steering theory

Questions:

1.Why is negative caster undesirable?

2.Why is too much positive caster undesirable?

3.What are the effects of a high kinpin lateral offset

4.For reverse Ackermann, does the outer wheel steer more or less than the inner wheel?

5.If the turn center for the front wheels is at a distance of 4000 mm behind the front axle and the wheelbase is 2700 mm, what is the �kermann?

6.How does the Revoknuckle geometry help reduce torque steer?

7.What are the two types of tierod errors with respect to ride steer? And what is the effect of these errors on the toe curve?

Answers:

1. Negative caster aids the steering and largely reduces steering effort but this makes the vehicle unstable.
2. It not only increases the steering effort but, also increases the mechanical trail. High mechanical trail results in the low loss of steering feedback which does not help the driver in recognizing the loss of grip.
3. When there is a torque imbalance between the left and right wheels (in front wheel drives), torque steer occurs. Kingpin offset acts as a moment arm. Hence, high kingpin lateral offset would further amplify the torque steering effect.
4. for reverse acherman:The outer wheel steers more than the inner wheel
5. Given: distance of turn center from front axle, x=4000mm

Wheel base=2700mm

%Ackermann = (wheel base/x)

%Ackermann = 2700/4000 = 0.675

%Ackermann = 67.5%

6. Revoknuckle design favours in significantly reducing the spindle length, the perpendicular distance between the wheel centre and the kingpin axis, which acts as the moment arm for torque steer. This way the torque steer reduced
7. The two errors are:

a)Tie rod length error- If the tie rod ends are not on the locus of line joining the points upper control arm pivot & lower control arm pivot OR upper ball joint & lower ball joint

Effect : Parabolic toe (out) curve in jounce & rebound( undesirable with no steering net effect, and it can lead to changing from understeer to oversteer when ride height changes)

Tie rod angle error- The tie rod is not aiming at instantaneous center.

Effect on toe curve - linear but sloped curve maybe used to add roll understeer in suspension