SsangYong Actyon Sports II. Manual — part 170

14-16

When the vehicle is driven on a road surface covered with water at high speed, tires do not contact with

the road surface but rotate floating on a thin film of water.

It causes brake failure, lower traction force and losing the steering performance.

To prevent this, increase the tire inflation pressure, use tires with leaf shape tread which is not worn.

However, it is a best measure to drive slowly.

Hydro Planing

▶

Vehicle speed ≤ 60 km/h

No Hydro planning

Vehicle speed = 80 km/h

Partial Hydro planning

Vehicle speed ≥ 100 km/h

Full Hydro planing

14-17

4170-09

If weight is not equally distributed around the wheel, unbalance centrifugal force by the wheel rotation

produces vibration. As the centrifugal force is produced proportional to the square of the rotating speed,

the wheel weight should be balanced even at high speed. There are two types of the tire and wheel

balancing: static and dynamic. Abnormal vibration may also occur due to unbalanced rigidity or size of

tires.

Static Balance

▶

When the free rotation of the wheel is allowed,

the heavier part is stopped on the bottom if the

wheel weight is unbalanced and this is called

"Static Unbalance". Also, the state at which tire's

stop position is not same is called "Static

Balance" when the wheel is rotated again. If the

part A is heavier as shown in the figure 1, add

the balance weight of a weight corresponding to

unbalanced weight from B to A to maintain the

static balance. If the static balance is not

maintained, tramping, up and down vibration of

the wheels, occurs.

Dynamic Balance

▶

The static unbalance of the wheel creates the

vibration in the vertical direction, but the dynamic

unbalance creates the vibration in the lateral

direction. As shown in the figure 2 (a), if two

parts, (2) and (3), are heavier when the wheels

are under the static balance condition, dynamic

unbalance is created, resulting in shimmy, left

and right vibration of the wheels, and the torque

Fxa is applied in the axial direction. To correct

the dynamic unbalance, add the balance weight

of a same weight for two points of the

circumference of the rim, A and B, as shown in

the figure 2 (b), and apply the torque in the

opposite direction to the torque Fxa to offset in

order to ensure smooth rotation of the wheel.

Center

A

B

(a) (b)

[Figure 1]

[Figure 2]

3. WHEEL BALANCE

14-18

4. WHEEL ALIGNMENT

▶Toe-in

▶Camber

In automotive engineering, toe, also known as

tracking, is the symmetric angle that each wheel

makes with the longitudinal axis of the vehicle, as a

function of static geometry, and kinematic and

compliant effects. This can be contrasted with

steer, which is the anti-symmetric angle, i.e. both

wheels point to the left or right, in parallel (roughly).

Positive toe, or toe in, is the front of the wheel

pointing in towards the center line of the vehicle.

Negative toe, or toe out, is the front of the wheel

pointing away from the center line of the vehicle.

Toe can be measured in linear units, at the front of

the tire, or as an angular deflection.

Camber is the angle made by the wheels of a

vehicle; specifically, it is the angle between the

vertical axis of the wheels used for steering and

the vertical axis of the vehicle when viewed from

the front or rear. It is used in the design of steering

and suspension. If the top of the wheel is farther

out than the bottom (that is, away from the axle), it

is called positive camber; if the bottom of the

wheel is farther out than the top, it is called

negative camber.

Wheel alignment consists of adjusting the angles of the wheels so that they are parallel to each other

and perpendicular to the ground, thus maximizing tire life and ensures straight and true tracking along a

straight and level road.

Camber angle alters the handling qualities of a particular suspension design; in particular, negative

camber improves grip when cornering. This is because it places the tire at a better angle to the road,

transmitting the forces through the vertical plane of the tire rather than through a shear force across it.

Another reason for negative camber is that a rubber tire tends to roll on itself while cornering. Negative

camber can also be caused by excessive weight on the front wheels. This is commonly seen on

modified cars with larger engines than standard; the weight of the modified engine can make the wheels

negatively camber. The inside edge of the contact patch would begin to lift off of the ground if the tire had

zero camber, reducing the area of the contact patch. This effect is compensated for by applying negative

camber, maximizing the contact patch area. Note that this is only true for the outside tire during the turn;

the inside tire would benefit most from positive camber.

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4170-09

▶Caster

Caster is the angle to which the steering pivot

axis is tilted forward or rearward from vertical, as

viewed from the side. If the pivot axis is tilted

backward (that is, the top pivot is positioned

farther rearward than the bottom pivot), then the

caster is positive; if it's tilted forward, then the

caster is negative.

Positive caster tends to straighten the wheel

when the vehicle is traveling forward, and thus is

used to enhance straight-line stability. The

mechanism that causes this tendency is clearly

illustrated by the castering front wheels of a

vehicle. The steering axis of a vehicle wheel is

set forward of where the wheel contacts the

ground. As the vehicle is driving forward, the

steering axis pulls the wheel along, and since the

wheel drags along the ground, it falls directly in

line behind the steering axis. The force that

causes the wheel to follow the steering axis is

proportional to the distance between the steering

axis and the wheel-to-ground contact patch-the

greater the distance, the greater the force. This

distance is referred to as "trail."