If you have a threaded bottom bracket, then it is simply a case of removing the old bottom bracket and replacing it with the new one that comes on the motor. You will however need to check that the spindle length is correct for your bike. As such, it’s important to look at your existing bottom bracket and check that the new one will fit. The good news is that most bikes made before 2012 using a BSA type square taper bottom bracket which these motors will fit. If however you have a later bike, especially if it is a more expensive one, please check the type of bottom bracket and then read on for advice.
If you have a press-fit bottom bracket, then the good news is that aftermarket conversion adaptors are available for bafang. As for CYC they offer different spindels for different types of press fit standards out of the box. These adaptors are quite universal so it’s likely that if you change bikes in the future, the motor will still fit.
It’s important to note that if you do have a press-fit bottom bracket, you will need to check the size. The most common sizes are BB92, BB89.5, BB86 and BB30. If you’re unsure of the size, then simply measure the internal width of the bottom bracket shell on your frame. This should be between 41-46mm for a BB92, between 37-42mm for a BB89.5, between 33-38mm for a BB86 and 30mm for a BB30. If you have a bike with an even larger bottom bracket shell (up to 50mm), then you can still use a Bafang, TongSheng or CYC motor, but you will need to get an adaptor made for your bike by a machine shop.