Lug nut

As the wheel bolts and nuts fasteners are screws and nuts, denoted by which the wheels or rims are mounted on the wheel carriers of multi-track motor vehicles and trailers. Wheel nuts are screwed onto the wheel carriers mounted in studs. Wheel bolts are screwed into an internal thread on the wheel carrier. When cars are now mainly wheel bolts, also called wheel studs, installed.

Forming the connecting elements

Hereinafter, the term is only used nuts, even if the corresponding statement applies for wheel screws as well.

Wheel nuts have a conical or spherical contact surface to the edge of the hole in the rim. The centering effect of the contact geometry is now secondary, since the rim is centered on its central hole in the wheel carrier of the control. On older vehicles, center the rim was reached on the wheel nuts. While this distinction is irrelevant for the tire change, it must be especially taken into account when balancing the wheel. With alloy wheels, a flat seat is in use.

For loosening or tightening the wheel nuts is usually a wheel wrench or a socket wrench in hex ​​form is used with the appropriate key length. Workshops mostly use impact wrenches, which are operated by compressed air.

For steel rims the environments of the mounting holes give way elastic. This creates a self-locking screws elastic compound similar to an expansion screw connection.

For the arrangement of the mounting points different diameter are used; the number of holes in the rim will be prepended to the label. Thus, there are names such as 4 × 98 (smallest common diameter: 98 mm ) and 6 × 139.7 (greatest common diameter ) for the bolt circle. On cars are four to five lug nuts per wheel in use. In Automobiles French manufacturer sometimes only three fasteners are installed. In buses, trucks and agricultural machinery far more lug nuts are common.

Wheel nuts can be designed vehicle-specific with different threads and key lengths. So you can find on vehicles from Japanese manufacturers, for example, often the size M12 × 1.5 ( thread diameter × pitch), wrench size 21 is decisive for the correct position of the mother is the shaping. A distinction is made between a conical (often 60 °) or spherical executed covenant. The federal government is the area with which the mother pressed into the corresponding well of the rim, so a wheel nut must always be designed to fit the rim respectively used to obtain a positive connection. It is not self-evident that the nuts fit on the same vehicle for the alloy wheels with summer tires on steel rims for winter tires. Under no circumstances should wrong or different nuts are used for fastening a wheel, because then there is a danger of them falling off accidentally.

Protection against theft

To complicate the theft example of high-quality aluminum wheels and tires, there are screw or nut sets (sets) with special heads, so-called wheel locks that can not be solved with a hexagon, but only with a special key. At each wheel is then sufficient one of these special shapes.

Tightening

Since the lug nuts holding the wheel on the wheel and thus the car, it is important that the wheel nuts are tightened to the correct torque. Therefore, it is recommended that further tightened each nut with the torque wrench after tightening the wheel nuts with the pneumatic screwdriver (or similar tool ). After every wheel check the tightening torque of the wheel nuts after a short driving distance (eg 50 km) should be checked again. Some workshops therefore left after removing a wheel, a note to remind you in the car. The exact torque value depends essentially on the nature of the thread, rim type and the materials used. In most cars, a torque of between 100 and 200 Newton meters (Nm) is specified in the technical documentation.

Protection against contact corrosion

When changing a wheel corroded wheel nuts often cause problems, so it may not be possible under certain circumstances during a flat tire on the road, the other to perform a tire change in the car with the included tool without help. For this purpose, then a wheel wrench or a tool with an extra long handle is required.

A few manufacturers, such as Porsche, allow special lubricants on the threads or bearing surfaces. Generally be considered in the absence of specific instructions from the fact that the thread and taper must not be lubricated. The tightening torques specified by the manufacturer are valid only for ungreased screws. The surfaces are therefore at best with a wire brush to rid of surface corrosion.

General-purpose grease is not suitable, to prevent rusting of nuts, as occur in the vicinity of the brake discs to high temperatures. More suitable copper paste, which contains lubricating grease also thermally stable particles.

Screw and central nut

For particularly fast wheel change (as they are for example in motorsports required), most racing cars and some sports cars like the Porsche 997 GT3 RS 3.8 3.8/GT3, mostly as a " central locking " designated central nut or central screw. By loosening or tightening this single nut or bolt can be a single wheel to remove or fix the car.

As a special central locking are mostly attracted towards the direction of the wheel. On the right side of the vehicle, the connecting elements have then left-hand thread.

Norms and Standards

• DIN 74361 - Disc wheels for motor vehicles and trailers