Chopper Frames

This will be a short post on frames and how their design is unique to choppers.

To understand what characteristics of a frame make a custom bike a chopper rather than a pro street or a bobber we need to know how custom motorcycle frames differ from stock frames. The definition of a “stock motorcycle frame” is not limited to only frames that come from the manufacturer. They would also include any frame that has the same backbone length, steering head height from the ground and rake as a factory bike.

A custom bobber will typically have the exact dimensions as a factory frame even if it is a rigid frame, meaning it doesn’t not have any rear suspension. A pro street frame on the other hand will generally have more rake in the steering head and may or may not have a longer backbone. As far as the steering head height it will either be the same as factory or little bit lower.

Now back to choppers. In my humble definition of what makes a frame a chopper frame is that it must have an increased steering head height. Even if the rake stays the same this will still give the illusion of increased rake simply because the height forces the fork tubes to be longer and thus pushes the front wheel away from the frame. You can not accomplish an increased steering head height without stretching the backbone of the frame and the downtubes of the frame.

To me, that downtube stretch is the crucial part that makes a frame a chopper frame. No stretch in the downtubes, no chopper. Everything else is optional. Of course it’s really not possible to stretch the downtube with stretching the backbone also, but how far you stretch the backbone is not limited to the amount needed to meet the stretched downtubes.

You have to go up and out, but you can chose to go more out then up or more up then out. When you see a frame is designated as 8″ up and 2″ out that means that the top of the steering head is 8 inches higher from the ground then it normally would be and two inches further forward then it normally would be. As you can imagine, then you really could have any combination you wanted, although obviously some will look or handle better than others.

OK, that’s my post on chopper frames. Please comment if you disagree with my assessment.