Forces Wheel and Road

Question 1

μy is, in absence of spoilers and high adherence tires:

a. 0.2 – 0.4;
b. 0.5 – 0.7;
c. 0.7 – 1.0.

Answer 1

b. 0.5 – 0.7;

Question 2

At high sideslip angles, the self-alignment torque is:
a. Still increasing with the sideslip angle, but less than for small sideslip angles;
b. Decreasing with increasing the sideslip angle, but can never invert its sign;
c. Decreasing with increasing the sideslip angle and after a certain point it changes sign.

Answer 2

c. Decreasing with increasing the sideslip angle and after a certain point it changes sign.

Question 3

3) Which effect has the wear for a conventional tire?
a. Decreases the rolling coefficient and increases its critical speed;
b. Increases the rolling coefficient and decreases the critical speed;
c. Increase both the rolling coefficient and the critical speed of the tire.

Answer 3

a. Decreases the rolling coefficient and increases its critical speed;

Question 4

4) Of what does it depend the total adherence coefficient μ=T/Z ?
a. Depends only on the direction of, T;
b. Has a high dependence on the normal load, Z;
c. It depends on the direction of the resultant force, T, and a little bit of the normal load, Z.

Answer 4

c. It depends on the direction of the resultant force, T, and a little bit of the normal load, Z.

Question 5

5) The direction of the drift forces:
a. Along x;
b. Along y;
c. Along the direction of v.

Answer 5

b. Along y;

Question 6

6) The resonance frequencies of a conventional and a radial tire:
a. 120 Hz (radial), 80 - 100 Hz (conventional);
b. 80 -100 Hz (radial), 120 Hz (conventional);
c. 60 - 80 Hz (radial), 140 Hz (conventional)

Answer 6

b. 80 -100 Hz (radial), 120 Hz (conventional);

Question 7

7) The rolling coefficient employs adherence
a. Only for the driving wheels;
b. Only for the driven wheels;
c. For both.

Answer 7

b. Only for the driven wheels;

Question 8

The concept of drift angle is valid:
a. Always;
b. Only for rotations around an equilibrium point (symmetry);
c. Only for small rotations around a single point.

Answer 8

b. Only for rotations around an equilibrium point (symmetry);

Question 9

9) The Gough diagram represents:
a. Na as a function of α;
b. α as a function of Na;
c. Na parameterized with α and Z (Na would be Fy and Z would be Fz ).

Answer 9

c. Na parameterized with α and Z (Na would be Fy and Z would be Fz ).

Question 10

10) The Pacejka model serves to express:
a. The longitudinal and lateral forces, and the self-alignment torque as function of the normal
load, of the longitudinal slip, of the sideslip angles and of the wheel camber;
b. The longitudinal and lateral forces as functions of the normal load, of the drift and of the
temperature;
c. The longitudinal and lateral forces and the self-alignment torque as functions of the normal
load, of the drift and of the sideslip angle, but it don’t take into account the camber angle.

Answer 10

a. The longitudinal and lateral forces, and the self-alignment torque as function of the normal
load, of the longitudinal slip, of the sideslip angles and of the wheel camber;

Question 11

11) The rolling radius increases with increasing the vehicle speed:
a. False;
b. True, for radial tires;
c. True, for conventional tires.

Answer 11

c. True, for conventional tires.

Question 12

12) The rolling radius of a tire in pure rolling is:
a. Equal to its unloaded radius;
b. Equal to the radius under load;
c. Intermediate.

Answer 12

c. Intermediate.

Question 13

13) The rolling radius of a braking wheel is:
a. Lower than the radius under load;
b. Greater than the unloaded radius;
c. Intermediate.

Answer 13

b. Greater than the unloaded radius;

Question 14

14) The rolling radius of a driving wheel is:
a. Smaller than the loaded radius;
b. Greater than the unloaded radius;
c. Intermediate.

Answer 14

a. Smaller than the loaded radius;

Question 15

15) The adherence in slipping conditions is much lower than the maximum achievable adherence:
a. False;
b. Always true;
c. Always true, but specially at high speed and wet road.

Answer 15

c. Always true, but specially at high speed and wet road.

Question 16

16) The longitudinal grip of a tire as a function of the slip:
a. Is always increasing;
b. At first increases;
c. At first increases and then decreases.

Answer 16

c. At first increases and then decreases.

Question 17

17) The longitudinal adherence in slipping conditions is much lower than the one in motion conditions:
a. False;
b. Always true;
c. Always true, but specially at high speed and wet road.

Answer 17

c. Always true, but specially at high speed and wet road.

Question 18

18) The lateral grip coefficient, µy:
a. Doesn’t depend on the vertical load, Z;
b. Increases with increasing the load, Z;
c. Decreases with increasing the load Z.

Answer 18

c. Decreases with increasing the load Z.

Question 19

19) The transversal adherence of a tire as a function of the sideslip angle:
a. Is always increasing;
b. Is increasing and then constant;
c. Decreases with increasing the vertical load,
Z.

Answer 19

b. Is increasing and then constant;

Question 20

20) The sideslip force is applied:
a. Behind the contact patch’s center;
b. In front of the contact patch’s center;
c. At the contact patch’s center.

Answer 20

a. Behind the contact patch’s center;

Question 21

21) The resonance frequency of the first vibrational mode of a radial tire, with respect to the one of a
conventional tire, is:
a. Greater;
b. Approximately equal;
c. Lesser

Answer 21

c. Lesser.

Question 22

22) The rolling resistance test of a tire:
a. Doesn’t allow to get much reliable results because it can’t purge the inertia of the tire-road;
b. Doesn’t allow to get much reliable results because there is no thermal equilibrium;
c. Doesn’t allow getting much reliable results because it doesn’t consider the resistance of the
bearings of the wheels.

Answer 22

b. Doesn’t allow to get much reliable results because there is no thermal equilibrium;

Question 23

23) The rolling resistance of the driving wheels doesn’t employs adherence:
a. So, it is not counted on the energetic balance;
b. At the power needed for motion it is necessary to consider the rolling resistance of the driven
wheels;
c. The rolling resistance of the driving wheels is directly overcome by the applied driving torque.

Answer 23

c. The rolling resistance of the driving wheels is directly overcome by the applied driving torque.

Question 24

24) The rolling resistance, as the load increases (constant pressure):
a. Increases;
b. Reduces;
c. Remains substantially constant.

Answer 24

a. Increases;

Question 25

25) The rolling resistance as the temperature increases: a. Increases; b. Decreases; c. Remains substantially constant.

Answer 25

b. Decreases;

Question 26

26) The rolling resistance increases if the inflating pressure: a. Increases; b. Decreases; c. Remains constant.

Answer 26

b. Decreases;

Question 27

27) The rolling resistance is due mainly: a. To the hysteresis; b. To the drag of the contact patch; c. To the vibrations.

Answer 27

a. To the hysteresis;

Question 28

28) The rolling resistance is preponderant with respect to the aerodynamic one: a. At high speed; b. At a tilted road; c. At low speed.

Answer 28

c. At low speed.

Question 29

29) The cornering stiffness, for small sideslip angles, is: a. Co√1−( Y Y MAX ) 2 , which would be ( X X MAX ) ; b. Y ; c. µy.

Answer 29

a. Co√1−( Y Y MAX ) 2 , which would be ( X X MAX ) ;

Question 30

30) The cornering stiffness is measured in: a. N/m; b. Nm/rad; c. N/rad.

Answer 30

c. N/rad.

Question 30

30) The cornering stiffness31) The cornering stiffness: a. Grows always with the increase of the normal load, Z; b. First grows and then becomes constant with the load, Z; c. Doesn’t depend on the load. is measured in: a. N/m; b. Nm/rad; c. N/rad.

Answer 30

b. First grows and then becomes constant with the load, Z;

Question 30

32) The critical speed of a tire is due to: a. The unsaturation of the vibrations at the coverage; b. The tire’s overheating; c. The pressure variations.

Answer 30

a. The unsaturation of the vibrations at the coverage;

Question 31

33) The critical speed of a tire is the one at which: a. The tire loses its capacity of generating motor or braking forces; b. The rolling resistance has a rapid growth; c. The tire loses its capacity of generating longitudinal and transversal forces.

Answer 31

b. The rolling resistance has a rapid growth;

Question 32

34) The slipping velocity v of the wheel is: a. Different from zero if the wheel is slipping; b. Always different from zero; c. In general, different from zero if there are longitudinal forces.

Answer 32

c. In general, different from zero if there are longitudinal forces.

Question 32

35) The grooves improve the adherence: a. Always; b. Only on wet road; c. Never, their presence is only useful in the presence of dynamic effects of the tire.34) The slipping velocity v of the wheel is: a. Different from zero if the wheel is slipping; b. Always different from zero; c. In general, different from zero if there are longitudinal forces.

Answer 32

b. Only on wet road;.

Question 33

36) At the Gough diagram there are represented: a. The drifting force as function of the sideslip angle (parameterizing the load); b. The self-alignment torque as function of the sideslip angle (parameterizing the load); c. The drifting force as function of the self-alignment torque (parameterizing the load and α).

Answer 33

c. The drifting force as function of the self-alignment torque (parameterizing the load and α).c. In general, different from zero if there are longitudinal forces.

Question 34

37) At the force-deformation test for tires, executed over concave and convex surfaces, which differences there are between the two? a. The registered values over the concave are about 20% greater with respect to the one over convex surfaces; b. The registered values over the convex are about 20% greater with respect to the one over concave surfaces; c. There are no differences between the two tests.

Answer 34

a. The registered values over the concave are about 20% greater with respect to the one over convex surfaces;

Question 34

38) The order of magnitude of the rolling coefficient: a. 0.013; b. 0.001; c. 0.0001.

Answer 34

a. 0.013;

Question 34

39) The order of magnitude of f at low speed, at good condition tarmac track: a. 0.0001; b. 0.001; c. 0.01.

Answer 34

c. 0.01.

Question 35

40) For small sideslip angles, the cornering stiffness C of the tires depends on: a. The longitudinal slip, σ; b. The sideslip angle, α; c. Both.

Answer 35

c. Both.

Question 36

41) For small sideslip angles, in a first approximation, the cornering stiffness is: a. C=Co√ 1−( X Z.μxMAX ) 2 ; b. C=Co√1−( Y Z.μxMAX ) 2 ; c. C=Co√ 1−( X Z.μx ) 2 .

Answer 36

a. C=Co√ 1−( X Z.μxMAX ) 2 ;

Question 37

42) When is the slipping velocity of the tire equal to zero? a. In general, when there are no longitudinal forces; b. When there are no forces applied on the tire; c. When the tire is rolling over a very slippery surface (rotation without translation).

Answer 37

a. In general, when there are no longitudinal forces;

Question 38

43) If α is different from zero, where is it measured the rolling resistance? a. Along x direction; b. Along y direction; c. Along the direction of the velocity.

Answer 38

c. Along the direction of the velocity.

Question 39

44) If the wheel doesn’t exert any longitudinal forces: a. Theτ x are not null, but their resultant is null; b. The τ x are not null, and their resultant is not null; c. The τ x are null.

Answer 39

a. Theτ x are not null, but their resultant is null;

Question 40

45) A tire works in rapidly changing load conditions over time. The drifting force that it is able to generate is: a. Lower than the one exercisable at constant load; b. Equal to the one exercisable at constant load; c. Greater than the one exercisable at constant load.

Answer 40

a. Lower than the one exercisable at constant load;

Question 41

46) A tire is exerting longitudinal forces X and transversal Y. the total adherence: a. Is independent of the resultant; b. Depends on the direction of the resultant; c. Doesn’t depend on the load Z.

Answer 41

b. Depends on the direction of the resultant;