OE vs. OEM
OE (Original Equipment or Genuine BMW)
These are the parts that you get EXACTLY as if you are walking up to an authorized dealership and buying a part at the parts counter. (Example: Oxygen Sensor, BMW Part # 11 78 1 735 499). These parts usually come in BMW marked packaging.
OEM (Original Equipment Manufacturer)
OEM parts are parts that come from the same factory that makes your Original BMW parts, but they are boxed in their respective brands. BMW makes very few components themselves. Nearly the entire car consists of components and sub-assemblies sourced from various manufacturers or Tier-1 suppliers. (Example: Oxygen Sensor, Bosch Part #13231, which cross references to: BMW Part # 11 78 1 735 499). These parts are sold directly from the manufacturer to distributors, suppliers, or retailers and not through the BMW Dealer network. This usually means savings for the end consumer while still having the same OE standards that the vehicle manufacturer specified. They are identical - a lot of times you can find where the OEM part had the BMW logo ground off. In order to be labeled as an OEM part, it must meet the exact same design as the original part, regardless of where in the world it was manufactured. Any deviation from the original BMW spec is not considered OEM.
Some OEMs may choose to produce a performance version of the original design. Technically, these are no longer OEM parts but since they are coming from the original supplier you can be sure the quality is excellent and on par with the original. We generally refer to these as 'Performance Alternatives'.
Aftermarket parts are produced by manufacturers that have no connection with OE. These are generally copied from OE parts but produced and sold for less cost than an OE/OEM. They are not necessarily inferior, unsafe, or poorly made. But since they have not achieved OEM status their quality is not guaranteed. In some cases, we have found an aftermarket part to be superior than OEM but it is rare. Turner Motorsport will not sell a product with high return rates or one that receives too many customer complaints. Our experience is from twenty years in the BMW business with mail order, in-house servicing, and real racetrack experience influencing what we sell. In many cases we have learned to use only OE or OEM parts in many applications as the quality of the aftermarket part just doesn't live up to BMW or Turner standards.
"The bitterness of poor quality remains long after low pricing is forgotten," - Leon Cautillo, author.