I have been asked by a number of members to explain the TUV wheel certification process in the plainest possible way. Here goes:

1.First, all the suppliers of a given product that is to be submitted for approval must have their quality system verified by TUV. No exceptions. This can either be an ISO 9000 certificate, TS/QS certificate like the OEMS use, or an actual TUV verification by an in-person TUV auditor.
In the case of wheels, this means the forging facility or foundry, heat treat facility, machining facility, etc. All must submit their documentation to the TUV prior to testing. The reason for this is obvious.
WARNING! Many companies receive this TUV Verification and try to convince the marketplace that their COMPANY is TUV "Certified". Not true. The TUV does NOT certify companies, only products, in this case wheels. However, you cannot submit wheels to be certified by the TUV unless your quality system is verified by the TUV.
2. Next, test wheels must be submitted in sufficient quantity for the test at hand. If you are getting wheels certified for just one vehicle, this is usually 3 to 6 pieces.
If your company is well known to the TUV, it is possible to get a "family" of wheels approved in a given style and diameter with a variety of bolt circles. This is complicated, but worth the effort.
3. Next, the TUV will test the wheels at whatever load that you state. This includes a variety of tests including radial fatigue, drop test, rotary bending, etc.
These tests are brutal and the test loads are up to 2 times higher than the stated load, just to be sure.
4. If the wheels pass, you will receive a "Gutachten" certificate from the TUV which states that the approved wheel is good up to a specific load rating. This certificate is "Wheel specific", not vehicle specific. At this point, the wheel would not be legal to sell for any vehicle. This certificate costs 3000 to 5000 Euros (sometimes more) because of all the testing involved.
5. If the wheel fails the first test, you have big problems. You will then have to submit twice as many wheels for the next test and the tests will be even more carefully scrutinized. Very expensive.
6. Once you have a "Gutachten", you can apply to the TUV for a "Teile Gutachten". This certificate will state that the wheel is approved for a specific vehicle. The TUV sets their own load requirements for each vehicle, based upon input from the original vehicle manufacturer. The teile gutachten certificate costs about 200 to 300 euros, because it is just a paperwork process.
To be very specific, a teile gutachten is a TUV approval for a specific vehicle or vehicles, and is not transferrable to another vehicle. For example, if the wheel manufacturer "weight optimizes" the wheel for a Porsche GT3, they cannot receive a teile gutachten for a heavier Turbo. Conversely, if the teile gutachten covers the Turbo, it will usually cover a lighter GT3.
You will receive a teile gutachten certification number and this number must be permanently inscribed on the wheel. The certificate in the car must match the number on the wheels. If you are stopped by the German police, everything must match or they will tow your vehicle.
7. If the manufacturer changes any vendors in the supply chain, new paperwork must be submitted to the TUV for approval. They will then decide if they want to re-test the wheels and issue new certificates.

This whole process is identical for every wheel manufacturer, large or small.
The vehicle OEMs are not required to do this because they certify the whole vehicle. (So technically, the OEM wheels are not TUV certified.)
So, if you are shopping for a wheel and the wheel manufacturer has a TUV teile gutachten for your vehicle, you can be reasonably confident that the wheels are safe for your vehicle. They could also supply you with test data from a testing company (Like STL) that states the wheels were tested at a specific TUV load. This is not a TUV certificate, but it does mean the manufacturer cares enough about safety to verify their engineering.

It is my professional opinion that more than half of all wheels sold in the USA are not subjected to third-party testing of any kind. So be careful.
The USA standards as set forth by the DOT are self-policing. You can probably imagine how well that works.

An example of an actual Teile Gutachten can be seen here:
http://217.160.41.106/gutachten/ch/c..._997-turbo.pdf
This one is from the BBS website but you get the idea.

Any wheel that is actually TUV certified will have such a document. NO EXCEPTIONS.

Companies that have been verified by the TUV will have a verification certificate. However, the TUV accepts other forms of quality system verification such as ISO 9000, QS, TS16949 and many others.