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Tyre Glossary

Air Pressure
Essentially - the amount of air inside the tyre. Measured in either pounds per square inch (psi) or bars. The correct pressure for tyres can usually be found in the vehicle handbook and often on the flap to your petrol tank.

Alignment essentially is the correct vertical alignment of a tyre. It is a process that ensures the suspension and wheels in association with the steering are in accordance with the manufacturers specification for the optimal way the wheels should be pointing.

Alloy Wheels
Alloy Wheels are different from Steel wheels because of their lighter weight, which improves the steering and the speed of the car. Ally Wheels conduct heat better than steal wheels improving the heat dissipation from the brakes and reducing the chance of brake failure in more demanding conditions.

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. The 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 panic.

Aspect Ratio (Also referred to as Profile)
This is a way of expressing a tyre's height as a percentage of its section width. This figure is always found on the sidewall of the tyre.

Tyre balancing is a process to ensure that the when the tyre and the wheel spin their weight is equally distributed.

Metric Unit for measuring Air Pressure (1 bar = 6.8947 psi).

A ring of steel wire, within a rubber ‘wrapper’, that helps to hold the tyre to the rim

The standard which all tyre repairs must comply with in the UK

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.

This is the skeleton of the tyre sitting underneath the tread and sidewalls.

Cold Inflation Pressure
This is the tyre pressure before the tyre has been able to heat up from driving.

Cold weather tyres (also referred to as Winter Tyres)
Tyre designed to give better grip below temperatures of 7 degrees. Also known as winter tyres but snow tyres are something different.

Footprint (also know as Contact Patch)
The area of the tyre's tread that is in actual contact with the ground. (See Contact Patch)

In a tubeless tyre, the innerliner prevents air from seeping out of the tyre.

Load Index
This is a code that ranges from 0 to 279 that quantifies the maximum weight a tyre can bear at the speed indicated by the speed symbol under certain service conditions.

Low profile tyres
A description of tyres that are quite ‘thin’ in comparison to the radius of the wheel.

Maximum Inflation Pressure
The maximum pressure that a tyre can be inflated to.

Mercedes Original Tyres

Pounds per square inch (psi)
The imperial unit for air pressure.

Profile (also referred to as Aspect Ratio)
This is a way of expressing a tyre's height as a percentage of its section width. This figure is always found on the sidewall of the tyre.

Rim Diameter
The diameter of the rim bead seats.

Rim Size
Distance between the two opposite inside edges of the rim flanges.

The metal edge of the wheel on which the bead is seated enabling the tyre to be supported.

Rolling Resistance
The energy needed to keep a tyre moving at a constant speed. A low rolling resistance means less energy is being used to keep a tyre moving.

Run flat tyres enable vehicles to be driven, at reduced speeds for a limited time until they can be replaced.

Section Height
Tyre height from rim to the outer tread.

Section Width
The measurement of the tyre from side to side excluding any additional sidewall items such as raised letters.

Found where the sidewall and tread meet.

The area between the bead and the start of the tread.

Sipes (also known as Blades)
Slits in the tread designed to improve grip in wet conditions.

Used to identify a specific tyre. It includes width, construction type, aspect ratio and rim size.

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.

Speed Rating
Speed rating to indicate the range of speeds at which a tyre can carry a load under a range of conditions. Ratings are categorised from A-Z.

A term used to describe the force of friction between the drive wheel and 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 Width
Tread width is the portion of the tyres width that is covered by a tread pattern. (measured in Millimetres)

The part of the tyre that comes into contact with the road

Tread Wear Indicator
Narrow bands in the tread grooves that provide a visual warning to a tyre needs changing, since they can only be seen if the tread has worn below the 1.6mm threshold.

Tyre Information
Information on the recommended pressure, rim size and load capacity can be found in your vehicle handbook and sometimes on the inside sill of the drivers door.

Made of a mixture of rubber, chemicals, fabric and metal their job is to give the car traction on the road in a variety of conditions, and to cushion the car from shock.

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 Pressure Monitoring System (TPMS)
This device, usually attached in the wheel wall or to the tyre, 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 can only be used if a vehicle is fitted with a TPMS.

Tyre Wall
The area on the tyre where information about the tyre is displayed.

Under Inflation
The condition that exists when there is not sufficient air pressure in a tyre.

Understeer (also caller oversteer)
This is a term used to describe a loss of grip to the rear wheels during cornering causing the car to slide sideways.

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 referred to as Cold Weather Tyres)
These tyre's are designed to give better grip below temperatures of 7 degrees. Designed from special compounds for increase grip in slippery conditions. NB: snow tyres are something different.

Terms and Conditions

*Prices based on 17” wheels. Models featuring tyre pressure monitoring system may cost more. Offer must be mentioned at time of booking/visit. Subject to availability. Cannot be used in conjunction with any other offer. Offer may be withdrawn or varied at any time. For full terms and conditions please contact your nearest Inchcape Mercedes-Benz retailer. Offer only available on Mercedes-Benz passenger cars and MO tyres.

Note: Whilst every effort has been made to ensure the accuracy of the information at the time of producing this, Inchcape Mercedes-Benz can take no responsibility for any errors in the content or consequences arising from such errors or misinterpretation of the content.

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