The importance of wheel rims

WHAT IS IT?

HOW DOES IT WORK?

IN PRACTICE

It is widely known that in motor racing, the tyres, along with the chassis and engine, are essential for good performance on both the qualifying lap and during the course of the race itself. In extreme cases, tyres are responsible for a driver or a team winning or losing. Indeed, it is no coincidence that nowadays throughout the various championships, including F.1 and MotoGP, everyone tends to use with the same tyres.
However, wheel rims also noticeably affect tyre performance, both on lap times and their overall duration. This is due to the materials the wheel rims are made of and their shape modifying the set-up of the kart and the temperature of the tyres.

You need to remember that excessively high temperatures cause abnormal tyre behaviour: when they exceed the ideal operating temperature, even slightly, this results in excessive grip, which slows the kart when it exits a bend, “gluing” it to the asphalt. Subsequently, the tyre temperature increases even more, which leads to excessive slippage. This is also due to the fact that an increase in air temperature inside the tyre causes an increase in pressure. This phenomenon expands the carcass and the deforms the tread, making it convex, which leads to a reduction of the footprint of the tread on the asphalt and a consequent decrease in grip.

WHEEL RIMS VARY IN TERMS OF MATERIAL AND INTERNAL SHAPE, WHILE THE OUTER DIAMETER IS REGULATED BY THE INTERNATIONAL FEDERATION ACCORDING TO CLASS

WHAT IS IT?

HOW DOES IT WORK?

IN PRACTICE

SOLID WHEEL RIMS

SPOKED WHEEL RIMS

A key variable of wheel rims is the material: they are essentially made of either aluminium alloy or magnesium alloy. The aluminium is less fragile: it deforms in case of collision, but is rarely breaks, while magnesium often fractures. The latter, however, is both more expensive and stiffer, weighing about 40% less, and has positive effects not only on the total weight of the kart, but also on the rolling inertia of the wheels and on acceleration.

WHAT IS IT?

HOW DOES IT WORK?

IN PRACTICE

Furthermore, thanks to a greater ability to dissipate heat, magnesium prevents the overheating of the air inside the tyre and keeps the temperature of the tyres themselves lower and more stable. In general, thanks to its greater stiffness, magnesium tends to release the kart and this, thanks to modern tyres, always aids performance.
It must be said that things change depending on the wheel rim model and the percentage of magnesium used in the alloy. However, the geometry is also important, as it affects the inner section and the support point between the wheel rim and the hub in particular. The first aspect determines the amount of air in the tyre and the speed with which it heats up and cools down (the more air there is, the longer it takes to heat up and cool down). The results are differences in set-up when driving down a straight, on which the tyres cool down and lose

grip, and in mixed sections, where the tyres heat up and recover grip.
The second parameter varies the stiffness of the rim-hub connection. In particular, the difference occurs between three-spoke geometries and the solid ones that are more common nowadays (on which the disc has a seamless flat surface that rests on the hub). The thickness of the wheel rim (typically about 8 mm) at the point it connects to the hub influences the stiffness of the connection.
Modern wheel rims also have security screws that prevent the tyres, which are becoming increasingly soft and therefore have high lateral acceleration values, from separating from the rim on bends. During the mounting and dismounting of tyres from the wheel rim, you have to remember to loosen these screws and then not to over-tighten them, to avoid damaging the rubber sealing ring and the thread in the seat of the wheel rim.

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Different internal shape

THE IMPORTANCE OF WHEEL RIMS