer contribution of the rear axle is greater than that of the front axle you get negative under-steer, which is known as

oversteer Understeer and oversteer are vehicle dynamics terms used to describe the sensitivity of the vehicle to changes in steering angle associated with changes in lateral acceleration. This sensitivity is defined for a level road for a given steady state ...

. 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 angle In vehicle dynamics, slip angle or sideslip angle is the angle between the direction in which a wheel is pointing and the direction in which it is actually traveling (i.e., the angle between the forward velocity vector v_x and the vector su ...

changes. The latter is known as the cornering stiffness of the tire. See also

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. The load sensitivity of most real tires in their typical operating range is such that the c ...

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 Camber thrust and camber force are terms used to describe the force generated perpendicular to the direction of travel of a rolling tire due to its camber angle and finite contact patch. Camber thrust is generated when a point on the outer surface ...

Roll steer Bump steer is the term for the tendency of the wheel of a car to steer itself as it moves through the suspension stroke. Bump steer causes a vehicle to turn itself when one wheel hits a bump or falls down into a hole or rut. Excessive bump 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 The contact patch is the portion of a vehicle's tire that is in actual contact with the road surface. It is commonly used in the discussion of pneumatic (i.e. pressurized) tires, where the term is used strictly to describe the portion of the tire' ...

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. Under-steer. In this case, the tendency for an axle or vehicle to turn outwards from a corner.

References

Bundorf, R.T. and Leffert, R.L. (1976) 'Cornering compliance concept for description of vehicle. directional control properties', SAE paper 760713 {{AutomotiveHandlingNav Automotive safety Automotive steering technologies Automotive suspension technologies