As mentioned in the product page, USB is just used for lighting. On the other hand, there is way more resistance that I can use when I increase the cadence, so the relatively low power limit (by direct-drive standards) of 1128 W / 60 km/hr is not an issue for me! Love love them. 2g. They give just the right lift to your legs and feet in a way that takes the strain off of your back. When you first turn it on, if youre in a quiet place you might be alarmed by all the static that comes out of the speaker though it seems to lessen to acceptable levels after a bit of time passes and/or you actually start using it. I ordered large so she could wear it again next year. It also feels very comfortable and is made of good quality and extremely durable. This buy here doesnt even tell if its Optional until youre package comes in with the box saying is optional. I needed some extra cargo space for our planned move across country this past month.