MICHELIN

Technical Dictionary

Section width: The distance between the outside of a tyre’s sidewalls, not including any lettering or designs.
Series: Tyres with the same aspect ratio, or relationship of section height to section width.
Service description: Numbers and letters molded into the sidewall indicating the load-carrying capacity, load index, and the speed at which the tyre can carry a load under specified conditions, or the speed rating. Also known as load index and speed symbol.
Section height: The height of a tyre, measured from its rim to its outer tread.
Shimmy: Wobbling of wheels from side-to-side on a vehicle. Shimmying can be caused by a variety of factors, including improperly balanced tyres, poor alignment, and bent wheels.
Shoulder: The area of a tyre where the tread and sidewall meet.
Sidewall: That portion of a tyre between the tread and the bead. Protects the tyre against impacts with curbs, etc. This is also where the sidewall markings can be found which tell you important information regarding the tyre.
Silica: In 1992, Michelin discovered how to incorporate this new reinforcing filler into the rubber compound of tyres. The discovery paved the way for compounds that provided resistance to wear, low rolling resistance, and good road-holding.
Silica Tread Compound: A compounding of silica with a specially formulated synthetic elastomer for exceptional grip on cold and wet surfaces, as well as reliable durability.
Singles: One tyre mounted on each side of an axle (two tyres per axle).
Sipes: Special slits within a tread block that open as the tyre rolls into the contact patch then close, breaking the water tension on the road surface and putting rubber in contact with the road to maintain adhesion, increasing wet and snow traction.
Speed rating: An alphabetical code (A-Z) assigned to a tyre indicating the range of speeds at which the tyre can carry a load under specified service conditions.
Stability: Situation in which the driver maintains control of the vehicle.
Steering response: A vehicle’s reaction to a driver’s steering inputs. Also the feedback that drivers get through the steering wheel as they make steering inputs.
Steering system: The entyre mechanism that allows the driver to guide and direct the vehicle; includes the steering wheel, steering column, steering gear, linkages, and wheel supports.
Structure: The way in which a tyre carcass is constructed. Radial structure tyres can be identified by the word radial or by the letter R and today account for the majority of vehicle tyres.
Synthetic rubber: Man-made, as opposed to natural, rubber. Most of today’s passenger car and light truck tyres have a relatively small amount of natural rubber in their content.
Snow tyre: Also called winter tyre; a special type of tyre with a tread pattern and compound that gives better traction in snowy and icy conditions; identified by the M+S, M&S, or M/S on the sidewalls.
Suspension: The various springs, shock absorbers and linkages used to suspend a vehicle’s frame, body, engine, and drivetrain above its wheels.
Size: The combination of tyre width, construction type, aspect ratio, and rim size used in differentiating tyres.
Self-aligning torque: When the tyre is cornering, torque created at the road contact patch acts at a point somewhat to the rear of the actual wheel center due to pneumatic trail. This has the same effect as positive caster and tends to force the wheel back to the straight-ahead position.
Slip: The difference between the linear speed of the vehicle and the rotational speed of the tyre. For example, if a tyre is locked and sliding (e.g., not rotating) while the vehicle is still moving, then it is operating at -100% slip.
Slip angle: The difference between the direction the wheel is traveling and the direction the vehicle is traveling.
Squirm: Flexing of the tread blocks between the belt package and the road surface. Less squirm means better steering response; more squirm means worse steering response.
Standard load: The amount of weight a given size tyre can carry at a recommended air pressure.
Star pattern: A pattern for tightening the lug nuts when mounting the tyre and wheel assembly to the vehicle. This pattern assures uniform pressure, prevents misalignment, and helps keep the wheel centered.
Static balance: Exists when the weight mass is evenly distributed around the axis of rotation. Static imbalance can be detected from vibrations through the seat, floor and steering column.
Static loaded radius: Distance from the wheel axis of rotation to supporting surface at a given load and stated inflation pressure.
Step groove: A design feature at the base of the groove that generates an additional gripping mechanism in deeper snow.
Stress Equilibrium Casing™: A radial casing design that more evenly distributes the forces of acceleration, cornering, and braking throughout the contact patch, allowing for design enhancements in the shoulder and the use of softer, better gripping compounds.
Supporting Knobs Technology: Small bumps in the shoulder grooves help to provide lateral block rigidity.
Symmetrical Tread Design: Uniform tread pattern on both sides of the tread for better performance in specific conditions and on specific roads.
Steel belt: The combination of steel cords covered with rubber that forms a strip or belt placed under the tread rubber and on top of the casing (carcass); ensures uniformity when the tyre is rotating and helps prevent flats.