ANSWERS FROM ASSORUOTE
QUESTIONS ABOUT THE WORLD OF RIMS
THE WORLD of wheels is still little known to those outside the sector, but rims play an important role in road safety. They have a specific task that is not within the province of other components and are actively involved in vehicle performance.
More information and knowledge about this technological and complex product are a necessity and it is here that Assoruote, the Italian Association of Wheel Manufacturers, has a decisive role and invests considerably in raising the awareness of drivers, operators and institutions.
Its many actions include a guide to the world of wheels: twelve FAQ that have been prepared by Assoruote to explain some of the essential aspects of the product.
1. Is it possible to repair alloy rims that have been damaged?
No. When an alloy rim has been damaged by impact, the deformation of the material is permanent.
From this moment on, the mechanical characteristics and structural strength of the material cannot be restored by any type of repair (including welding).
In the majority of cases, the product’s mechanical characteristics deteriorate during repair operations and the strength of the rim is considerably reduced under load or on impact with potholes, etc.
The molecular disruption of the repaired section is not resolved.
Attention should also be paid to cosmetic repairs of rims. Where indicated by the manufacturer, the alloy must be protected with a special protective layer of paint that will prevent corrosion that can also negatively affect the mechanical characteristics of the material.
Another contraindication: repaired wheels cease to be covered by guarantees.
2. RUN FLAT and EH2+ tyres. What does this symbol mean?
RUN FLAT tyres are those with a self-supporting structure. In other words, they have reinforced shoulders that allow the vehicle to be driven for short distances and at lower speeds in the event of a simple puncture or total deflation.
EH2+ is the type of flange on alloy wheels.
In effect, there are no laws or regulations that make certain types of wheels compulsory for RUN FLAT tyres, only indications by the tyre manufacturer or, in some cases, the vehicle manufacturer; obviously, the latter is stricter because they take system functionality into consideration and not the single part we are talking about.
In fact, many tyre manufacturers recommend using EH2 or EH2+ flanges because they have humps that ensure that the tyre will not detach from the wheel.
Tyre and car manufacturers also maintain that the introduction of pressure sensors should be compulsory as they are very important for warning the driver that tyre pressure is no longer optimal.
3. What does the KBA number mean on rims?
The KBA number refers to wheel homologation. It is a document issued by the German Ministry for Transport for a certain group of one or more vehicles. This type of homologation is valid only for the German market.
4. Is rim homologation compulsory in Italy?
At the moment, no. But a technical regulation is currently being defined for rim homologation in Italy. When it comes into force it will be compulsory for all rims, with the exception of those mounted by the vehicle manufacturer.
5. Can rims have ECE homologation?
Certainly. But ECE homologation is only possible in certain cases and for certain types of rims. ECE homologation cannot be applied to all products on the market.
6. What type of safety tests do rims undergo?
A rim is normally considered safe when it has passed the following tests, which are now standard in most parts of the world.
• Rolling test. Pressure is applied to the rim and tyre unit to push it against a roller that simulates the road surface. The entire life of the rim is simulated in accordance with special cycles that vary depending on the testing standard and specification.
• Rolling flexion test. The rim (without the tyre) is subjected to a force that simulates vehicle load when cornering.
• Impact test. This simulates the impact on the rim and tyre unit when hitting a pavement or obstacle.
All these tests have a series of parameters that vary depending on the reference standard and test specification.
7. What are the advantages of winter FITTED UNITS?
The first advantage is in performance; it is possible to choose the most suitable rim size for winter tyres (normally it is narrower and smaller in diameter). Many car manufacturers now provide tyres in special sizes (smaller), thereby optimizing the choice of the most suitable rim for winter tyres, which also makes a set of 4 tyres more affordable.
The second advantage is a practical one in that the tyres do not have to be removed from the rims at every change of season. This optimizes time and cost and reduces the stress that tyres are subjected to in changeover operations.
8. Can rims extend beyond the outside edge of the vehicle?
There is a special European directive on this subject (74/549/CEE), but it is fairly detailed and the real limits of this specification are not easy to understand. As a rule, the rim and tyre unit should not extend beyond the edge of the vehicle wing.
Obviously, certain technical details must be taken into account, but in reality the upper part of the wheel (from wheel centre upwards) is normally within the outside edge of the vehicle wing.
9. There are load indexes for tyres; is there anything similar for rims?
Yes. The parameter for rims is usually called MAX LOAD.
The difference is that this value is not specifically indicated in or found with certainty in vehicle registration certificates in Italy (unlike the load index for tyres).
Normally, vehicle load is taken into consideration when manufacturing alloy rims, but obviously it is the responsibility of the installer to ensure that the vehicle load corresponds to the max load of the rim to mounted.
To do this, rim manufacturers prepare lists of dedicated applications with all these data.
10. What can be done to maintain rims properly?
Check that no part of the rim is corroded.
Avoid repairing or modifying rims and do not change the finish.
If the rim is damaged, replace it with a new one.
Always follow the manufacturer’s instructions.
11. Wheel markings: the unknowns.
Like all products, the marking and therefore the traceable nature of rims is the first thing that differentiates a serious manufacturer from a less reliable one.
Usually, wheel marking includes:
• Wheel manufacturer
• Wheel model
• Size and flange type
• Version/adaptation (ET, PCD, c.b.)
• Date of manufacture
• Made In
The wheel manufacturer should also mark the product with other important information such as the logo, homologation number, max load, etc.
12. Alloy and steel rims: the differences.
The differences concern aesthetics, weight and construction method.
On the one hand, aluminium, on the other, high tensile steel, casting processes for alloy wheels and rolling and welding operations for steel wheels, disc (flange) moulding and, lastly, assembly of the rim and flange and relevant welding.
Although they cost less, manufacturing steel rims requires complex systems and machinery, with numerous quality control points (geometric and functional) both on and off the production line. Weight optimization is requested by all manufacturers and research has led to the development of steel specifically for wheels, which means that they are thinner and product safety requirements are guaranteed primarily by highly automated and controlled production processes.