STRUCTURE OF A MOTORCYCLE TIRES
BIAS tire THE MOST POPULAR MOTORCYCLE RIMS
Also indicated as conventional or x-ply tire. The structure of this tire is made of a carcass where, depending on the different speed and load specifications, one or more layers are overlapoverlapped. Each layer is made of textile cords coated into rubber and the overlap angle is designed in order to confer the tire the required dynamic characteristics.
The structure of those tyres is realized with a conventional carcass and a belt made of one or more crossed layers. The difference between carcass and belt is given by the different goals that they have to fulfil and consequently the different materials that are used: the belt is mainly made by Nylon and has to reduce the dynamic deformation due to the centrifugal forces, while the carcass has to mainly give the tire its contour.
BELTED TIRE WITH RADIAL CARCASS (90°)
The main difference towards the bias-belted tyre is given by the structure of the carcass that in this case is radial. This means that its cords are wrapped radially around the tyre, means from one shoulder to the other. In this way low-section tyres can be realized, giving big advantages in terms of cornering stability, reduced weight and high-speed performance.
0°-STEEL BELTED TIRE WITH RADIAL CARCASS (90°)
Patented technology by Metzeler realizing the structure of both front and rear tyre using a radial carcass and a single layer belt made of steel. Considering the rolling direction of the tyre, the belt is winded circumferentially around the carcass giving an angle close to 0°. The advantages coming from the use of steel are its extremely high rigidity and the possibility to tune the winding spacing giving a differentiated stiffness distribution from shoulder to crown.
TREAD PATTERN AND COMPOUND
The tread pattern is the outer part of the tyre, in contact with the road. The profile and rubber compound are chosen based on the use of the tyre. In general with a harder rubber compound mileage increases, and grip decreases. The softer the rubber compound, the more grip a tyre has, but the mileage is reduced. Of course, mileage depends also and greatly on the average speed driven and on the asphalt conditions.
The carcass is the basis of the whole system and gives the tyre its form. The materials used are one or more plies of Nylon or Rayon or Polyester. The carcass supports the load of the motorcycle, ensures stability and contributes to comfort . The carcass must allow some deformation to absorb road shock. Radial carcasses are more flexible than traditional bias-ply construction and thus offer superior damping.
This is the component by which the tyre is fitted on the rim. It is reinforced by steel cords coated in rubber. They aid in transmitting the accelerating and braking torques, as well as to mechanically connect the tyre to the rim and to ensure against loss of inflation pressure.
The speed index (SI) indicates the maximum speed the tyre is homologated for. Tyres can have the same pattern and size, but a different speed rating, this is due to the tyre construction and therefore they will perform differently. Maximum speed capability varies from size to size. You should pay attention to the recommendations for your motorcycle.
Tyres are offered in different load carrying capacities. It is extremely important not to exceed the max. load rating. You must take the weight of the motorcycle, the weight of any optional equipment, as well as the weight of a passenger into consideration before determining what the "Load Capacity" of your tyres should be. A tyre's load carrying ability can be reduced by underinflation. Before travelling, you must calculate the total weight (luggage, equipment, passengers) to be added to the motorcycle.
Tubeless tyres require a special bead seat, because the beads have to form an airtight seal on the rim. Not all cast wheels, aluminium or magnesium, are suitable for tubeless tyre fitment. Do not mount tyres without tubes, unless the wheel manufacturer recommends it. If a tube is inserted, it is then possible to fit a tube-less tyre to a tubetype rim.
Centrifugal forces work on the valve stem. At high speeds they have the same effect as pushing on the valve with your finger. The tyre can deflate. The valve cap is the only part preventing it. Normally this phenomenon happens only at very high speeds. But an old or low quality valve stem can open at speeds lower than 200 km/h. Therefore the cap should always be tightly closed.
The name given to PIRELLI street tread compounds designed for competition use. One of the features of the PIRELLI Corsa is a much higher level of grip in comparison to the standard tyres.
Abbreviation for ”motorcycle”. This marking is to ensure there is no confusion when mounting motorcycle tyres of similiar rim diameter to automobile tyres. Motorcycle tyres must not be mounted on automobile rims as there are important differences between motorcycle and automobile rims.
The abbreviation for "Not for Highway service". Motorcycle tyres with this marking are only for racing or off road purposes cannot be used on public roads.
(abbreviation rf. or reinf.) refers to the construction of a tyre, increasing its load capacity.
Abbreviation for tubeless. Tyres with this indication, when fitted to a tubeless type rim do not require a tube.
Abbreviation for tubetype. Tyres with this indication must have a tube installed.
Treadwear indicator, indicates minimum level of tread depth for safe use. However many countries have different regulations regarding minimum tread depth.
The sidewall is the "name plate" of a tyre. The combinations of numbers and letters indicate not only the name of the tyre but also the maximum speed and load allowed. In the transmission of ircumferencial and side forces, as well as bump absorption the side wall plays an important role.
REPLACING A WORN TYRE
Remember, precise matching of front and rear tyres is necessary to obtain optimum performance and handling. When fitting a new front tyre, check the wear on the rear tyre. A new front tyre combinde with worn rear tyre may cause instability. Please bear in mind that many other factors can affect the hand-ling of a motorcycle, including the weight and height of the rider, and the addition of luggage of fairings. Please consult the motorcycle manufacturer before making nonstandard modifications.
TYRE MOUNTING - IMPORTANT INFORMATION
These tyres are only to be used on vehicles for which motorcycle tyres were originally stipulated by the manufacturer. Any other use can be dangerous. Check if the tyre has directional arrows. If it does, you must mount the tyre so that the arrow points in the direction of rotation. Some PIRELLI tyres have a red dot on the sidewall. This indicates the lightest point, and should be positioned next to the valve. To clean or lubricate the bead, use tyre mounting lubricant or soapy water. To seat the bead: remove the valve stem core and inflate the tyre. For safety reasons do not inflate motorcycle tyres to more than 50 psi (3,5 bar); for scooters tyres do not exceed 150 % of the indicated maximum pressure. Be sure to reinstall the valve stem core and inflate the tyre/tube to the recommended riding pres-sure. Check the bead control lines for proper seating. If the beads are not properly seated, you will have to deflate the tyres/tubes and repeat the above procedure.
FUNCTIONS OF A MOTORCYCLE TIRE
Today, the level of technology in tyres and motorcycles is extremely high. Riders often forget that the tyre is the only point of contact between the bike and the ground, and that it must perform multiple tasks including steering, carrying a load, absorbing road shock, rolling smoothly, transmitting mechanical inputs, and wearing evenly.
STEERING: The tyre must steer predictably, regardless of the road or weather conditions. The motorcycle’s trajectory depends on the directional stability of the tyre. The tyre should transmit steering inputs without drifting off the intended line. Every bike has a specific recommended inflation pressure for each wheel. Correctly adjusting pressure for both front and rear tyres helps ensure steering stability and precision.
LOAD CARRYING: The tyre supports the bike at a standstill and while in motion, but must also withstand considerable load transfers during acceleration and braking.
SHOCK ABSORBING: Tyres roll over obstacles and damp road shocks, ensuring the rider’s and passenger’s comfort as well as protecting the bike. The tyre’s greatest asset is its flexibility, particularly in a vertical plane. The elasticity of the air inside the tyre helps it to absorb shocks from obstacles and irregularities in the road. The correct pressure thus helps achieve a desirable level of comfort as well as accurate steering.
ROLLING EFFICIENCY: Tyres should roll smoothly with minimal rolling resistance for a feeling of control and with steady, progressive wear.
MECHANICAL GRIP: Tyres transmit the bike’s mechanical forces of horsepower and braking. The few square centimetres that constitute the contact patch can make all the difference in a bike’s performance.
WEARING: Tyres need to maintain a dependable level of performance throughout millions of revolutions. Tyre wear depends on many factors (load, speed, condition of the road, vehicle maintenance, riding style...) but especially the quality of the contact patch. Air pressure plays a major role, affecting:
• the size and shape of the contact patch,
• the distribution of the mechanical forces on various points of the tyre in contact with the road.
These six functions determine a tyre’s safety, comfort and economy. You expect them to be present throughout the lifespan of the tyre, but you must take certain precautions. The tyre needs air to perform and to last, so it’s necessary to check inflation pressure regularly. Every tyre loses air, molecule by molecule, because of rubber’s natural porosity. Accidental causes such as valve or rim damage often accelerate air loss, as will small cuts in the tyre tread or sidewall. Air pressure affects every aspect of the tyre: safety, economy and riding enjoyment. The wrong pressure can degrade performance in all areas.Routine pressure checks can prevent many worries.