OEM Parts
First, what are OEM parts? OEM stands for Original Equipment Manufacturer. This doesn't have to mean that the original manufacturer produced them. Many motorcycle manufacturers don't make every part used in their bikes. They have some parts designed and produced by outside companies and then install them on their motorcycles, or sell them as OEM parts. So, OEM parts are the same as the original part used in the building of your motorcycle. A couple other bits of information about OEM parts:
- OEM parts are usually more costly than aftermarket parts.
- Performance, look, and fit of OEM parts will be the same as the original part.
- Sometimes insurance agents will tell you that OEM parts have higher quality than aftermarket parts, and therefore are the best option for replacing parts.
One more important thing to consider is the length of your warranty or parts guarantee. If you violate your warranty, you can make it void. If your warranty is valid, use only accepted parts and have them installed by authorized mechanics.
Aftermarket Parts
Manufacturers of aftermarket motorcycle parts have to apply for the right to reproduce a part. These are parts you can order to alter, or personalize your bike. Aftermarket parts should perform as well or better than OEM parts. Also after a period of time, the original bike manufacturer allows the original producer of the part to sell the part in their own packaging, usually at a good discount—this is an aftermarket OEM part.
Again, you need to make sure you know what your warranty or guarantee period is. In some cases having an aftermarket part installed by an unauthorized mechanic will void your guarantee or warranty.
If you are looking to really up the performance of your bike you will probably find them as aftermarket parts.
The main point about motorcycle parts is that you should educate yourself as much as possible, and get the right parts for your bike.