The biker jacket
The biker is the most recognisable leather jacket there is: an asymmetric front zip, a wide notched lapel that lies flat whether the jacket is open or closed, a belted or half-belted waist, and hardware that was designed to be seen. It was built for riding and it has never needed to be anything else.
Asymmetric or double rider
An asymmetric biker zips off-centre so the front overlaps and the wind stays out; it is the classic and it is what most people mean by the word. A double rider takes the same idea further, with a second layer of leather across the chest and more hardware. Both are cut close and structured; the double rider is the heavier of the two.
Full-grain cowhide, and what that means for the first month
These are cut in full-grain cowhide, which is stiff when new and softens with wear into the shape of the person wearing it. Expect the first few weeks to feel structured. That is the leather doing what it should; a biker that is soft on day one is a biker that will not last.
Fit
A biker should sit close at the shoulders and chest and end at the belt, not below it. It is worn over a t-shirt or a fine knit, not a jumper. If the size guide puts you between two sizes, take the smaller: the leather gives, the pattern does not lengthen.