Rad Carsten answers your questions
The Aluminium Wheel FAQs
Whenever anyone has questions about light alloy wheels, I ‘m the man – after all, I really know my stuff. And to keep from having to answer each question umpteen times, here’s a bunch of questions that I get asked again and again – of course with the corresponding answers. So if you have a particular question, just scroll through the list of questions that I’ve already answered. And if you don’t find what you need, just click on the ? and write me an e-mail. I’ll be with you then shortly.
- Which Borbet rims can I use for run flat tyres?
- Does the offset affect the appearance of the vehicle?
- What do the abbreviations „mam, bcp etc.“ mean on the Borbet wheels?
- I don’t have an approval certificate for my car - what should I do?
- What torque should I use to tighten the wheel bolts/nuts?
- How many times do I have to turn the wheel bolt to make sure it sits tight?
- What is a KBA number?
- Which TPCS can be used for your wheels?
- What is the “rolling circumference”?
- I want a wide track so that the tyres stick out more - what do I have to do?
- What is a “pitch circle”?
- What does “undersizing” mean?
- What do the individual elements of a designation such as 195/65R 15 91 H mean?
- I found the word multiflex in a wheel designation - what does it stand for?
- What are COC documents?
- What does fixed bore mean?
1. Which Borbet rims can I use for run flat tyres? Currently only the CC 7 x 16 ET 34 is available from the BORBET wheel product line. These really smart aluminium wheels have the so-called EH2 system, that is, a different shaped rim which guarantees the properties needed for driving in an emergency, and therefore these rims are suitable for run flat tyres.
2. Does the offset affect the appearance of the vehicle? Of course. The higher the offset, the farther inside the wheel housing the wheel is, and the lower the offset, the farther outside the wheel housing the wheel is. But it’s also dependent on the rim size. Example: With the same offset, the outer edge of a 7.5" wheel is 1.27 cm farther outside than with a 6.5" wheel – of course it also comes 1.27 cm farther inside.
3. What do the abbreviations „mam, bcp etc.“ mean on the Borbet wheels? Those are the colour codes of the wheels. Here’s a list of the abbreviations and their meanings:
- ks= crystal-silver
- ksp= crystal-silver polished
- bs= brilliant-silver
- ds= decor-silver
- bcp= black-chrome polished
- bp= black polished
- mam = mistral-anthracite matt
- map =mistral-anthracite polished
4. I don’t have an approval certificate for my car - what should I do? Don’t panic. First of all you should check whether there’s a comparable technical component report of the same magnitude. If you don’t find one, you still don’t need to panic. Simply write a nice e-mail to BORBET and tell them you need the particular wheel strength. There is a catch, however – no matter whether you find a comparable technical component report or receive the wheel strength data from BORBET, you and your car still have to go through the single component acceptance process (§ 21) at TÜV. And on top of that, you’ll have to get your vehicle registration document changed. But you’ll manage.
5. What torque should I use to tighten the wheel bolts/nuts? The following always applies to the torque needed to tighten the wheel bolts: Never too tight and never too loose. How tight is tight and how loose is loose can be found in the respective part certificates and/or in the ABE attachments. There is no single correct NM value, since the torque always depends on the number of holes, the weight of the vehicle, and the maximum speed.
6. How many times do I have to turn the wheel bolt to make sure it sits tight? To make sure your car doesn’t turn into a tricycle while you’re underway, each of the bolts has to be turned at least 6.5 times, that is, the load-bearing pitch has to be reached. When the threads are fine, sometimes 7.5 turns are necessary.
7. What is a KBA number? A KBA number is issued by the Kraftfahrtbundesamt (Federal Motor Transport Authority) in Flensburg. This number can be found on all BORBET dealership wheels near the valve hole. The KBA number guarantees that it is a so-called “serially produced part.” This ensures that even years later, there won’t be a problem with the TÜV registration. The KBA number is also the foundation for the ABE – without the KBA number, you won’t be able to pass the TÜV single component acceptance test.
8. Which TPCS can be used for your wheels? I’ve drawn up a proper list for those as well!
9. What is the “rolling circumference”? The rolling circumference is simply the distance which the tyre covers in one revolution – that is, when it rolls over once completely. The rolling circumference may deviate no more than 3 - 4% from the rolling circumference of the standard tyres. If the deviation is greater than 4%, the tachometer will have to be adjusted and a new emissions test will have to be performed.
10. I want a wide track so that the tyres stick out more - what do I have to do? First of all, make sure that you have a TÜV report for the spacers. And remember that you can widen the track not only with spacers and adapter discs, but also with a lower or higher offset.
11. What is a “pitch circle”? I don’t need to explain that here. Look under pitch circle in the Technical Jargon ABC.
12. What does “undersizing” mean? Undersizing means that the tyres you use are smaller than all of the tyres listed in the vehicle registration document or in the COC documents. But remember this: Undersizing is definitely not recommended. Or in legally: It is prohibited by law to drive a vehicle with undersized tyres in Germany.
13. What do the individual elements of a designation such as 195/65R 15 91 H mean? The best explanation of all is in the Technical Jargon ABC.
14. I found the word multiflex in a wheel designation - what does it stand for? Multiflex is a centring system in which a centring ring is used to adapt the diameter of the hub and the hub hole to one another. This offers the advantage that the wheel can be fitted to various vehicles.
15. What are COC documents? The COC documents – COC stands for Certification of Conformity – contain all of the tyre and wheel sizes approved of by the manufacturer of the particular vehicle. Since October 2006, newly issued vehicle registration documents now usually contain only the wheel/tyre combination that was mounted on the vehicle at the time it was purchased. All other approved wheel/tyre combinations can be found in the COC documents.
16. What does fixed bore mean? Fixed bore wheels are adapted precisely to the standard hub size of a certain vehicle – no multiflex rings are needed for mounting.