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TKART magazine How To | To make a tire for karting
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08 June 2017
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Ever more determinant in today’s motorsports, tires are fruit of constant research, high technology, thousands of kilometers worth of tests, and a myriad of materials... With the help of Le Cont, the Italian producer headed by brothers Valter and Sergio Cont, we unveil the “perfect” tire recipe
the starting point of tire manufacturing are fabric cords: manufacturers choose textiles based on the desired features of the final product. Before being bonded with the rubber compound that forms the actual tire tread, the fabric cords are pre-treated with a thin layer of adhesive rubber (only the big tire manufacturers do this operation in-house; smaller companies receive the fabric cord already finished) and are then cut into large diamond-shaped pieces. This elements, together with bead wire loops and bead filler “wedges”, form the “carcass” or the basic structure of the tire. Once the sides are reinforced with a thin layer of rubber to form the sidewall, the structure is then covered in tread, which (like the bead filler and the sidewall) is made of a rubber compound specifically formulated to yield the desired performance features.
Fabric chord: the most common fabrics used in kart tire production are made of polyester , nylon, and (less often) rayon: the first generally for “slicks” and the others usually for “rain” tires. Double or triple-ply, fabric cords differ by weave density. Since the choice of fabrics influences the behavior of the final product, some of the major manufactuers have their textiles custom-engineered with specific characteristics.
Bead wire loops: the bead wire loop is also formed by several strings (generally 4 or 5) of steel wire woven together, covered by rubber, and wound into 5 inch loops (12.7 cm): the size corresponds to the diameter of the tire rim.
Bead filler: in shop-talk they are referred to as “wedges”: they are pieces of hard rubber compound (different compounds are used for front and rear tires) that are “extruded” to form cusps. Their purpose is to reinforce the tire “shoulder”.
Three elements play an even role inside the Banbury, the machine that mixes together the various ingredients of the rubber compound. The first in line are polymers (in the form of paste or grains), which include natural rubber and synthetics derived from hydrocarbons. A great deal of tire research and development is concerned with finding the best polymers for every given type of compound, but also figuring out how to get the same quality mesh starting from less expensive polymer solutions.
The second ingredient is carbon black, a synthetic material obtained from petrolium that takes the form of small grains. Once these are pulverized by the Banbury, it’s time to feed oils into the mixer. Oils are basically of three kinds: aromatic, naphtenic, and paraffinic, breakdown further into smaller subdivisions based on viscosity.
Polymers: they constitute about 30% of a given tire compound. They may be used individually or in “formulas” of up to 5 different kinds. There are thousands of varieties available and a company like Le Cont uses up to 150 different varieties for its various productions.
Carbon Black: this material accounts for another 30% of the final tread compound. It is extremely potent: one gram is enough to blacken a surface area of 18 square meters! Besides determining the color of a tire, it also inluences its brasiveness, durability, and hardness. As a general rule of thumb, the more carbon black, the harder the tire.
Oils: also amounting to 30% of the compound mix, they are added in different combinations depending on the desired characteristics. For instance, Le Cont uses 22 different oils, mixing them as needed (but never all together). Oils influence tire grip the opposite way comapred to carbon black: the more oil is mixed in, the softer the compound.
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