Page 304 - Automotive Engineering Powertrain Chassis System and Vehicle Body

Tyres and wheels C HAPTER 10.1

Fig. 10.1-28 Tyre springing rate as a function of slip angle and road speed, measured on a radial tyre 185/70 R 13 86 S at p T ¼ 2.1
bar. Speed increases the springing rate as the belt stands up due to the centrifugal force. However, the slip angle makes it softer
because the belt is pushed away to the side and the shoulders take over part of the springing effect.

10.1.5 Non-uniformity differentiate between static and dynamic imbalance
(Fig. 10.1-29). This is calculated in size and direction on
The tyre consists of a number of individual parts, e.g. balancing machines and eliminated with balancing
carcass layers, belt layers, running tread, sidewall stock weights on the rim bead outside and inside the wheel.
and inner lining, which – put together on a tyre rolling Radial and lateral runout are the geometrical variations
machine – give the tyre blank (Fig. 10.1-5). In the area in the running tread and the sidewalls. They are measured
where it is put together, variations in thickness and with distance sensors on a tyre-uniformity machine. The
stiffness occur, which can lead to non-uniformity. German WdK Guideline 109 contains full details.
Owing to the irregularities caused during manufac- The most important of the three force variations is the
ture, the following occur around the circumference and radial force variation. For greater clarity, it is shown on
width of the tyre: the model in Fig. 10.1-30, where the tyre consists of
different springs whose rates fluctuate between c 1 and c 8 .
thickness variations The resulting phenomena should be indicated on the
mass variations
stiffness variations.
These cause various effects when the tyre rolls:
imbalance
radial tyre runout
lateral tyre runout
variation in vertical and/or radial force
lateral force variations
longitudinal force variation
ply steer (angle) force
conicity force. (a) Static (b) Dynamic (c) Moment of
Imbalance U occurs when an uneven distribution of mass imbalance imbalance imbalance
and the resulting centrifugal forces are not equalized.
Because the uneven distribution occurs not only Fig. 10.1-29 Different forms of imbalance U: (a) static,
around the circumference, but also laterally, we have to (b) dynamic. The imbalance is equalized in (c).

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