Frank:

As I understand it, the force-draw curve is a product of the radius of the string track compared to the radius of the cable track. In the case of the old style round wheels, the string track and the cable track were both round. The cable track loads the limb of course, so a round cable track only reached peak draw weight when the cable track radius from the axle reached its greatest point. The cam track was not at the greatest radius for more than that one point, so the force draw curve was below peak weight for most of the draw, and most people would describe the draw as smooth. When you look at energy wheels, they have a cam track that is not round, but oval, creating kind of a flat area. This " pumps up" the draw before and after the peak, increasing the stored energy.

The string track is also important. When the cam track curves in towards the axle, and the bow is approching letoff, the string track is often increasing in radius from the axle to increase letoff. The old High Country Phantom Extreme (hatchet) cams come to mind as I am thinking about that. Many older cams that stored a lot of energy were oval in shape, and then the hatchet style cam made it easier to get 65% of more letoff and still have the high energy storage, because the bigger string radius was letting more string out as the cable was loading the limb less.

The flat area at the valley of the cam track creates the wall that is felt at the back of the valley. Of course some designs have some kind of stop to make it even more solid. A sudden increase in the radius of the cable track would cause the draw force to increase dramatically and suddenly, creating a wall.

The actual size of the cam (string track) controls the amount of string that is actually let out. I am pretty sure that most of the parallel limb single cams have pretty big string tracks, as the limbs do not move backward significantly, but compress towards each other. Many of those, like the Mathews Straightlines also move their very stiff limbs only a small amount. The draw weight is kept at the same level as a bow whose limbs move more by letting more string out and moving the stiff limbs less.

Example: With Frankenstein, I could only get a 28" draw with the High Country hatchet cams, but with the physically larger Black Knight cams, it will draw 31" easily if I rotate the cams correctly. I can post more later, I have to go right now. Maybe you will hear from a real tech person.