Contents.IntroductionTire thread designTypes of tiresManufacturing of threadsPerformance characteristicsProblems with tiresThread depth and the lawMeasuring the depth of the threadThread typesProbable causes of thread failureConclusion

IntroductionTyres have a range of functions providing grip, steering and

braking. The average sized tyre will rotate about 880 times every mile, this means that during its life the tyre will rotate more than 26 million times. Each time it is in contact with the road it is deflected under the load of the vehicle, meaning it is distorted more times than most other vehicle components

Tyres have tread for traction and to displace water on a wet road. Without tread on a tyre you would have to run tyres with an extremely soft compound construction in order to have traction. This type tyre would not last very long and would hydroplane on a wet road. Race cars run tires without tread on dry racetracks. These type tyres have a very soft compound with excellent traction but are only meant to last around 100-200 miles.

TYRE THREAD DESIGN

Fig. 1. Cross section of radial tread in a passenger tyre: 1 - inner-liner, 2 - carcass material, 3 - bead wire (core), 4 - apex, 5 - tyre strip, 6 - rim (bead) strip, 7 - sidewall, 8 - breaker strip, 9 - PA breaker strip, 10 – tread

The tyre tread (Figure 1) is a part of tyre that which is in direct contact of a vehicle with the road and thus, it is responsible for driving force transfer. The wear of the tyre tread of passenger cars and trucks travelling on common roads is characterised by its abrasion. The tread of a car tyre is disposed towards abrasive effect of the road.

Groove:- The groove is the hollow part or the tyre tread. The grooves are cut which makes the tyres pattern. Tyre come in different patterns and grooves, from the simple block pattern to the modern v tread designs. The hollow part of the tyre (the groove) is designed to channel the water out of the tyre. As a tyre wears the groove becomes less hollow and apparent. The design of the groove effects the tyre performance and the quality of the tyre.

Pitch:- The pitch/cuff is the small tread at the edge of both sides of the tyres as shown in the picture in the left. The pitch often wears out before the wrest of the tyre. The function of the pitch is to enhance the performance providing better steering and stability. This pitch is mostly visible on winter tyres on these tyres the pitch functions to byte the road to grip the ice.

Rib shape:- As the name implies the design of this pattern is like a rib shape with the grooves running from the centre to the edges like a rib pattern. The pattern aids faster water drainage and hence gives good traction on wet roads. This pattern is commonly found on most tyres and in today’s high speed driving is suitable for all car types. The thing that puts most people of this type of design is that they are often rotational tyres meaning the tyre direction has to be set when mounting the tyre. Meaning a tyre on the left side cannot go on the

right side.Zigzag shape:- This is a classic design for a van tyre. Even today most van tyres bar a few are still using this zigzag design. The reason for the success of this design in commercial use is because of the grooves that are cut in a zigzag giving the tyre low rolling resistance, low heat generation ideal for the long journeys that commercial vehicles do. There are many disadvantages of this type of pattern including poor cornering because of flex in the tyre, also lack of grip in wet and dry traction.

Asymmetric pattern:- Asymmetric tyres haven a different tread design on the inside to the outside of the tyre. An asymmetric looks like to different tyres joined in the middle. The sides differ in pattern to give different functionality and the inside offers better cornering traction while the outside is designed to channel water away. This type of design is commonly found on high performance vehicles more commonly on the wider tyres. Often people confuse a rotation tyre with an asymmetric pattern tyre unlike a rotation tyre an asymmetric tyres have a inside and outside marking and unlike rotation tyres can be mounted on the car on the left or the right.

Block shape:- This type of pattern as the name suggests has a block shape design. The grooves are very small the tyre pattern is very tight and close. The advances in tyre designs has seen this tyre less in use it was widely used on passenger cars up to 90’s today it is only seen on winter and all season type tyres. This type of pattern is ideally suited for winter conditions and hence is mostly seen on winter all season tyres.

 

TYPES OF TYRESSlick tyresR compound tyres (grooved slicks)Bicycle tyresStreet tiresOff-road tires

SLICK TYRES Slick tyres are not suitable for use on common road vehicles,

which must be able to operate in all weather conditions. They are used in auto racing where competitors can choose different tyres based on the weather conditions and can often change tyres during a race. Slick tires provide far more traction than grooved tyres on dry roads, due to their greater contact area but typically have far less traction than grooved tyres under wet conditions. Wet roads severely diminish the traction because of aquaplaning due to water trapped between the tyre contact area and the road surface. Grooved tyres are designed to remove water from the contact area through the grooves, thereby maintaining traction even in wet conditions.

R compound tyres (grooved slicks)The development in cheater slick technology has affected

the development of tyres for racing series other than drag racing as well. When other forms of auto racing similarly instituted classes which require DOT approved street tyres, some manufacturers similarly began to market tyres which superficially resembled their high performance street tyres, but with the least tread permissible and with very soft, sticky rubber, intended specifically for competition because the soft tread would wear too quickly for street use. These became known, loosely, as R compound tyres. With additional years of progress, this class of tyre has in its turn followed its own line of development, to the point where they have little in common with true street tyres of the same brand. Ironically, this has led to new classes of racing which require not only DOT approval, but also a minimum tread wear rating, in an effort to eliminate the R compound tyres from competition and require "true" street tyres.

Bicycle tyresIn contrast, many bicycle tyres made for street use are

slick. Aquaplaning does not present a problem for bicycles due to their narrower width, higher pressure, lower speed, and circular cross section (due to the need to lean the bicycle in turns), the bicycle tyre can penetrate the water layer to contact the road much more easily; in practice, grooved bicycle tyres do not outperform slick tyres on wet roads. However, many low and medium performance bicycle tyres have substantial tread depth, because the bicycles are designed with off-road excursions in mind, in dirt, gravel, or sand the tread provides significantly improved traction

Street tiresThe grooves in the rubber are designed to allow water to be

expelled from beneath the tire and prevent hydroplaning. The proportion of rubber to air space on the road surface directly affects its traction. Design of tire tread has an impact upon noise generated, especially at freeway speeds. Generally there is a tradeoff of tread friction capability; deeper patterns often enhance safety, but simpler designs are less costly to produce and actually may afford some roadway noise mitigation. Tires intended for dry weather use will be designed with minimal pattern to increase the contact patch. Tires without any tread patterns are known as slicks and are generally used for racing only, since they are quite dangerous if the road surface is wet.

Off-road tires

Off road tyres used in mud or dirt feature individual knob patterns to allow the tire to bite into the surface and lever the sides of the tread to get a better grip. Given the smaller contact patch, these tires tend to wear quickly when used on asphalt.

Manufacturing of threads

the stock is destined for tire treads, sidewall or bead filler, it is taken by means of conveyors to the extruder, or tuber, where warmed stock is fed into the barrel mouth and forced by screw into the head and out through a die. The die has been carefully made to obtain the shape and thickness desired by the tire designers. From the tuber, the treads are sent to the skiver where they are cut to exact lengths for use in tire building.

If the stock is to be used in the carcass of the tire, it is sent to the calendar. Tire cord fabrics, cushion stock, and the inner-liner stock are all prepared at the calendar. Nylon, polyester, Fiberglass, steel, Kevlar, and rayon cord is purchased already coated with an adhesive to give a better bond between the rubber and the cord.

The adhesive treated fabric then goes through another process called calendaring where rubber is squeezed around the cords to insulate them from each other and make heat-resistant tire plies. The rubberized fabric is cut mechanically on a bias cutter into the proper angle and sized ply strips. In the tire building operation, these are laid at alternating angles, or biased angles, to give the tire body maximum strength. The angle chosen by the tire engineers is aimed to meet the verifying requirements of comfort, inflation and driving stresses

Performance characteristics

Dry traction Dry traction is measure of the tire’s ability to deliver traction, or grip, under dry conditions. Dry traction increases in proportion to the tread contact area. Dry traction is also a function of the tackiness of the rubber compound.

Wet traction Wet traction is measure of the tire's ability to deliver traction, or grip, under wet conditions. Wet traction is improved by the tread design's ability to channel water out of the tire footprint and reduce hydroplaning. However, tires with a circular cross-section, such as those found on racing bicycles and motorcycles, when properly inflated have a sufficiently small footprint to not be susceptible to hydroplaning. For such tires, it is observed that fully slick tires will give superior traction on both wet and dry pavement

Problems With Tires

The wear patterns of an underinflated, properly inflated and overinflated tire

Under inflation can cause tires to wear more on the outside than the inside. It also causes reduced fuel efficiency and increased heat buildup in the tires. It is important to check the tire pressure with a gauge at least once a month.

Over inflation causes tires to wear more in the center of the tread. The tire pressure should never exceed the maximum that is listed on the side of the tire. Car manufacturers often suggest a lower pressure than the maximum because the tires will give a softer ride. But running the tires at a higher pressure will improve mileage.

Misalignment of the wheels causes either the inside or the outside to wear unevenly, or to have a rough, slightly torn appearance.

Tread Depth and the Law

Most car type tires have tread wear indicators, usually at least six small ribs across the bottom of the main tread grooves, and when the tread surface becomes level with these ribs the tire is at the legal limit and must be replaced.

MEASURING THE DEPTH OF TREADThere are two methods of measuringCoin method Tread depth gauge

Coin methodPlace a penny into several tread grooves

across the tire. If part of Lincoln's head is always covered by the tread, you have more than 2/32" of tread depth remaining.

Place a quarter into several tread grooves across the tire. If part of Washington's head is always covered by the tread, you have more than 4/32" of tread depth remaining.

Place a quarter into several tread grooves across the tire. If part of Washington's head is always covered by the tread, you have more than 4/32" of tread depth remaining.

Place a penny into several tread grooves across the tire. If the top of the Lincoln Memorial is always covered by the tread, you have more than 6/32" of tread depth remaining.

Once you have determined the approximate remaining tread depth in the first location, you can complete your measurement of each tire by placing the coin into additional locations at lease 15 inches apart around the tire's central circumferential groove, as well as in its inner and outer grooves. This will help detect uneven wear caused by mechanical or service conditions

STEP 1Confirm which measuring scale you are using.

Some tread depthgauges measure in 32nds of an inch (left), while others measure inboth 32nds of an inch and millimeters (right).

STEP 2Push the tread depth gauge against a hard, flat

surface to confirm it"zeros out" when fully compressed.

Tread depth gauge

STEP 3Place the probe into the center of a

circumferential tire groove and push down on the gauge's base.

STEP 4Do not place the probe on the molded tread

wear indicators or on any raised surfaces of the tread design.

STEP 5Carefully remove gauge by holding its barrel

(without touching theprobe) and confirm the tread depth reading.

STEP 6: Place the probe into additional locations around the central circumferential tire groove at lease 15 inches apart and repeat.

STEP 7: Place the probe into the inner and outer circumferential grooves and repeat.

STEP 8: Average all readings.STEP 9: Identify the percentage of tire wear by confirming the

tire's original/new tread depth in its specs compared to the remaining tread depth just measured.

Tread typesIt is most common for the tyres on all four wheels to have the

same tread pattern. This means they are interchangeable and can be fitted on any of the vehicle’s wheels. However you can also have the following types of tread pattern, which are the most common on modern tyres:

Multi directional patterns are the most convenient and flexible to use. They can be fitted in any position on the vehicle and any way round on the wheel.

Asymmetric – Fits any wheel but must be placed correct way round. Offers better compromise between wet and dry performance.

Directional – Must travel in the direction of the arrow on the tyre. Offer higher straight-line stability, better resistance to aquaplaning and is potentially quieter.

Cold weather tyres – May be of any tread pattern but the tread blocks contain many small grooves called sips, which help disperse water and provide additional grip on snow and ice. A different rubber compound is also used allowing the tyre to remain flexible at low temperatures. When combined with the advanced tread design this provides much higher levels of grip when the temperature is below 7oC and a safer drive

Probable causes of tread failuresIrregular tread wear – One shoulder

Description:Excessive wear on ONE shoulder around the circumference of the tyre.

Probable Causes:Axle geometry

Axles not parallel.Incorrect wheel alignment.Excessive toe-in or toe-out.

Suggested Actions:Check wheel and axle alignment. Check suspension system.

Irregular tread wear – Both shoulders

Description:Excessive wear on BOTH shoulders around the circumference of the tyre.

Probable Causes:Incorrect tyre inflation pressure.

Under inflation.

Suggested Actions:Look for reason of under inflation (defective valve, accidental damage or puncture, defective repair, etc.).Check vehicle manufacturers recommended inflation pressures.

Irregular tread wear - Centre

Description:Excessive wear in central tread area around the circumference of the tyre. Characteristic of rear drive axle fitment.

Probable Causes:Incorrect tyre inflation pressure.

Over inflation.

Suggested Actions:Check vehicle manufacturers recommended inflation pressures

Tread separation Description:Separation of tread rubber from carcass.

Probable Causes:Under inflation causing excessive flexing and heat generation leading deterioration of rubber bonding.Overloading.Incorrect application.Accidental damage to tread area resulting in water/dust penetration.

Suggested Actions:Remove tyre from service.Check inflation pressures.Check tyre size, load / speed correspond to manufacturers specification

Accidental tread impact damage

DESCRIPTION:DISINTEGRATION OF TYRE STRUCTURE.

PROBABLE CAUSES:VIOLENT IMPACT WITH ROAD OBSTACLE (EG. LARGE ROCK, POT HOLE, ETC.).

HIGH SPEED IMPACT.OVER INFLATION.

SUGGESTED ACTIONS:REMOVE TYRE FROM SERVICE.CHECK INFLATION PRESSURE CORRESPONDS TO VEHICLE MANUFACTURERS RECOMMENDATION

 Conclusion

From the above paper it can be concluded that, by using tires with different tread patterns in different weather or working conditions traction can be increased and also the tyre wear can be reduced and also better control and stability of the vehicle is achieved.