Wheel Nut Redesign

The MART Formula Student MA23RT incorporates a wheel mount system with a central nut hub. Previous team vehicles featured a simpler system commonly used in road cars, which relied on four pressure studs for attachment. This change was prompted by the switch of rims from one season to another, so a new system was necessary.

However, the current design of the nuts has some problems, as a result of being the first model iteration, which need to be improved. Therefore, the following design modifications are proposed:

• Reorientation and redistribution of the holes for the locking pin.
• Incorporation of a non-threaded centering section before the thread.
• Increase in the contact area with the tool without sacrificing the overall volume of the piece.

Design

The nut and the hub are equipped with holes to fit a locking pin that acts as a safety system to prevent the nut from loosening under the loads that the wheel is subjected to when the vehicle is in motion. However, in the previous model it was difficult to match the holes to the desired tightening torque, due to the high rotational travel for low applied torque deviations.

A new distribution of the holes, as well as the number of holes and the offset between them, allows a total synchronisation between the hub and rim holes. This means that regardless of the position of the nut in relation to the hub, once it has been tightened to the required torque, the locking pin can always be fitted.

The new design adds an unthreaded cylindrical section at the thread entry. Thus, when the nut is brought close to the shaft, the nut is centred before it is threaded. This avoids damaging the first threads by misalignment between cylinders when bringing the nut close to the wheel hub.

The height of the hexagonal extrusion has been increased. This increases the contact area between nut and tool. This distributes the load more evenly when the nut is tightened.

Finally, roundings and chamfers have been incorporated into the design to improve the surface finish of the product.

Manufacturing

Six parts were sent for production, three with right-hand thread and three with left-hand thread. They were manufactured by CNC turning and milling processes and then treated with type III hard anodising.

Specs

• Material: Aluminium alloy 7075-T6.
• Weight: 71 g.
• Treatment: Anodized MIL-A 8625 Type III.