The speed index, or V- or speed index, refers to the permitted maximum speed of the tire.

Also known as: Maximum tire speed

The speed index informs the driver about the maximum speed of the tire. In Switzerland, summer tires and winter tires must cover the maximum speed of the vehicle accordingly.

The load index, also known as LI or Load Index, is a coding and indicates the maximum permissible load for tires. The load index is noted on the tire sidewall. With the help of a table, the maximum permissible load per tire in kilograms can be determined. The load index table allows you to calculate the maximum load your tires can withstand. The load on your tire must be at least half the weight that can be carried by the axle. As a driver, you are probably aware that your vehicle is not designed for unlimited load. In the tire industry, a key figure has become established that can be easily calculated with the so-called load index. This provides information about the maximum load capacity. Why is observing the maximum load so important? It's about safety, because a tire can burst if the maximum load is not taken into account or if the specified upper limit for the load is exceeded or the load index is undercut with the chosen tires. This significantly increases the risk. This is not only about the maximum load (load index), but when driving at high speeds and heavy loads, forces develop during acceleration and braking that become a tough test for every tire. If the tire, due to its rubber compound, does not have the appropriate requirements for the load, it can also burst under the influence of pressure and force. This can lead to serious accidents.

The tire label, which became mandatory in the EU from November 1, 2012, is also present in the Swiss tire trade. It shows the values for rolling resistance, wet grip and rolling noise and thus provides important information about the energy efficiency, safety and noise emissions of a tire. Similar to energy labels for household appliances, it allows products to be compared and helps to find the best tires for individual needs. Around 20 percent of a vehicle's fuel consumption is due to tires. The main reason for this is rolling resistance. Lower rolling resistance reduces fuel consumption and CO2 emissions, thus contributing to greater energy efficiency in road traffic. Tires also play a major role in regular tire checks (air pressure). Those who do it right, for example by choosing low-rolling-resistance tires and driving with the correct tire pressure, can save a lot of money and energy. The tire manufacturers are responsible for the accuracy of the information. For you as a driver, the tire list is also important because, in addition to the ratings according to the tire label, it also contains a general quality classification. With the help of the tire label, tire buyers can find the best tires. These are energy-saving, safe, and quiet. Since August 1, 2014, the tire label has been mandatory in Switzerland.

Reduce speed

Aquaplaning describes the tire floating on the water film of a wet road. It occurs when the tire cannot displace the water on the road quickly enough. In this case, a wedge of water pushes under the tire's contact patch, leading to a loss of grip. At the moment of aquaplaning, no steering or braking forces can be transmitted to the road. The vehicle can swerve uncontrollably. Therefore, in rain or on wet roads, the speed should be adjusted. The risk of aquaplaning also increases if the tire only has 50% remaining tread depth (approx. 4 mm).

Overview of direct and indirect tire pressure monitoring systems.

Overview of direct and indirect tire pressure monitoring systems. Related topics: Direct system, Indirect system

Camper tires or Reinforced tires for increased load capacity

Also known as: Tires with increased load capacity

For reinforced tires, the understructure is particularly stable to achieve increased load capacity. A reinforced tire is a reinforced tire. This is mainly used for SUVs, vans, and off-road vehicles/SUVs. Reinforced tires are often marked with the additional designation XL. In technical jargon, this means "Extra Load" and indicates that this tire can carry more weight. Camper tires can carry even more weight. Camper tires are mainly found on delivery vans or transporters. For camper tires, the carcass and belt are particularly robust to meet the high demands. For camper tires, the ply rating is often additionally marked, which provides information about the layers in the structure (e.g. 4Ply/8Ply/10Ply/12Ply). An example: 195/70 R 15 99 C

Correct tire pressure is of decisive importance for a tire's mileage and lifespan, as well as for driving safety.

Also known as: Tire pressure requires regular checking

Warm and Cold Tire Pressure "Cold tire pressure" describes the tire pressure before the vehicle is driven. Tire pressure should be checked when cold. To ensure that the tires are cold, they should not have been driven for more than 2 kilometers. This ensures that the tire pressure does not expand due to warmth or heat. The air inside the tire heats up during driving. Temperature fluctuations are approximately between 20 and 100 degrees Celsius. Tire pressure specifications for passenger cars can be found on the B-pillar, in the owner's manual, or on the fuel filler flap.

Also known as: Run-flat tires - enables continued driving in case of tire damage

Tires with run-flat properties are entering the market, which, in the event of a tire puncture, allow continued driving at a reduced speed (80 km/h) for at least 80 up to 300 kilometers. The run-flat property is ensured by reinforced sidewalls that prevent the tire from flattening under pressure loss or blow-out and ensure adequate transmission of steering, braking, and driving forces. Since a driver hardly feels the difference between deflated and properly inflated tires, a tire pressure monitoring system is generally mandatory. These tires are called run-flat tires or run on flat tires. Depending on the manufacturer, they are marked with different abbreviations on the tire sidewall. With run-flat tires with run-flat properties, continued driving (at reduced speed) of up to 300 kilometers is permitted in the event of tire damage. Continued driving with run-flat tires is ensured by reinforced sidewalls. Since a driver hardly feels the difference between deflated and properly inflated tires, a tire pressure monitoring system is mandatory. These tires are called run-flat tires or run on flat tires. Depending on the manufacturer, they are marked with additional designations and different abbreviations on the tire sidewall.

The offset (ET) indicates how deep the rim's mounting surface is shifted from the center of the rim — crucial for track width.

Also known as: Offset, Wheel Offset

The ET number on the back of the rim is a signed millimetre value. ET +35 means: the mounting surface is 35 mm in front of the rim's center plane (outward direction). ET 0 = mounting surface exactly in the center. ET -10 = mounting surface 10 mm behind the center (typical for stretch look). A higher ET value (positive) pulls the rim further into the wheel arch, a lower one (negative) pushes it outwards. Changing from ET 45 to ET 35 means: the wheel protrudes 10 mm further outwards — it can collide with the fender. Registration in the vehicle registration document is mandatory from certain deviations. Important bolt pattern-ET combinations: 5x100/57.1 for VW, 5x112/66.5 for Audi/Mercedes, 5x120/72.6 for BMW.

Wheel spacers push the wheels further outwards by inserting plates — improving optics and track stability.

Also known as: Wheel spacers, Track widening discs

Wheel spacers are screwed between the wheel hub and the rim. They come in thicknesses from 3 to 30+ mm per side. Advantages: visually wider stance, wider track increases driving stability in fast corners. Disadvantages: higher wheel bearing load (lever arm increases), steering becomes more sluggish, tire can protrude from the wheel arch. Registration required in Switzerland. There are two designs: System A (continuous plate with its own studs, safe and reliable) and System B (simple spacer, uses the original bolts — not recommended for deviations over 10 mm per side). Mandatory: matching bolt pattern and center bore, otherwise the wheel will vibrate.

In Switzerland, there is no general snow chain requirement — it only applies when indicated by signs.

Also known as: Snow chain regulations, Chain obligation

Road Traffic Act Art. 29 stipulates that there is no blanket snow chain requirement on Swiss roads. However, if you encounter the round sign with the snow chain (mandatory sign 2.48), you must fit the chains to at least two drive wheels — without exception. Anyone caught without chains in a snow chain area risks fines and loss of insurance coverage in case of damage. Only chains certified for your tire size are suitable. Models with ÖNORM-V5117 or UNI-11313 test seals cover the Swiss standard. For all-wheel drive vehicles: chain all four wheels, otherwise the vehicle may react unevenly.

Wheel fastening in passenger cars is done via wheel bolts, wheel nuts, or threads.

Wheel fastening in passenger cars is done via wheel bolts, wheel nuts, or threads. Related topics: wheel bolt turns for fastening, wheel bolt torque, wheel bolt thread, wheel bolt shank length, wheel nuts, wheel nut thread, thread wheel fastening

The wheel balancing machine measures imbalances in grams and position — modern devices automatically detect the rim type and measure the tread.

Also known as: Tire balancing machine, Balancing machine

A standard balancing machine rotates the wheel at 250 rpm and measures vibrations with two sensors. From this, it calculates the position and weight of the necessary balancing weights — separately for inside and outside. Premium machines also measure radial run-out and lateral run-out — important for comfort at 130+ km/h. Sonographic sensors detect imbalances from 2 grams. When balancing, position the tire optimally on the rim: many machines suggest the optimal rotation angle so that less balancing mass is needed. Rule of thumb: Comfort class 2 grams, Sport 5 grams, Truck 25 grams tolerance.

With our tire and rim calculator, you can check in seconds whether a planned combination is within the tolerance range. You enter the tire width, aspect ratio, rim diameter, rim width, and offset (ET) — for both the original and the planned combination.

The calculator provides:

• Outer diameter, rolling circumference, sidewall height, and tire width with difference to the original combination.
• Speedometer deviation at 100 km/h according to UN-ECE R39.
• ET difference, rim width difference, track change per side, and total track widening per axle.
• A tolerance traffic light with clear indication of whether a rim expert opinion or an additional DTC expert opinion is required.

The visual top-down comparison immediately shows you how far the new wheel moves towards the fender or suspension — both wheels are precisely aligned at the mounting flange.

The tire marking on the sidewall follows a fixed scheme. Example 205/55 R16 91V:

• 205 — Tire width in millimeters, measured from sidewall to sidewall.
• 55 — Aspect ratio in percent: sidewall height as a proportion of the width (here 55% of 205 mm = 112.75 mm).
• R — Radial construction (standard today).
• 16 — Rim diameter in inches. 16″ = 406.4 mm.
• 91 — Load index.
• V — Speed rating.

From these values, the outer diameter can be calculated:

D = (Rim × 25.4) + 2 × (Width × Aspect Ratio %)
For 205/55 R16: D = 406.4 + 2 × 112.75 = 631.9 mm. From this, the rolling circumference U = D × π = 1985 mm.

The outer diameter is the total diameter of the wheel including the tire. For passenger cars, typical values are between 580 and 720 mm. Calculation: D = 2 × sidewall height + rim × 25.4.

The rolling circumference is the distance the tire travels per revolution: U = D × π.

Example calculation for 205/55 R16:

• Sidewall height = 205 × 0.55 = 112.75 mm
• Outer diameter = 2 × 112.75 + 16 × 25.4 = 631.9 mm
• Rolling circumference = 631.9 × π = 1985 mm

Since the speedometer calculates the speed from the wheel revolutions, a different tire size changes the speedometer reading. Rule of thumb: The rolling circumference should not deviate by more than ±1.5 % from the factory tire — up to ±3 % is generally registrable with a rim certificate.

The rim width is the distance between the rim flanges, measured in inches. It is the second important rim designation after the rim diameter. Common values: 6.5J, 7J, 7.5J, 8J, 8.5J. The suffix J denotes the shape of the rim flange.

For each rim width, ETRTO recommends a range of permissible tire widths:

• 6.5J → 175–215 mm
• 7.0J → 185–225 mm
• 7.5J → 195–235 mm
• 8.0J → 215–255 mm
• 8.5J → 225–265 mm

A rim that is too narrow for a wide tire deforms the contact patch and reduces stability. A rim that is too wide stretches the tire unacceptably (stretched tires) — which is safety-critical.

A CH rim certificate becomes mandatory in Switzerland as soon as the new rim/tire combination deviates significantly from the factory data. Specifically in the following cases:

• The offset (ET) of the new rim deviates by ±6 mm or more from the lowest manufacturer-permitted ET.
• The rim width or rim diameter is larger than the values registered in the vehicle registration document.
• The rolling circumference of the new tires is outside the ETRTO tolerance of approximately ±1.5%.

Process:

1. Submit vehicle and rim data (vehicle registration document, pictures with ET specification).
2. Review by our experts.
3. Issuance of the certificate as a PDF, typically within 24 hours.
4. Registration with the cantonal road traffic office together with the vehicle registration document.
5. Presentation with mounted rims.

For an ET deviation exceeding 15 mm, a DTC certificate is also required.

The DTC certificate supplements the rim certificate for significant deviations — especially for an offset difference of more than ±15 mm compared to the original rim.

While the rim certificate considers the rim and its direct compatibility with the vehicle, the DTC examines the effects of the increased track width on:

• Steering roll radius and steering behavior.
• Load on wheel bearings due to the extended lever arm.
• Fender clearance during compression and steering lock.
• Braking behavior and stability.

Both certificates are submitted together to the cantonal road traffic office. The tolerance traffic light in the tire and rim calculator shows you which documents your desired combination specifically requires.

UN-ECE Regulation No. 39 regulates two points for speedometers in passenger cars:

1. The speedometer must never show less than the actual speed.
2. The display may be a maximum of 10% + 4 km/h above the actual speed.

Example: At an actual speed of 100 km/h, the speedometer may show between 100 and 114 km/h — a value of 99 km/h would be impermissible.

A larger new tire combination leads to the speedometer showing too little:

actual speed = displayed speed × (C_new / C_original)

Changing from 205/55 R16 (U = 1985 mm) to 245/30 R20 (U = 2058 mm) results in an actual speed of 103.7 km/h at a speedometer reading of 100 — outside of R39. This can be checked in seconds using the tire calculator.

The ETRTO (European Tyre and Rim Technical Organisation) based in Brussels is the association of European tire and rim manufacturers. Its Standards Manual is the recognized reference for tire designations, compatibility between tire width and rim width, standard outer diameters, load capacity tables, and rim contours.

Particularly relevant for Swiss registrations are two points:

• Rolling circumference tolerance: Up to ±1.5% compared to the factory size is unproblematic, up to ±3% is generally registrable with a rim certificate, beyond that usually no longer.
• Rim width/tire width compatibility: For each rim width, ETRTO defines a range of permissible tire widths — it forms the basis of every serious rim approval.

Swiss road traffic authorities follow ETRTO standards when assessing tire/rim combinations — without ETRTO conformity, registration is generally not possible.