Cam lean is a condition in a compound bow where the top and bottom axles do not stay parallel with each other throughout the draw/shot cycle. Cam lean is usually associated with "side-load" or torque caused cable guards on bows. Cable guards are used to gain sighting and fletching clearance, but since the strings and cables cannot occupy the same plane, side loading occurs. The torque applied to a cable guard has increased with the introduction of shorter bows and larger, high performance cams. The larger a cam becomes, the further it displaces the string from the axle at full draw. Also, at full draw, much of the load is displaced to the cables, exacerbating the side torque applied by a cable guard. Cam lean was never a problem with the smaller round wheels of old, especially on the longer axle to axle bows of yesteryear. Today's bows are very susceptible to cam lean, as it causes greater tension/compression issues in the limb tips.
One of the ways to minimize the effects of cam lean is to adjust your cable guard for MINIMAL clearance. Next, twist the tension side of the split yoke to compensate for the compression on the other side. On single cam bows, however, it is impossible to eliminate the cam lean on the bottom cam since the power cable and take-up string both attach to the cable guard side of the bow. On a two cam, it is possible to minimize the effects of cam lean.
The only way to completely eliminate the effects of cam lean is to use a shoot-through design, which uses four cables instead of two, attached equidistant from the center of the primary string track, on either side.
Ideally, the axle assemblies on a compound bow should remain parallel throughout the entire shot cycle. But when a cable guard is used, there is always a measurable amount of change where the axles change their relationship to each other, causing excess string oscillation, bearing wear, serving wear and an increase in static friction.
