Wheels and tires. Device, purpose and marking

6.2.1 Purpose of wheels

Note
In this chapter, we will call all the elements not as is customary in colloquial speech, but in a scientific way, so that an understanding of the essence of things is formed.

The wheel and the tire together form a wheel propeller, which is designed to connect the car with the road, ensure its movement, change the direction of movement and transfer vertical loads from the car to the road and vice versa. Simply put, it is thanks to this propeller that we can move and control the car. Therefore, the behavior of the car on the road directly depends on the correct choice of wheels and tires.

6.2.2 Wheel types

The following types of propellers are distinguished:

• driving;
• driven;
• combined (driving and driven);
• idle (non-driving and uncontrollable, for example, trailer wheels or supported in multi-axle trucks).

Driving propellers got their name precisely because they convert the engine thrust into the forward motion of the car, transferring all the moments and forces to the road. The driven propellers are solely responsible for controlling the direction of movement of the vehicle. And in case if the propeller receives thrust from the engine, and even is responsible for the direction of movement, then it is combined. Idle propellers are used for evenly distributing the weight of the vehicle on the road surface.

Wheel propeller (Figure 6.20) consists of inflated tire, a hub and a wheel (which consists of a disk and a rim).

Figure 6.20 Wheel propeller. Cross-section.

Inflated tire is the most important element in the wheel propeller design. If we imagine a wheel propeller without a pneumatic tire - rigid, for example, a wooden one, then it is easy to assume that when it rolls on a solid road, the trajectory of the axle movement will copy the road profile. In this case, the impacts of the wheel propeller on bumps will be fully transmitted to the suspension. And everything looks very different when the wheel propeller has an inflated tire. At the point of contact, an elastic tire (usually made on the basis of rubber and various additives - from soot to silicon oxide) deforms. At the same time, small bumps that deform the tire do not affect the position of the wheel axis of rotation.

In case if the wheel propeller runs into more significant obstacles, then strong shocks cause increased deformation of the tire and a smooth movement of the axis of rotation of the wheel. The ability of a pneumatic tire to smoothly change the negative effect of road surface defects on the wheel axis of rotation is called smoothing.

The smoothing effect is provided by the elastic properties of the compressed air in the tire.

Note
When a part of the tire rolls out of contact with the road surface, a fraction of the energy, which is expended in deformation of the tire, is spent on internal friction in the rubber, turning into heat. Heating has a negative effect on the properties of tires, as a result - accelerated wear. Energy loss depends on tire design, internal air pressure, load, travel speed and transmitted torque. In case of an increase in the deformation of the tire, the losses for internal friction also increase. The consequence of this is an increase in the power, which is expended on the movement of the car. The air pressure in the tire must be increased in order to reduce deformation and irreversible losses. However, in order to meet the requirements for ensuring a high smoothing ability of the tire, on the one hand, and to reduce irreversible losses on internal friction, on the other, the air pressure in tires of each type is set taking into account their design features and operating conditions.

The air pressure in the tire of the wheel is the most important performance indicator. It is set by each manufacturer according to the design and intended purpose of the tire.

6.2.3 Wheel rim

Note
We are all used to talking about discs, about whether they are cast or forged - what are their markings. In fact, speaking of disks, we have always, even without knowing it, meant exactly the wheel, which includes a rim and a disk in its structure.

The wheel is usually mounted on a hub, which, in turn, is placed in a steering knuckle and rotates freely on roller bearings. A wheel is made out of sheet metal by stamping and subsequent welding of elements. Wheels can be cast from light-alloy materials (for example, aluminum and magnesium alloy), or they can be forged, which combine light alloy-material and stamping. Also, there are disc and discless wheels (remember the "unique" solution of such a wheel of the well-known "Tavria").

6.2.4 Pneumatic tire

6.2.5 Wheel arrangement

Note
It should be mentioned that at the moment tires are divided into two types: tube and tubeless. The tires of the first type have a special tube, into which air is pumped. In a tubeless tire, there is no such tube, and the tire is installed on the rim, compacted and inflated with air.

Figure 6.21 Arrangement of inflated tire.

6.2.5.a Rubber

The rubber, which is used for the production of tires consists of rubber (natural or synthetic), to which sulfur, soot, resin, chalk, recycled old rubber and other impurities and fillers are added. The tire consists of a tread, a cushion ply (with a belt), a carcass, sidewalls and sided beads with cores (force ring), as shown in the corresponding figure 6.21.

6.2.5.b Frame

The carcass serves as the basis of the tire. It connects all its parts into one whole and provides for the necessary rigidity, while it has high elasticity and strength. The frame is made of several layers of cord 1-1.5 mm thick. The number of cord layers is even in order to distribute the structural strength evenly and is usually 4 or 6 (for passenger car tires) and 6-14 (for truck and bus tires).

Interesting
With an increase in the number of layers of cord, the strength of the tire increases, but at the same time its mass increases and the rolling resistance increases, which is unacceptable.

6.2.5.c Cord

Cord is a special fabric, which consists mainly of longitudinal threads with a diameter of 0.6-0.8 mm with very rare transverse threads. Depending on the type and purpose of the tire, the cord can be cotton, viscose, nylon, perlon, nylon and metal. The cheapest of all is cotton cord. But it has the least strength, which, moreover, decreases significantly when the tire heats up.

The strength of nylon cord is approximately 2 times higher than that of cotton. And the strength of perlon and nylon cords is even higher. The most durable is a metal cord, the threads of which are twisted out of high-quality steel wire with a diameter of 0.15 mm. The strength of the metal cord is more than 10 times higher than that of the cotton cord, and it does not decrease when heated. Tires that are made out of such a cord have a small number of layers (1-4), less weight and rolling losses*. They are more durable. The cords are placed at a certain angle to the plane drawn through the axis of the wheel. The angle of inclination of the threads depends on the type and purpose of the tires. It is 50-52 ° for regular tires.

6.2.5.d Rolling loss

Note
* Rolling loss. Whatever one may say, but during movement, more precisely when rolling, friction arises in all layers of the tire. As a result of this the tire is deformed at first, as it were, with a delay, and then, with the same delay, it returns to its original position. As a result of this simple action, the tire starts heating up. And if it heats up, then it just spends part of the energy applied to it, which is intended for rolling, wasted. Scientists from many laboratories are studying the issues of this problem in order to reduce rolling losses.

6.2.5.e Cushion layer

The cushion ply (and breaker) bonds the tread to the carcass and protects it from impulses and shocks taken by the tread from road bumps. It usually consists of several layers of sparse rubberized cord, the thickness of the rubber layer in which is much greater than that of the carcass. The thickness of the cushion ply is 3-7 mm, and the number of cords depends on the type and purpose of the tire. Sidewalls protect the frame from damage and moisture.

6.2.5.f Sidewalls

Sidewalls protect the frame from damage and moisture.

They are usually made out of tread rubber with a thickness of 1.5-3.5 mm.

6.2.5.j Board

Beads help to keep the tire securely on the rim. Outside the bead there are one or two layers of rubberized tape, which protects them from abrasion on the rim and from damage during mounting and dismounting of the tire. Steel wire cores are located inside the beads. They increase the strength of the beads, and prevent them from stretching and prevent the tire from jumping off the wheel rim.

6.2.5.h Camera

The tube keeps the compressed air inside the tire. It is an elastic rubber shell in the form of a closed tube. For a tight fit (no wrinkles) inside the tire, the inner tube dimensions are slightly smaller than the inner cavity of the tire. Therefore, the air-filled tube is in a stretched state inside the tire. Tube wall thickness is usually 1.5-2.5 mm for passenger car tires and 2.5-5 mm for truck and bus tires. Radial grooves are made on the outer surface of the tube. They help evacuating the air, which remains between the tube and the tire after mounting the tire. Tubes are made out of high-strength rubber.

6.2.6 Tubeless tire features

The tubeless tire does not have a tube and rim tape and performs the functions of a tire and a tube at the same time. According to the arrangement, it is very close to a tube tire and in appearance it hardly differs from it. A feature of a tubeless tire is the availability of a sealing airtight rubber layer with a thickness of 1.5-3.5 mm on its inner surface.

Note
The material of the carcass of a tubeless tire is also characterized by high air resistance (since it uses viscose, kapron or nylon cord), which is 5-6 times higher than that of cotton cord.

Note
The tubeless tire has a reduced rim diameter and is mounted on a sealed rim.

6.2.7 Tread pattern

Attention
According to the traffic rules, it is forbidden to install tires of different sizes, designs and with different tread patterns on the same axle.

6.2.8 Protector purpose

Under ideal conditions, there should be no tread at all (look at the slicks of formula cars) in order to maximize the contact area between the tire and the road surface. However, ideal conditions are when the road is covered with asphalt concrete, moreover, dry one. As soon as even a small layer of liquid appears on the surface or the surface becomes simply wet, the grip* of the tire with the road will drop sharply, contact will be lost and the driver will lose control of the car. In order that when hitting a surface with a layer of water, this very water was where to drain (one might say, forcibly), the tire is replete with a herringbone tread. In case if the tire is intended for driving in winter, then the tread shape will also be appropriate - an increased number of sipes and dirt collectors.

Note
* The force with which the wheels "grab" the road is characterized by the coefficient of adhesion of the tires to the road. The coefficient of adhesion is the ratio of the adhesion force of the wheels to the road to the weight of the given wheel. Coefficient of adhesion with the road is essential when braking and accelerating a vehicle. The higher the coefficient of adhesion of the wheel, the higher will be the intensity of acceleration and braking of the car.

6.2.9 Tire tread patterns

• Non-directional (Figure 6.22) is a pattern, which is symmetrical about the vertical axis of the wheel passing through its axis of rotation. It is the most versatile, which is why most of the tires are produced with this pattern.
• Uni-directional (Figure 6.23) is a pattern, which is symmetrical with respect to the vertical axis passing through the central part of the tread. Its benefits include improved ability to drain water from the road contact patch and lower noise levels.
• Asymmetrical (Figure 6.24) is a pattern, which is asymmetrical about the vertical axis of the wheel. It is used for the implementation of various properties in one tire. For example, the outside of a tire performs better on dry roads, while the inside performs better on wet surfaces.

6.2.10 Tire marking

There are two concepts related to each tire model: standard size and indexes.

For example, the standard size is indicated as follows— 255/55 R16, where 255 – tire section width in millimeters;

55 – the ratio of the tire's section height (from the seat rim to the outer edge of the wheel) to the section width in percent;

R — radial cord structure, the composite cords in the carcass plies are radially arranged (directed from side to side);

16 — rim fit diameter in inches (1 inch = 2.54 cm).

The indices indicate the parameters of the maximum load per tire in kilograms and the speed rating - the maximum permissible speed in kilometers per hour, as well as additional indices that describe the properties of a particular tire.

Figure 6.25 Example of tire marking.

There are two types of markings: for tires of the domestic market and for foreign tires.

6.2.11 Marking of tires for domestic market

In accordance with GOST, the following mandatory inscriptions shall be applied to the tire:

• trade mark and (or) name of the manufacturer;
• name of the country of origin in English: "Made in ...";
• tire designation;
• trade mark (tire model);
• index of bearing capacity (carrying capacity);
• index of speed rating;
• "Tubeless" - for tubeless tires;
• "Reinforced" - for reinforced tires;
• "M + S" or "M.S" - for winter tires;
• "All seasons" - for all-season tires;
• date of manufacture, which consists of three digits: the first two indicate the week of manufacture, the last one - the year;
• "PSI" - pressure index from 20 to 85 (only for tires with the "C" index);
• "Regroovable" – in case if it is possible to deepen the tread pattern by cutting;
• approval mark "E" indicating the approval numbers and the country issuing the certificate;
• GOST number;
• national mark of conformity to GOST (it is allowed to apply only in the accompanying documentation);
• tire serial number;
• mark of the direction of rotation (in the case of a directional tread pattern);
• "TWI" - location of wear indicators;
• balancing mark (except for tires 6.50-16C and 215/90-15C supplied to operation);
• technical control stamp.

6.2.12 Foreign tire marking

Such tires may have other designations:

• "Тous terrain" - all-season;
• "R + W" (Road + Winter) - road + winter (universal);
• "Retread" – restored;
• "Inside" – inner side;
• "Outside" – outer side;
• "Rotation" - direction of rotation (for tires with uni-directional pattern);
• "Side facing inwards" - inner side (for asymmetric tires);
• "Side facing outwards" - the outer side (for asymmetric tires);
• "Steel" - designation of the presence of a steel cord;
• "TL" - tubeless tire;
• "TT" or "MIT SCHLAUCH" - tube tire.

6.2.13 RUN-FLAT tires

Run-flat technology is used in the production of expensive car tires. These tires have reinforced sidewalls. The availability of durable inserts in the sidewall of the tire made out of rubber of a special composition allows it to withstand the weight of the car even in a deflated state.

On a flat Run-flat tire, one can drive about 80 km in case if the car is fully loaded. In case if there is only a driver in the car, then you can drive on a flat tire for about 150 km (at a speed of no more than 80 km/h). The ability to drive at least 80 km on a flat tire without affecting the wheel and suspension allows drivers to avoid difficult and unsafe wheel changes in traffic. Engineers managed to ensure that this type of tire can be reused after vulcanization.

Figure 6.26 Tires with Run-flat technology.

Note
For safety reasons, run-flat tires can only be installed on vehicles with electronic stability control and tire pressure sensors that warn of changes in air pressure in them.

6.2.14 Wheel markings

Figure 6.27 Wheel.

It is useful to know the tire markings, since the tire is put on the rim, which also has its own marking, and it must correspond to the selected tire.

For example, the marking "8.5J x 17 H2 5/112 ET 35 d 66.6" on the wheel has the following decoding:

Note
The wheel designation is applied to the inner surface. It should be also duplicated on the packaging and be available in the accompanying documentation or stickers.

8.5 is wheel rim width in inches. The given size must necessarily correspond to the width of the tire;

Note
A tire with a width, which does not match the width of the wheel, may come off while driving.

x is a sign between the symbols for the width and the rim diameter, which indicates that the wheel rim is one-piece;

17 is the rim diameter of the wheel in inches, which must necessarily correspond to the rim diameter of the tire;

Note
Wheels with a diameter of 12 to 32 inches, the most common diameters are 14-16 inches, are used on passenger cars.

J is a coding letter, which informs about the design features of the rim flanges (inclination angles, radii of curvature, etc.);

Н2 — the letter "H" (abbreviation for the English word "Hump") indicates the availability of annular protrusions (so-called humps) on the shelves of the rim, which keep the tubeless tire from jumping off the wheel rim. Often there are two humps on the wheel (designation "H2"), but there can be one hump (designation "H"), they can have a flat shape (FH - "Flat Hump"), be asymmetric (AH - "Asymmetric Hump"), combined (CH - " Combi Hump ");

5/112 – PCD ("Pitch Circle Diameter" - the diameter formed by the centers of the holes for the wheel mounting). The number "5" indicates the number of mounting holes in the wheel for bolts or nuts (most commonly wheels have the number of mounting holes from 4 to 6, less often - 3, 8 or 10). "112" is the diameter of the circle formed by the centers of the mounting holes, in millimeters. There are a number of such diameters - for example, 98; 100; 112; 114.3; 120; 130; 139.7 and some others. Often they are used by manufacturers according to tradition or as the most suitable for vehicles for a particular purpose - for example, size 139.7 is typical for pickups and SUVs;

ET – designation of the size of the wheel disk offset in millimeters;

Note
Wheel disk offset (see figure 6.27) is the size between the seating (attachment) plane of the disk, which is adjacent to the wheel hub, and the axis of symmetry of the wheel rim. In case if the plane of contact with the wheel hub is “outside” with respect to the axis of symmetry, the overhang of the wheel disk is called positive, for example, ET35. In case if it is "from the inside" (closer to the car) - the offset is negative, for example, ET-20. Simply put, the more the wheel protrudes outside the body, the lower the offset value. In case if the offset designation is zero, then the contact surface with the wheel hub lies on the axis of symmetry of the wheel rim.

Note
Installing wheels with a reduced offset if compared to the standard offset can provide a different appearance of the car. However, such a turn of events can negatively affect both the handling and the life span of the wheel bearings.

d is hub diameter or center bore diameter in millimeters.

Noteе
In the best case, this diameter shall correspond to the diameter of the seat face on the hub.

Note
Always use only special bolts and nuts for securing the wheels.