At first glance, mounting wheels on a vehicle seems simple – yet in practice, problems can arise. In particular, the risks posed by wheel bolts that are too loose or too tight are often underestimated. To avoid damage and safety risks, it is worth taking a closer look at the correct procedure.
What is preload force?
In order for the wheel, brake disc and hub to function as a single unit while driving, the wheel bolt must generate what is known as preload force. This force acts axially when the bolt is tightened and ensures that all components are firmly connected to each other – even under dynamic loads such as vibrations.
The torque applied generates a tensile force in the thread, which elastically stretches the bolt and slightly compresses the rim. Factors such as the tightening torque, friction in the thread, material properties, and the dimensions and strength class of the bolt have a significant influence on the resulting preload force.
Insufficient preload force – an underestimated danger
If the wheel bolt is tightened with too low a torque, the necessary preload force is missing. The result: components begin to vibrate, the connection loosens – in the worst case, the wheel can come off.
Even with multiple installations or rusty, dirty or damaged screw connections, the preload force decreases significantly as the friction value increases sharply.
Excessive preload force – risky overload
Anyone who tightens wheel bolts without a torque wrench runs the risk of tightening them too much. This can lead to unwanted elongation of the bolt and deformation of the rim – which is particularly critical in the case of aluminium rims.
If the wheel fastening is additionally lubricated, the friction decreases significantly. Even with a torque wrench, excessive preload force can occur, which in extreme cases can lead to the bolt breaking off.
Installation instructions for maximum safety
- Always observe the tightening torques specified by the vehicle manufacturer
- For precise power transmission: use only torque wrenches
- Replace bolts if they are rusted, deformed or have damaged threads
- Check the wheel hub thread for corrosion and dirt and replace if damaged
- Thoroughly clean corroded wheel mounting surfaces
- The contact surfaces of the bolt and rim must be clean, free of grease and undamaged
- Follow the manufacturer’s specifications: tighten the wheel bolts evenly and in the correct order
- Do not use impact wrenches
- Do not use oil or grease during assembly