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Tyre Glossary - Tyre Terminology Made Easy

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Alignment of Wheels: This term generally describes the position of the wheels relative to each other and to the vehicle. The checks require specialist tools to ensure that the wheels are correctly aligned ensuring compliance with the manufacturers recommendations. In layman’s terms a wheel alignment consists of adjusting the angles of the wheels so that they are perpendicular to the ground and parallel to each other. The purpose of these adjustments ensures maximum tyre life, better fuel economy and a vehicle that does not pull to the left or right when on a straight even surface.

Wheel Alignment can be confused with Balancing. The two are separate. If a wheel is out of balance it may cause vibration at speed that a driver can feel on the steering wheel. If the wheel alignment is not correct, it can cause excessive tyre wear and steering or tracking problems.

All Season Tyres: These are Tyres that have been designed for use in all weathers all year round, they offer improvements in winter but they will not perform as well as winter tyres.

Aquaplaning: All vehicles in wet weather ride on a thin layer of water on the road surface and not the road itself. This in certain situations cause traction loss and potentially loss of control of the vehicle. The Vehicle you are driving can often feel “loose” at the back or front of the vehicle and may lose traction with the road completely. This is commonly known as aquaplaning. There are several skidpans around the UK where you can be trained by qualified instructors on what to do in this situation.

Aspect Ratio: - Profile This measures the Tyres Height/Tyres Width so in the case of a 215/55/17 Tyre would have a height of 118.25 giving an aspect ratio of 55%.

Asymmetric: When tyre tread pattern vary they must be fitted with the outside sidewall front edge of the wheel.

Balancing: Using specialist equipment wheels are balanced utilising either lead hammer on weights or zinc stick on weights for alloys. This ensures that the wheel is perfectly balanced at all speeds without vibration.

Bar: Unit for measuring Air Pressure (1 bar = 14.50 psi).

Bead: The bead is a fundamental part in tyre construction; it is typically reinforced with steel wires and forms the area that contacts with the rim. The bead seats very tightly on the rims of the wheel for 2 reasons:

• To allow a tubeless tyre to hold air with leaking
• To ensure the tyre does not shift circumferentially when the vehicle is moving.

Blades: - Sipes Are slits in the tread designed to increase grip by moving water away from tyres therefore improving grip.

Budget Tyres: - Economy Tyres At Event Tyres we sell a full range of tyres from Budget/Economy through Mid Range Tyres up to Premium Tyres brands. Each one serves a particular market for example you would not think of putting a budget tyre on a Porsche 911 Turbo, as it would require a premium tyre.

Carcass: This consists of the Ply, Bead area and belts; it forms the tyres structure that sits below the tread and sidewalls.

Camber:  This is determined and documented by the Vehicle Manufacturer and is determined by the suspension and hub construction which after a number of miles can show signs of wear which can affect the camber as can collision with kerbs. If the camber is out it can cause excessive tyre wear.

Centre-less Alloys: Citroen and Peugeot designed these wheels with no centre in them, which means a special adapter will need to be used, not all tyre fitting depots will have this adapter, all our event tyres vehicles carry this adapter.

Cold Weather Tyres / Winter Tyres : When temperatures fall below 7°C the rubber on tyres becomes harder which can mean difficult handling may occur, these tyres work well in temperatures below 7 degrees hence the name. For more information see our detailed explanation on winter tyres.

Contact Patch: - Footprint Tyre area in contact with the road. This varies depending on tyre construction, the compounds, tread design, and tyre pressure.

Footprint: - also see Contact Patch: The area of tyre tread that is in contact with the road surface

Load Index: This can be found on the tyre wall and is a guide indicating the maximum weight a tyre can carry at speeds specified in the speed rating of the tyre.

Low Profile Tyres: These are tyres with shallow sidewalls usually fitted to high performance vehicles.

Maximum Inflation Pressure: This can again be found in the handbook or on the sticker on the vehicle, this is the maximum tyre pressure to which the tyre can be inflated.

Mid Range Tyres: This range is a step up from Budget Tyres in terms of performance and price, yet it cannot be compared with Premium Tyres for performance. More expensive than budget tyres, less expensive than premium tyres.

Original Equipment (OEM): This is the tyre that was fitted to the vehicle in the factory it should be noted that there might be more than one OEM tyre supplier this though will be detailed in the handbook.

Over Steer: - Under Steer: When a vehicle through either excessive use of throttle whilst turning or entering a corner to quickly causes the rear wheels to lose grip sending the vehicle side ways.

Ply: Tyres have reinforcing elements as part of the construction process, which consists of fabric cord, and rubber, which provides strength to maintain tyre pressure whilst under load and resisting deflection.

Profile: - Aspect Ratio This measures the Tyres Height/Tyres Width so in the case of a 195/65/16 Tyre would have a height of 126.75 giving an aspect ratio of 65%.

PSI: This is the air pressure in the tyre measurement in pounds per square inch.

Radial Tyre: There are two different types of tyre construction cross ply and radial. A radial tyre can be indentified by the plies created in the process to form the carcass being radially oriented. Running across the tyre side to side at 90° to the road surface whereas cross-ply tyres plies intersect forming approximately a 45° angle to the road surface.  So what is the difference on the road, radial tyres have a very flexible sidewall but a stiffer tread area with cross-ply tyres having much stiffer sidewalls and a flexible tread area. The radial tyre is now used on all modern cars because it offers several benefits over cross ply:

• Because of the stable crown and larger footprint the traction is far superior
• The tyre does not have to work as hard due to less tyre slip, which leads to:
• Far longer tyre life with reduced wear of the tread
• Far superior fuel consumption
• Much improved handling and comfort whilst driving

Repairable Area: Many modern tyres when punctured can be repaired by an approved tyre repairer that works to the regulations detailed in the British Standard BSAU 159

Reinforced Tyres: Tyre manufacturers work in conjunction with vehicle manufacturers to ensure they construct the right tyre for every vehicle produced. In some cases where vehicles are produced with a greater weight than normal there is a requirement for a reinforced tyre to ensure safety when carrying heavier loaded vehicles.

Rim: There are 2 rims on each wheel and this is where the bead seats when the tyre is inflated

Rim Size: Normally measured in inches the rim size is the outside diameter of the wheel for example 245/50/18 – 245 is the tyre width in mm, 50 is the tyre profile in % and 18 is the rim diameter in inches

Rim Width: Each rim has two flanges, which prevent the tyre coming off the rim; the rim width is the distance between the two flanges.

Run-Flat: A relatively new innovation in tyres they are built with extremely stiff sidewalls that support the vehicle if the tyre loses all its air pressure. They help to prevent accidents as when a blowout occurs on a traditional tyre it is very easy to lose control of the vehicle especially at high speeds. They can only be used on vehicles where a tyre pressure monitoring system (TPMS) is used, as the driver would have no indication that the tyre had deflated. When deflated they should only be used for a short distance.

Shoulder: The sidewall and tread meet at the shoulder this is clearly visible on tyres take a look next time you are near your car.

Sidewall: The sidewall is the part of the tyre that is clearly visible as the name suggests it is the side of the tyre

Sipes: Are slits in the tread designed to increase grip by moving water away from tyres therefore improving grip.

Snow Tyres: This type of tyre has a specific function and is only used where snow is present on a regular basis they should not be used for normal road conditions

Space Saver Tyre: Now used by many manufacturers and essentially it is a get you home tyre. Significantly smaller than the tyres fitted to the car and they should be changed back as soon as possible. The performance of the tyre is poor compared to the original and speeds must be reduced when using the space saver tyre.

Speed Rating: An industry wide index that identifies the maximum speed at which the tyre can operate

Specified Load: This is similar to speed index again an industry wide index that specifies maximum weight to be carried on the tyre

Tread: This is the part of the tyre that keeps you going in the right direction it has many patterns that vary between manufacturers. You should regularly check to see if you still have a tread pattern for 2 reasons one safety and the other to avoid points and penalty fines

Tread Depth: This is easily visible and with a minimum tread depth of 1.6mm it should be checked regularly, you don’t though need to take a depth gauge with you as all modern tyres have wear indicators built into the tread pattern

Tyre Pressure: This is the pressure of the air inside the tyre, it can be measured in pounds per square inch PSI or Bar. Correct pressure for tyres is designed to aid fuel economy as well as safety as under or over inflated tyres can affect the handling of your vehicle. The manufacturer recommended pressures can be found in the handbook under tyre pressure and dependant on manufacturer the tyre pressure is usually detailed on a sticker on the vehicle.

Tyre Pressure Monitoring System (TPMS): This device is placed inside the rim and can be part of the valve, attached to the wheel or tyre. The systems are calibrated to detect a tyre pressure outside the parameters set by the manufacturer and they send a wireless signal to the dashboard of the vehicle warning of low pressure or deflation

Under Inflation: An under inflated tyre is not only dangerous it also increases fuel consumption and can damage the tyre beyond repair. Regular checks should be made to ensure your tyres are inflated to the right pressure.

Under Steer: Go into a corner to fast in slippery condition so when you turn into the corner the vehicle continues to go straight this is under steer. The tyre has lost its adhesion to the surface so the mass and speed of the vehicle prevents it turning under steer is the opposite of over steer.

Valve: The valve should have a cap on it and it is the short round metal or rubber item attached to the wheel. You attach an airline to the valve to increase or decrease you vehicles tyre pressure.

Winter Tyres/Cold Weather Tyres: When temperatures fall below 7 degrees the rubber on tyres becomes harder which can mean difficult handling may occur, these tyres work well in temperatures below 7 degrees hence the name. For more information see our detailed explanation on winter tyres