4.1.13. Noise of swing of tires
General information on swing noise
The swing noise perceived by a human ear are the fluctuations proceeding from a source of a sound and by air reaching an ear.
Here the noise arising due to certain features and also effects when swing tires (a noise source) are interesting.
The cause of noise in the most part depends on a combination of tires and a paving.
The structure of a surface and material of a roadbed also strongly influence swing noise. Noise level on the wet road, for example, is much higher, than on dry.
Profiling of the drawing of a protector strongly influences noise level. Tires with cross flutes at an angle 90 ° more noisy, than tires with diagonal flutes.
Small blocks of a protector are unstable. Because of their strong deformation when swing tires the air is rended. Air fluctuations are created. which lead to noise.
Wider tires shumny. For water drainage they have to have more flutes. When swing because of these flutes air is forced out at the expense of what there are also air fluctuations.
The other effects influencing noisiness.
"Fluctuation of the tire" is the main reason for noise of swing. They arise because of excitement of air columns in protector flutes.
"The air pulsation" is a compression and expansion of air at arrival of the area of contact of the tire on a roadbed at which it is deformed protector blocks.
Noisiness of tires
Noisiness generally is defined by tires and a paving.
The qualities of a paving influencing noisiness is a roughness (roughness), structure and material.
Parameters of influence of the tire, except other, are width of the tire and a disk. Wider tire because of the bigger area of contact with a paving creates more noise as the bigger volume of air is squeezed out and big "weight" is excited in fluctuations, than at the smaller size.
Wider the disk also increases the area of contact of the tire. Thus, influence on noisiness same, as well as at the wide tire. Besides wider disks negatively affect the damping properties of the tire.
Noise of swing of tires are heard in cars at which the engine is installed in a forward part, it is better on back seats as aerodynamic noise and a sound of the engine in this place of salon stir less.
Wear of a protector in the form of a path of a sawtooth form
Wear of a protector in the form of a path of a sawtooth form is a step wear of separate blocks of a protector that can result in the increased noisiness. Wear of a sawtooth form happens because of uneven deformation of blocks of a protector on the surface of contact of the tire with a paving. Such type of wear is more often shown on not driving wheels, than on leaders.
New tires are more inclined to wear of a protector of a sawtooth form as high blocks of a protector are more elastic. With reduction of depth of the drawing of a protector rigidity of blocks of a protector increases, tendency to such type of wear decreases.
A – Blocks of a protector of the new tire; protector blocks if to look in the direction of swing an arrow 1, are identical on height in front and behind.
B – Wear of a protector in the form of a path of a sawtooth form; protector blocks if to look in the direction of swing an arrow 1, in front above, than behind an arrow 2.
C – Profile blocks, a look in the direction of swing an arrow 1, have strong wear in a forward part of "tooth" an arrow 3.
At strongly expressed wear of a protector in the form of a path of a sawtooth form there can be noticeable an amplified noisiness of tires.
Strong wear of a protector in the form of a path of a sawtooth form happens at too big convergence the wrong pressure of air in tires to big blocks of a protector the tires installed on wheels not of a driving axis extreme passing of bends.
Tires with not directed drawing of a protector
At detection of wear of a protector in the form of a path of a sawtooth form it is necessary to change the direction of swing of the tire. If the increased wear of a protector in the form of a path of a sawtooth form and the increased noisiness is found, it is necessary to rearrange wheels cross-wise. It will reduce wear.
On cars with the forward drive efficiency of this approach will be even more noticeable thanks to bigger attrition of tires on a forward axis.
Swing noise directly after shift of wheels will be slightly stronger, however after the run of 500-1000 km the normal level of noisiness will be reached again.
Tires with the directed drawing of a protector
At the increased wear of a protector in the form of a path of a sawtooth form on tires of a back axis – mainly at the forward drive – it is necessary to rearrange back wheels forward. At the increased sawtooth wear on external edges on one axis both tires should be turned on a disk. After that the left wheel should be mounted on the right side, and the right wheel on left.
Wear spots because of the movement with the blocked wheels
Fig. 4.12. Wear spots on a protector because of braking with the blocked wheels
This type of wear is a consequence of strong braking with the blocked wheels at which on the area of contact of the tire with a paving rubber of a protector (fig. 4.12)
When sliding tires on a roadbed heat of friction which reduces resistance to protector material attrition is developed.
Even the most wearproof rubber mixes of protectors do not exclude wear spots which can be formed at extreme braking.
And even the brake systems equipped with ABS do not exclude short-term blocking and by that small wear.
Extent of such attrition significantly depends on the speed of the movement, a paving and load of a wheel. The following examples are for descriptive reasons given.
When braking the car with the blocked forward wheels on a dry paving to a full stop wear of rubber on the area of contact, an equal post card, will make:
– from 57 km/h = 23,8 m of a brake way to 2,0 mm;
– from 75 km/h = 41,8 m of a brake way to 3,3 mm;
– from 92 km/h = 71,6 m of a brake way to 4,8 mm.
Tires with similar damages are unsuitable for further operation and have to be replaced.
Reasons of not smoothness of the course
Reasons of not smoothness of the course various. Not smoothness of the course can appear including from behind wear of tires. In use tires not always wear out evenly on all surface of a protector. The small imbalance which prevents quiet swing of earlier ideally balanced wheel already appears from behind it.
Such imbalance is not felt on a wheel yet, however takes place. It increases wear of the tire and reduces thereby service life.
That throughout all service life of the tire to ensure optimum safety, the optimum smooth course and uniform wear, disks with tires not less than two times during service life of tires are recommended to balance.