How tire fitment works

Where approved sizes come from

Every new vehicle type-approved in the EU has a Certificate of Conformity. Entry 35 of that document lists the tyre/wheel combinations approved for the vehicle: the size designation, load-capacity index, speed category symbol, rim sizes and wheel offsets.

For drivers, the same information is repeated on the sticker in the driver’s door jamb, in the owner’s manual and sometimes inside the fuel filler flap. The vehicle manufacturer is also required to state which replacement tires have an appropriate load capacity and speed category.

The two minimums set by UN Regulation No 142

UN R142 governs how tires are installed on vehicles and applies to all vehicle categories in the EU through Regulation (EU) 2019/2144.

LoadFor tires fitted singly, the maximum load rating of each tire must be at least half of the technically permissible maximum axle mass of the most heavily loaded axle. The rule is per axle, not vehicle weight divided by four.

SpeedFor passenger car (C1) tires, the speed category symbol must be compatible with the maximum design speed of the vehicle. For V, W and Y tires the load rating at speed must also be taken into account.

Two further rules: all tires normally fitted to the vehicle must have the same structure, and all tires on one axle must be of the same type.

The winter-tire exception

A vehicle normally equipped with normal tires may occasionally be fitted with snow tires carrying the Alpine symbol whose speed symbol is lower than the vehicle’s design speed. The tire’s speed rating must then be either above the design speed or at least 160 km/h, and if the design speed is higher, a maximum-speed warning label must be displayed inside the vehicle where the driver can see it.

Tires marked only M+S, without the Alpine symbol, get no such exception under UN R142. Germany writes the same rule into StVZO § 36 (5): the lower speed must be shown by a sticker or an in-car display in the driver’s field of view, and must not be exceeded.

Alternative sizes

Using a size other than the approved combinations is permitted only where it is technically compatible and officially approved. Some countries allow exemptions if the overall diameter stays within about minus 2 percent and plus 1.5 percent; because the speedometer depends on tire diameter, a different size changes the displayed speed. That tolerance is a national matter, not an EU-wide rule.

In Germany, a change that could endanger road users voids the operating permit, unless the part carries an approval such as an ABE, an EC type-approval or a UNECE approval and any restrictions or installation instructions are followed. The approval document must be carried and shown on request unless the combination is entered in the registration certificate. Component reports (Teilegutachten) issued under the old rules may be used for installations only until 19 June 2028.

What RideVector will check

1. The original sizes listed for the vehicle, with load index and speed symbol.
2. Approved alternatives, each with its source and retrieval date.
3. Whether a candidate tire meets the minimum load index and speed symbol before any offer is shown.

Product concept. Fitment data shown anywhere on RideVector today is an illustration. Verified fitment sources are being prepared.