At Tyre King we know that not everyone is a tyre expert and that buying tyres can involve a lot of jargon. We aim to make buying tyres as simple and straightforward as possible and that is why we’ve created this easy to use glossary of terms.
Alternatively, please call one of our tyre experts on 0800 1 600 600 who would be more than happy to help with any queries you may have.
If there is any jargon you need clarified and is not listed in our glossary, please let us know and one of our tyre experts will endeavor to translate it for you.
Air Pressure: This is essentially the volume of air inside the tyre, it can be measured in either pounds per square inch PSI or Bar. Having the correct pressure for tyres is a key factor in Tyre Safety and can usually be found in the Vehicle handbook as well as the fuel cap flap.
Alignment: This is essentially the correct vertical alignment of the tyres. Generally describes the checks and corrects made to the suspension and steering systems of the vehicle to ensure compliance with the manufacturers recommendations
Alloy Wheels: Alloy wheels differ from normal Steel wheels because of their lighter weight, which improves the steering and the speed of the car. Alloy wheels are also better heat conductors than steel wheels, improving heat dissipation from the brakes, which reduces the chance of brake failure in more demanding driving conditions
All Season Tyres: Tyres designed to be used in all weathers all year round
Aquaplaning: The vehicle rides on a layer/film of water above the road surface and not the road itself. This causes traction loss and loss of control. Vehicle often can feel unresponsive and the back of the vehicle may weave or wobble. If this occurs, , put on your Hazard warning lights, avoid braking or accelerating, depress the clutch, keep a strong firm grip of the steering wheel, steer where you want to go (into the skid) and try not to stay calm.
Aspect Ratio: (also referred to as Profile) Expression of a tyres height as a percentage of its section width, for example if the width was 300mm and the height was 150mm the aspect ratio would be 50%.
Asymmetric: (also see Profile) When the tyre tread pattern varies from one side of the tread to the other. These must be fitted with the outside sidewall on the outer face of the wheel. Directional versions will also be specific to the left and right sides of the vehicle. This information is often indicated on the sidewall.
Balancing: This is the process for compensating for slight variations in tyre and wheel assembly. By ensuring weight is equally distributed when the tyres and wheels spin, any abnormal vibrations can be eliminated.
Bar: Metric Unit for measuring Air Pressure (1 bar = 14.5037738 psi)
Bead: a multi-layer steel ring that helps to hold the tyre to the rim. This bead ensures adequate contact pressure between the tyre and the rim, the bead ensures air seal.
Bead wires: This is a coil of high tensile steel wire treated to improve bonding when encased in a “matrix” of hard rubber. The casing plies are turned around the bead and are securely bonded to the structure when the tyre is cured
Blades: (also known as Sipes): this refers to slits in the tread blocks which are designed to increase grip on wet-weather tyres by moving water away from the tyre.
Budget Tyres(also see Economy Tyres): Tyres which retail cheaper than mid range tyres, it will follow these tyres will not perform as well.
Casing: Consisting of Ply, bead area and belts, this is the skeleton of the tyre sitting underneath the tread and sidewalls. Also referred to as the Carcass.
Camber: When the vehicle is at its normal ride level, the deviance from the vertical of the tyre centre line. May cause uneven tyre wear if incorrect.
Centre-less Alloys: Standard alloys designed by Citroen and Peugeot who with no centre on them. This means the garage will need a specialist adaptor to balance the tyre when fitted. This adaptor fits directly into were the alloy studs go. Not all fitting centres can fit tyres on this type of wheel.
Cold Inflation Pressure: Tyre pressure before the tyre has been heated up from driving.
Cold Weather Tyres: (also see Winter Tyres) These Tyres are designed to give better grip in temperatures of below 7 degrees. (Note that Snow Tyres are something different in you are ever driving overseas).
Contact Patch: (also see Footprint) Tyre area in contact with the road. This varies depending on tyre construction, the compounds, tread design and tyre pressure.
Directional Tyres: (also see asymmetric): This type of tyre must be fitted in an indicated orientation. Chevron or arrow shaped patterns are often used to help remove water from under the tyre.
Economy Tyres: (budget tyres) New tyres of fair quality which retail cheaper than mid range tyres (link). As you would expect performance will also be lower.
Footprint: (also see Contact Patch): The area of tyre tread that is in contact with the road surface.
Hysteresis: In reference to Actions and reactions: not all energy applied to a tyre is dispersed. When dealing with an elastic material like rubber energy is always absorbed and this creates heat build-up.
Inner Liner The layer of rubber inside a tubeless tyre which stops air seeping out of the tyre during normal use.
Load Index: Indicated on the Tyre Wall a standardized numerical guide that indicates the maximum weight a tyre can carry at the speed specified by its speed rating under conditions specified by the manufacturer.
Low Profile Tyres: These are tyres with shallow sidewalls usually fitted to high performance vehicles
Maximum Inflation pressure: Exactly what it says, the maximum pressure a tyre can be inflated too.
Mid Range Tyres: Tyres which retail at a lower price than premium brands the performance of this range shall logically be lower
“Mini” Spare: (also known as A Space Saving tyre): Smaller than the road tyres, this type of tyre is designed to save space and reduce weight in the vehicle. A temporary measure to get you home these tyres should be changed as soon as possible, these tyres also have a lower maximum speed.
“M+S” Tyre: Tyres which have been designed to perform better in Mud and Snow
Nominal Section Width: The section width of an inflated tyre mounted on its theoretical rim and indicated in the tyre size designation.
Nominal Rim Diameter: A size code figure for reference purposes only, as indicated in the tyre and rim size designation.
Original Equipment (OE): This is the original brand of tyre that was fitted by the car manufacturer. Please not that there may be more than one OE brand fitment.
Oversteer (see also Understeer): This is a term used to describe a loss of grip to the rear wheels during cornering causing the car to slide sideways.
Plies: The reinforcing members of a tyre which are composed of layers of cord fabric and rubber that provide the strength to contain the air pressure needed to support a load and resist deflection.
Profile: (also see aspect ratio) The height of the tyre sidewall expressed as a percentage of the tyres width.
PSI(pounds per square inch) : Imperial measurement unit for air pressure
Radial Tyre: The design of all modern car tyres. Development of the use of parallel carcass belts for sidewalls and crossed belts for the crown of the tyre.
Repairable Area: Tyre Tread area where a puncture repair can be made to a recommended International Standard.
Reinforced Tyres: Tyre where the manufacturer has added extra strength by adding more Plies into the side wall to handle more weight e.g. for heavier vehicles. (i.e SAAB 9-3s or Ford Galaxy’s Renault Laguna)
Remoulding: A recycling process where a tyre is buffed back to its casing, repaired and rebuilt using a fresh tread compound
Retreading: This is the process of replacing the tread layer on a tyre. Usually reserved for commercial, agricultural and industrial tyres
Rim: The metal edge of the wheel on which the bead is seated supporting the tyre
Rim Size: The diameter of the rim (usually measured in inches and also known as the wheel size)
Rim Width: the Distance between the 2 opposite inside edges of the rim flanges
Rolling Resistance: The energy required to keep a tyre moving at a constant speed. The lower the rolling resistance the less energy being used to keep the tyre moving.
Run-Flat: Tyres which allow a driver to continue a journey in the event of low or no pressure. Please note that Run flats are designed to run for short distances and should be replaced as soon as possible
Section Height: The height of the tyre from the rim to the outer tread
Section Width: Measurement of the tyre from side to side. This measurement excludes raised letters or any other additional sidewall items
Service description: As well as Tyre Size Designation a tyre may be identified by a Service Description consisting of a load index (or two Load Indices in the case of single/dual fitments) and a Speed Symbol.
Shoulder: This is where the sidewall and the tread meet on the tyre
Sidewall: This refers to the area between the (bead and the start of the tread (link)
Silica: reinforcing filler used in a rubber compound to provide higher tyre mileage and lower Rolling Resistance
Sipes: (also known as Blades) this refers to slits in the tread blocks which are designed to increase grip on winter and wet-weather tyres by moving water away from the tyre.
Snow Tyres: Tyres specifically designed to perform better in the snow
Space Saving Tyre: (also known as a “Mini” tyre): Smaller than the road tyres, this type of Tyre is designed to save space and reduce weight in the vehicle. A temporary measure to get you home these tyres should be changed as soon as possible, these tyres also have a lower maximum speed.
Speed Rating: The standardized index which is used to indicate the maximum speed a tyre can sustain carrying the
Specified load in the load index under the conditions specified by the tyre manufacturer.
Steel rimmed wheels: The standard fit wheel for most cars, can be upgraded to alloy wheels
Traction: A term used to describe the force of friction between the drive wheel and the road
Tread: This is the part of the tyre that comes into contact with the road.
Tread Depth: The measurement between the top of the tread runner to the tyres deepest grooves. The legal limit for tread depth is a minimum of 1.6mm
Tread Wear Indicator: These are narrow bands in the tread grooves which provide a visual warning when tyres need changing. These become visible if the tyre falls below the legal limit of 1.6mm
Tubeless: usually a radial tyre these are constructed with an inner liner to protect against loss of pressure during normal use
Tyre Compound: A “mix” or combination of raw materials used in the manufacture of the rubber compound of the tyre itself. By varying the percentage or the composition of the materials applied, manufacturers can produce different tyres for various purposes and with different performances.
Tyre information: Found in the vehicle handbook or sometimes of the inside sill of the driver’s door, this information outlines the recommended pressure, rim size and load capacity
Tyre Pressure Monitoring System (TPMS): This device, usually attached in the wheel wall, or to the tyre which can send information to a dashboard display whilst the vehicle is in use. If there is a loss in pressure the driver is alerted. Note: run flat tyres (link) can only be used if a vehicle is fitted with a TPMS
Tyre Pressure: This is the amount of air inside the tyre measured in PSI or in Bar The correct pressure can be found in the vehicle handbook and usually on the inside of the petrol tank flap. This should be changed regularly as tyre pressure reduces gradually over time. Note, tyres should never be inflated beyond the maximum pressure specified in the vehicle manufacturers handbook
Tyre Size: (width, profile, rim size, load rating and speed rating )
It is vital that your vehicle has the correct tyre size fitted. You can check what sizes of tyre are suitable for your vehicle in the manufacturer’s handbook but you must ensure that your vehicle currently has these tyres fitted. You can check your tyre size on your tyre sidewall.
Tyre Wall: The area on the tyre where information about the tyre is displayed
Under Inflation: A tyre with insufficient air pressure
Under Steer: When a car fails to respond to drivers steering and continues to drive straight. This is the opposite to oversteer
Valve: Allows the tyre to be inflated to the correct pressure. Valves are usually made of rubber, with a metal core assembly with a screw on dust cap. There are 2 standards lengths, short for most alloy wheels and long for steel wheels which have a plastic wheel trim
Winter Tyres (also see Cold Weather Tyres ): These Tyres which are constructed using special compounds designed for use in winter driving conditions including temperatures below 7 degrees Celsius. Can include multiple blades or Sipes for increased grip in slippery conditions