Technical Dictionary

Section height

The height of a tyre, measured from its rim to its outer tread.

Section width

The distance between the outside of a tyre’s sidewalls, not including any lettering or designs.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Supporting Knobs Technology

Small bumps in the shoulder grooves help to provide lateral block rigidity.

Suspension

The various springs, shock absorbers and linkages used to suspend a vehicle’s frame, body, engine, and drivetrain above its wheels.

Symmetrical Tread Design

Uniform tread pattern on both sides of the tread for better performance in specific conditions and on specific roads.

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.