Tyre lexicon

Tyre pressure plays a definitive role in the service life and safety performance of your tyres: under- or over-inflation reduces the tyre’s grip, causing excessive or uneven tread wear and damaging handling. If the inflation pressure is inadequate for the load being carried, the tyre temperature increases, which can result in structural damage to the tyre and even tyre failure. Because 50% of all passenger vehicles run on tyres with the wrong air pressure, the tyre’s life span is significantly reduced.* The positive effects of the proper tyre pressure in relation to the vehicle manufacturer’s recommendation are fuel economy, driving characteristics and the tyre’s life span. To find the correct tyre pressure for your vehicle, please refer to your vehicle owner’s manual, the fuel tank cover, the car door or glove compartment. It is recommended to check the tyre pressure every two weeks and adjust as necessary. Do not forget to check the spare or emergency/temporary spare tyre. Please also note the vehicle manufacturer’s supplementary information regarding emergency/temporary spare tyres.

Check the tyre pressure at least once a month and before longer journeys. Carry out this check when the tyres are cool (after the vehicle has been still for three hours and is then driven fewer than two kilometres). Adjust the tyre pressure to the vehicle manufacturer’s specified pressure as long as the tyres are cold. Never let air out or reduce the tyre pressure when the tyres are hot. Increased air pressure is normal when driving. Use a precise tyre pressure gauge to check the air pressure and keep the pressure at the level recommended by the vehicle manufacturer. Do not forget to also check your spare tyre. Spare tyres require a higher air pressure. Please note: air pressure that is too low is the most common cause of sudden loss of air or sudden tyre damage and can lead to unexpected loss of control over the vehicle as well as accidents.

* Tyre pressure in relation to the vehicle manufacturer’s recommendation.

The all-season tyre classification is a compromise between a tyre developed for use on dry and wet roads during summer and one developed for use in winter conditions. The type of rubber and the tread pattern best suited for use in summer conditions cannot, for technical reasons, give good performance on snow and ice. The all-season tyre is a compromise, and is neither an excellent summer tyre nor an excellent winter tyre. All-season tyres are also marked for mud and snow the same as winter tyres, but rarely with a snowflake. Owing to the compromise in terms of performance during summer, winter performance is usually poorer than a winter tyre.

The contact area of the tyre to the road is reduced when water is on the road. In extreme cases, the vehicle hydroplanes (glides) on the water, thus drastically reducing control of the vehicle. Tyres have special tread patterns that ensure optimum drainage of the water away from the tread surface. This effect does, however, reduce proportionally as speed increases. The most effective protection is to adjust driving speeds to the weather conditions.

An asymmetrical tyre refers to a tyre with a tread pattern that does not form in line symmetry or point symmetry to its central line; it thus has a distinctive inside and outside edge. Asymmetrical tyres may be mounted on either side of the vehicle. Since the tread pattern of many ordinary tyres do not form symmetry in relation to design or pattern noise, the method of mounting tyres is specially prescribed.

At high speeds, tyres generate enormous centrifugal forces. Even tiny irregularities of only a few grams in the tyre are multiplied by many orders of size. Such imbalance stresses tyres and suspension. This weight irregularity can be tested and identified at tyre dealerships and is balanced by adding small counterweights. Every time a tyre is fitted to a wheel, it should be balanced.

The bead of the tyre is that part which sits on the rim. At the centre of the bead is the core, which comprises a bundle of steel wires embedded in rubber. This provides a safe and solid seating of the tyre on the rim.

The distance required for braking depends on the speed of the vehicle, the condition of the road surface and the condition of the tyres – in particular, the tread. Check your tyre tread depth regularly and change your tyres when worn down to the tread wear indicators located at the bottom of the tread grooves.

The purpose of wheel camber is to reduce friction during cornering. The camber is measured when the wheels are standing on a flat surface. The difference from the vertical (inward or outward tilt of the tyre) is then referred to as either positive or negative camber.

Modern tyres are made of many different materials and components. Looked at schematically, there is the outer cover – the tread and sidewall – and the substructure, the casing. Casing components may include steel and/or textile cord plies, the inner liner (to make tubeless tyres airtight), sidewalls, the apexes, the bead core (keeps the tyre on the rim) and the bead reinforcement.

Even modern winter tyres can sometimes be of no help when there are huge amounts of snow and steep gradients. In these situations, traction, lateral control and reliable braking require tyre chains. In order to be prepared, it is recommended to try and fit chains in a so-called ‘dry run’. Snow chains must be draped over the drive wheels. Please also note that a maximum speed is given. With some low-profile tyres, the reduced space between the tyres and the wheel arch may leave no room to fit snow chains.

A tyre’s date of manufacture is indicated on the tyre sidewall at the end of the DOT serial number (see DOT serial number). Tyre manufacturers have adopted a standard identification system: four numbers that indicate the week and the year of manufacture. For example, the figures 0201 indicate that the tyre was made in the second week of the year 2001.

On standard tyres with symmetrical tread patterns, it does not matter which way the tyre is fitted on the rim and in which position it is fitted on the car. However, some tyre manufacturers have started producing tyres with specific directions of rotation in order to improve wet grip and optimise noise generation. The direction of rotation is marked on the side of the tyre with an arrow. This side of the tyre must be on the outside, and the tyre must roll forwards in the direction of the arrow for optimum tyre performance. A number of tyres with asymmetrical tread patterns are also now available which do not have a specific direction of rotation.

The DOT symbol certifies the tyre manufacturer’s compliance with the U.S. Department of Transportation tyre safety standards. The DOT serial number is located on the lower sidewall of the tyre, on one side only. Below is a description of the serial number. As of the year 2000, four numbers indicate the date of manufacture – the first two numbers identify the week and the last two numbers identify the year of manufacture. Prior to the year 2000, three numbers indicate the date of manufacture – the first two numbers identify the week and the last number identifies the year of manufacture. To identify tyres manufactured in the 1990s, a decade symbol (a triangle on its side) is located at the end of the DOT serial number. 

For example: DOT NJ HR 2AE2 529 529 = date of manufacturer, example: 529 (52nd week of 1999) or 5200 (52nd week of 2000). 2AE2 = tyre type code (coding for type of tyre optional by manufacturer). HR = tyre size code number. NJ = manufacturer’s plant identification code. DOT = reference symbol (certifies the tyre manufactures compliance with U.S. Department of Transportation tyre safety standards).

As of November 2012, a standard label for vehicle tyres became mandatory across Europe. The EU tyre label is based on three criteria and provides information on a tyre’s environmental and safety characteristics with the aim of increasing road safety and reducing fuel consumption.

The tyre label generally applies to tyres for cars, SUVs, vans and trucks. The tyre label only bears limited significance for winter tyres, as winter properties are not shown.

The tyre label does not apply to retreaded tyres or tyres that are not road-legal such as racing tyres, spare tyres and tyres for vintage or classic cars.
Tyre tests conducted by automotive magazines continue to be an important medium of information for the consumer, because they test up to 11 additional security-related product properties instead of the three criteria indicated on the label.

It is recommended that all four tyres be of the same size, construction and speed rating. If tyres of different speed ratings are mounted on a vehicle, the vehicle speed capability will be limited to the lowest speed-rated tyre on the vehicle. It is recommended that the lower speed-rated tyres be placed on the front axle. This should be done to prevent a potential over-steering condition. Vehicle handling may also be affected.

Mixed fitment:

When a vehicle has different tyre dimensions fitted to the front and rear axles, it is said to have mixed tyre fitments. Many powerful vehicle models now come factory equipped with mixed tyre fitments. In addition to the sporty aesthetics this configuration provides, mixing tyre sizes also increases driving safety. While rear-wheel drive benefits from the improved grip of a wide footprint, smaller front tyres help keep the car safely on track (the narrower the tyres, the easier the steering). However, a disadvantage of this configuration is that tyres cannot be rotated axle-wise during seasonal tyre changes (a practice that would be beneficial for even tread wear).

The footprint or tread surface is the part of the tyre that comes into direct contact with the road. It is pre-vulcanised and then applied to the carcass of the tyre by means of adhesive rubber. Braking and traction forces are transferred from the vehicle to the road through the footprint.
The tyre tread components (tread blocks, ribs and grooves) are located on the footprint, whereby the tread blocks are designated as the positive portion, and the tread grooves as the negative portion. Footprints differ greatly from each other depending on their intended use (off-road tyres, road tyres, racing slicks). There are also differences between summer and winter tyres. Under German legislation (Road Traffic Regulation or StVO), only tyres with tread on the footprint are permitted on public roads.

Grip refers to how much traction a tyre has on the road. The tyre surface ‘bites’ into the ground surface to ensure driving stability and braking performance. The material properties, tread structure and correct tyre air pressure are the most important factors for achieving the necessary grip. On the one hand, the rubber compound must be soft enough to adapt to the unevenness of the asphalt at a micro level; on the other hand, the structure of the tread blocks (wipers on summer tyres and sipes on winter tyres) must prevent the tyre from sliding in rain or snow. High speeds and wet conditions especially increase the risk of loss of grip. For this reason, the wet grip properties of a tyre is often the deciding factor when it comes to separating bestsellers from substandard products in summer tyre tests.

These symbols are found on the sidewall of the tyre indicating the load-carrying capacity of the tyre.

"Snow tyre" means a tyre whose tread pattern, tread compound or structure are primarily designed to achieve in snow conditions a performance better than that of a normal tyre with regard to its ability to initiate or maintain vehicle motion.

To optimise the mileage of your tyres, you should regularly check air pressure and tread depth, inspect tyres for damage, ensure correct mounting and observe the following: the tyres on the driving axle are subject to heavier wear than the free rolling tyres. For this reason, tyres should be rotated as recommended by the vehicle manufacturer in order to ensure even wear and minimise unnecessary vehicle maintenance costs. You should always have the balance of your tyres checked when you remount summer or winter tyres from storage, in order to ensure comfortable driving and prevent impact from vehicle chassis parts (see balancing).

No vehicle driver today should decide to mount their tyres on the rims themselves. Faulty mounting (e.g. using screwdrivers or similar tools) can damage the tyre bead or even cause the bead wire to break. Even if no external damage can be seen at first, driving safety is drastically impaired. In the worst-case scenario, a tyre may blow out leading to a total failure of the tyre. A tyre must also be balanced to ensure optimal driving performance. This process requires special technical equipment. 

Nitrogen is an inert (non-flammable) gas – basically, nothing more than dry air with oxygen removed. Ambient air contains about 78% nitrogen. Because of nitrogen’s inert properties, it is often used in highly specialised tyre service applications and/or demanding environments. These tyre service applications usually include aircraft, mining and commercial or heavy use. Nitrogen is also used in professional motor racing involving extreme vehicle speeds. Dry nitrogen is used in this regard to help reduce tyre pressure variations, where even small differences in pressure can affect vehicle handling at the extreme limits of performance. For service applications involving normal everyday consumer tyres, nitrogen tyre inflation is not required. However, nitrogen tyre inflation does not harm tyres and may marginally contribute to reductions in tyre inflation loss by permeation. Nevertheless, nitrogen will not prevent any tyre inflation loss caused by punctures, tyre/rim interface (bead) leaks, valve leaks, valve/rim interface leaks, wheel leaks and other mechanical leaks. The use of nitrogen alone does not substitute for the importance of regularly checking tyre inflation pressure. If the tyre inflation pressure is below the pressure specified on the vehicle placard, the tyre must be reinflated – whether with air or nitrogen – to the proper inflation pressure. Do not operate tyres when they are under-inflated and/or overloaded.

Off-road tyres are tyres that are especially designed for use on non-paved roads. They have a relatively knobbly tread in order to retain their grip on muddy and sandy terrain. All-terrain vehicles and SUVs (sport utility vehicles) are primarily fitted with heavily treaded tyres.

Overstressing of tyres (excessive speed or overloading) has the same
critical effect as under-inflation and can cause irreparable damage to the tyre.
Avoid overloading your vehicle. If you intend to drive under full-load/high-speed conditions, adjust your tyre pressure according to the vehicle manufacturer’s recommendations.

Radial tyres have body cords that run across the tyre nearly perpendicular to the beads. Radial tyres have belt plies, which are laid diagonally under the tread to stabilise and strengthen the tread area and add flexibility to the sidewall. By restricting tread movement during contact with the road, the belt plies increase tread life and traction and also improve handling.

Reinforced or XL (extra load) tyres are specially reinforced tyres. They can carry higher loads than a tyre of the same size. Reinforced tyres are designated on the sidewall by the letters “RF” and extra load tyres with the letters “XL”. Reinforced and XL tyres require higher inflation pressures compared to standard tyres.

The number of revolutions a tyre makes in one mile, at a given load, speed and inflation. Sometimes called revolutions per kilometre (RPK).

Rolling resistance refers to the drag force required to put a free rolling tyre into motion. Tyres are not rigid, but flexible. During driving, the tyres compress and flex – and this flexing absorbs energy, converting it into heat. In order to reduce rolling resistance, manufacturers use special rubber compounds. Any reduction in the rolling resistance of the tyre helps reduce fuel consumption. Since rolling resistance also increases with low inflation pressure, it is beneficial to check tyre pressure regularly.

Refer to your vehicle owner’s manual for the recommended rotation pattern and interval for your vehicle. It is recommended to rotate your tyres every 6,000 to 8,000 miles, or sooner if uneven tread wear begins to appear. The purpose of regular rotation is to achieve more uniform tread wear on all tyres on your vehicle. If tyres show uneven tread wear, ask the service person to check and/or correct any alignment or other mechanical problems before rotation. This is true for both front-wheel and rear-wheel drive vehicles. Full-size spare tyres should be included in the rotation pattern for your vehicle. Compact spares (temporary use spares) should not be included in the rotation pattern.

The tread blocks of a tyre have tiny slits called sipes. Sipes are able to open and close, optimising the traction and braking forces applied on the road (grip edge effect). Sipes are mainly important for winter tyres, guaranteeing better grip on snow slush, ice and wet road surfaces.

The Alpine symbol identifies winter tyres according to UNECE regulations (valid in the EU and various other countries) and the tyre regulations of the USA and Canada. The snow performance of these winter tyres has to be proven by objective tests and meet or exceed defined limits. These tyres provide high performance with regards to safety and control on snow, on icy roads and in general at low temperatures.

These are compounds that are particularly flexible at low temperatures and are suitable for journeys in Scandinavia, Russia and the Baltic states. The tyres safely transfer the driving forces even at low temperatures on snow-covered and icy surfaces. The proportion of natural rubber in soft compounds is considerably higher than in normal winter tyres. Thus, even under extreme conditions, they remain so flexible that they provide high traction similar to tyres with spikes. This approach overcomes the need for spikes so the tyres can also be used where spikes would be less helpful. This is mainly the case on roads that are free of snow and ice like those sometimes encountered on the coast of southern Norway.

Spare tyres are designed to carry the same load as the standard-size tyre on your vehicle and can be applied to any position. Maintain the proper inflation pressure as shown on the sidewall of the tyre; a spare tyre requires a higher inflation pressure than a standard-size tyre. Refer to the information on the sidewall of the tyre for proper usage. With such a tyre, a vehicle may be driven until it is convenient to repair or replace the disabled tyre. Have your standard tyre repaired or replaced as soon as possible, then return the temporary spare tyre to the trunk to conserve its usable tread life. The spare tyre can be worn down to the tread wear indicators just like your standard tyre. At such a time, the tyre must be replaced.

Speed ratings for tyres are identified by means of a speed symbol shown on the sidewall of a tyre. Although a tyre may be speed-rated, tyre manufacturers do not endorse the operation of any vehicle in an unsafe or unlawful manner. Furthermore, tyre speed ratings do not imply that a vehicle can be safely driven at the maximum speed for which the tyre is rated, particularly under adverse road and weather conditions or if the vehicle has unusual characteristics. Speed ratings are based on laboratory tests which relate to performance on the road, but are not applicable if tyres are under-inflated, overloaded, worn out, damaged or altered.

The use of tyre studs has been the subject of new regulations in Scandinavia since 2014. In order to classify tyres into three categories depending on their load index, multiple granite slabs must be driven across 400 times with studded tyres at 100 km/h. The slabs are weighed and the abrasive wear on the slabs is determined before and after each test drive. The tyres are approved if the test values fall within the prescribed thresholds. Legislators want to prevent studs from causing excessive wear to the roads. These tyres stand out visually because of their more solid tread design – and, above all, their studs. They provide maximum grip at extremely low temperatures and on icy and snow-covered roads. However, regulations concerning studs are very strict: studs must not protrude from the tread more than 1.2 mm, as they would otherwise break off, and their weight is restricted to 1.2 g. 

Summer tyres are specially designed for use in high temperatures. Their material composition achieves significantly better performance in terms of fuel consumption, wear and driving performance in warm temperatures than with winter tyres. Their tread is also optimised for driving in both dry and wet conditions. The ‘wiper effect’ they provide ensures short braking distances and high driving stability even on wet roads.

The service life of a tyre is a cumulative function of storage and service conditions that a tyre is subjected to throughout its life (e.g. load, speed, inflation pressure, road hazard injury, environmental influences, etc.). Since service conditions and tyre maintenance can vary widely, accurately predicting the service life of any specific tyre is not possible.

The influence of higher temperatures on tyre service life may be twofold:

1. Influence by peak temperatures usually maintained only for short periods of time. Such peak temperatures are typically reached in high speed applications. The tyre’s ability to withstand such heat and/or to dissipate such heat is checked and assessed by the tyre manufacturer and indicated by the tyre’s speed symbol as written on the tyre’s sidewall as part of its service description.
2. The influence of time/temperature exposure. The longer a tyre is exposed to higher temperatures, the more likely it will sustain detrimental changes in materials and properties. Further, the higher the temperatures, the more rapidly these changes will occur. Such changes may reduce the tyre’s robustness/resistance to fatigue, which may result in damage to the tyre. SEMPERIT recommends the following for tyre storage conditions: avoid storing tyres where they are subject to extreme temperatures. Do store tyres at temperatures not exceeding 35°C (95°F), preferable below 25°C (77°F). Tyre operating temperatures may be higher. However, the longer a tyre is exposed to higher temperatures, the shorter its useful service life.

SEMPERIT recommends removing from service all tyres manufactured more than ten years ago. If the tyre has been subjected to any significant time/temperature exposure, SEMPERIT also recommends that the tyre be removed from service earlier. If a customer is unsure as to whether a tyre should be removed from service or not, they should have it inspected by a trained tyre specialist without delay. As established by NHTSA (the National Highway Traffic Administration of the USA) and ASTM (Association for Standardization of Testing Methods), keeping a tyre at 65°C under certain defined harsh conditions for a duration of five weeks may represent a tyre’s aging in an extremely hot climate over four to six years. Another item to be considered is the influence of extremely cold temperatures. Very cold temperatures (below –30°C/–22°F for summer/high-performance tyres and below –50°C/–58°F for winter/all-season tyres) might lead to brittleness. Therefore, tyres in extremely cold temperatures should be carefully warmed up before use.

The toe describes the distance between the centrelines of the tyres on an axle. The toe setting can be adjusted on all cars. Since most wheels tend to run towards the outside because of the camber, most cars are set with a slightly positive toe-in. This means that the wheels are slightly closer together at the front than at the back. Incorrect settings for your vehicle result in uneven tyre wear. If you notice uneven tyre wear, then have your vehicle alignment settings checked.

The tread is that part of the tyre with the groove pattern that is in contact with the road. The tread is specifically designed to provide traction for stopping, starting, cornering and providing long-lasting wear.

The measured distance from the tread surface to the bottom of the main grooves away from the tread wear indicators. It is usually specified in millimetres.

Tread Wear Indicators are raised bars placed in the longitudinal grooves evenly around the tyre. If the tread pattern is worn out up to 3 mm for summer tyres and 4 mm for winter tyres, the Tread Wear Indicators become level with the tread pattern. Tread wear indicators are also placed at 1.6 mm, the legal minimum tread depth for both summer and winter tyres. We recommend changing to new tyres when your winter tyres reach a tread depth of 4 mm and your summer tyres a tread depth of 3 mm.

The service life of a tyre depends on the storage, rotation and service conditions. Since service conditions vary widely, predicting the service life of a tyre is not possible. Most tyre companies use a common coding system for checking when the tyre was made. This code is on the tyre’s sidewall. On tyres produced after 1999, the last four digits identify the date of manufacture: the first two digits stand for the week of manufacture, and the last two for the year. For example, a tyre marked 2214 was made in the 22nd week of 2014. All tyres (including spare tyres) manufactured more than ten years ago should be replaced, even if they appear to be usable from their external appearance and the tread may not have reached the minimum wear-out depth. The same applies to the spare tyre.

Tyres should be cleaned occasionally, and this is particularly important before mounting when switching between summer and winter tyres.
Do not use any cleaning agents containing solvents or oils, as they can damage the rubber! Ideally, use clean water with added soap or detergent.
When cleaning your vehicle with pressure washers, observe the following:
Never clean the tyres with a round-tip jet nozzle!
Keep a minimum distance of 20 cm when cleaning tyres with a flat-tip jet nozzle or a dirt cutter! 

A modern tyre is made up of:
Tread/belt assembly, comprising:
1) Tread – ensures high mileage, good road grip and water expulsion
2) Jointless cap plies – enable high speeds
3) Steel-cord belt plies – optimise directional stability and rolling resistance
Casing, comprising:
4 Textile cord ply – controls internal pressure and maintains tyre shape
5) Inner liner – makes tyre airtight
6) Side wall – protects from external damage
7) Bead reinforcement – promotes directional stability and precise steering response
8) Bead apex – promotes directional stability, steering performance and comfort level
9) Bead core – ensures firm seating on the rim

A tyre pressure gauge is a pressure gauge used to measure the pressure of tyres on a vehicle. Since tyres are rated for specific loads at certain pressure, it is important to keep the pressure of the tyre at the optimal amount. Tyres are rated for their optimal pressure when cold, meaning before the tyre has been driven on for the day and allowed to heat up, which ultimately changes the internal pressure of the tyre due to the expansion of gases.

Tyre code meanings:
1) 255/50 R20 V
255: Nominal section width in mm
50: Nominal aspect ratio (tyre height is 50% of tyre width)
R: Symbol for radial tyre
20: Rim diameter code (in inches)
109: Load index “109” = max. load of this tyre is 1030 kg
V: Speed symbol, indicating max. speed V = 240 km/h. Other information may be added after size marking: “REINFORCED” or “EXTRA LOAD (XL)” for reinforced tyres, “M+S” for winter tyres. The Alpine symbol identifies winter tyres according to UNECE regulations (valid in the EU and various other countries) and the tyre regulations of the USA and Canada.
2) Tubeless: Tubeless (TUBE TYPE tyres must be mounted with tubes).
3) M+S: "Snow tyre" means a tyre whose tread pattern, tread compound or structure are primarily designed to achieve in snow conditions a performance better than that of a normal tyre with regard to its ability to initiate or maintain vehicle motion. 
4) 224253: Approval number in accordance with relevant ECE regulation.
5) 1414: Production code (“14” means 14th week, “14” means 2014).
6) TWI: TWI = Tread Wear Indicator. Cross ribs evenly spaced around the circumference of the tyre in the main longitudinal tread grooves and which become level with the tread surface when the remaining tread depth is down to 1.6 mm.
7) E4: Marking in accordance with UN/ECE regulations. The number after the E in the circle indicates the country of homologation; E4 (4 = Netherlands).

The E4 symbol is on the other side of the tyre and thus not visible here.

Tyres can get damaged without the driver’s knowledge. If you discover or suspect damage, have the tyre inspected without delay by a tyre service professional. When driving over an obstacle, approach it slowly – as close to the perpendicular as possible. Check your tyres regularly for exterior damage such as cuts, cracks or bulges.

Tyres are removed from service for numerous reasons, including tread worn down to minimum depth, damage or abuse (punctures, cuts, impacts, cracks, bulges, under-inflation, overloading, etc.). Therefore, tyres must be inspected routinely. Consumers should be aware of their tyres’ visual condition and alert for any change in dynamic performance such as increased air loss, noise or vibration. Such changes could be an indicator that the tyres should be immediately removed from service.
It is recommended to fit the same type of tyres from the same manufacturer and with the same tread pattern on all four wheels as this makes for superior handling and braking performance in all driving conditions.

In Germany, the approved tyre sizes are specified in the vehicle registration under points 20 to 23. Additional tyre sizes and special recommendations (restrictions to certain tyre manufacturers and tread configurations) may also be noted under point 33. New vehicle documentation in Germany does not list all of the possible tyre sizes. Vehicles registered in Germany after 1 October 2005 are issued with a new type of documentation. The Zulassungsbescheinigung I (Registration Certificate I) is issued in place of the previous type of vehicle registration paper. The new vehicle documentation does not contain all of the information specified in the old registration. Details on tyres and rims are now omitted, among other information. The new Registration Certificate I will only specify a possible tyre size without information on rims in the future. Alternative wheel combinations are no longer included. Please note: the tyre size mounted on your vehicle is not always the same one entered in the registration document. Our specialist dealers can advise you on which tyre–rim combinations are possible for your vehicle.

In the case of a 185/65R14 tyre, the figures mean the following: 185 = width of tyre in millimetres; 65 = the ratio of the height to the width as a percentage; R = radial construction; 14 = diameter of the rim in inches.

Tyres should be stored in a dry, cool place, away from sunlight and sources of ozone, such as electric motors. If you must store tyres flat (one on top of the other), make sure you don't stack too many on top of each other. Too much weight can damage the bottom tyre. Also be sure to allow air to circulate around all sides of the tyres, including underneath, to prevent moisture damage. If storing tyres outdoors, protect them with an opaque waterproof covering and elevate them from the ground. Do not store tyres on or over black asphalt or other heat-absorbent or reflective surfaces, such as snow-covered ground or sand. Solvents, fuels, lubricants and chemicals should be kept out of contact with tyres. Spare tyre carriers on your vehicle are not intended to be used for long-term tyre storage. If your vehicle has a full-size spare (same size and type of tyre recommended for use by the vehicle manufacturer, not temporary use spares), it should be included in the tyre rotation pattern.

The valve, fitted in the wheel, ensures that the tyre can be filled with air. The correct valve is required for the correct wheel/tyre assembly; this is the job of the tyre dealer. The cause of a slow loss of air pressure can be a defective valve. The valve cap should always be fitted to the valve in order to protect the valve core from dirt and moisture.

The valve, fitted in the wheel, ensures that the tyre can be filled with air. The correct valve is required for the correct wheel/tyre assembly; this is the job of the tyre dealer. The cause of a slow loss of air pressure can be a defective valve. The valve cap should always be fitted to the valve in order to protect the valve core from dirt and moisture.

The tread grooves on a tyre surface form the negative portion of the tread. When the tyres roll over a wet surface, the water collects in the tread grooves and can be channelled away accordingly. Effective water displacement is hugely important for driving safety and prevents the occurrence of aquaplaning (or hydroplaning). Worn or bald tyre treads, in particular, increase the risk of aquaplaning significantly.

A wheel alignment adjustment may be necessary if the vehicle pulls to the right or the left when the steering wheel is in the straight-ahead position. Uneven tyre wear is another indicator of the need for an alignment check.

Winter tyres are specially developed for use in low temperatures and for driving in wintry conditions. Their tread blocks have a large number of sipes that ensure sufficient grip even on slick roads. The material compound is also carefully selected to keep the tyres elastic even in the cold. At high temperatures, however, winter tyres become too soft, which is why they should not be used during the summer.

Under German legislation (Road Traffic Regulation or StVZO), winter tyres must be marked with the M+S symbol. Individuals looking for additional safety with regard to the good driving and braking properties of winter tyres should only purchase models with the snowflake symbol. Germany does not stipulate a specific time at which winter tyres must be used. Instead, drivers have a duty to switch to winter tyres if driving conditions call for it. In wintry conditions (i.e. black ice, packed snow, snow slush or icy roads), only vehicles with M+S tyres are permitted on the roads. Individuals who do not drive in snow and ice can, in theory, continue using summer tyres even in wintertime. However, as summer tyres have material compounds specially developed for hot conditions, their use during the winter season is extremely dangerous and not recommended!