What is compound bow let-off?
So you’re standing in an archery shop and you overhear an archer claiming his compound bow features 80-percent let-off.
And you’re thinking, “What the heck does that mean? What’s let-off?”
To begin to answer this question, you first need to understand how compound bows differ from recurves and longbows in the way they function.
Those other bows have a single string, and they draw all of their power from the limbs flexing. As a result, the string gets harder and harder to pull the farther you draw it back.
Compound bows also have limbs, but they’re much shorter than a recurve’s or longbow’s. They also employ cables and wheels, called cams, in generating stored energy that is eventually used to hurl an arrow.
By using cams and cables which aid in the drawing process, a compound bow is able to drastically reduce its draw weight about one half to two-thirds of the way through the draw cycle.
When the cams roll over, the draw weight drops, so an archer is holding considerably less weight at full draw than the peak draw weight.
The amount of weight reduction is used to calculate the bow’s let-off.
That is, a bow with a peak draw weight of 70 pounds, that has a full-draw holding weight of 14 pounds, is a bow with 80-percent let-off. Fourteen pounds is 20 percent of the peak draw weight, which means 80 percent of the bow’s peak draw weight has been shed or let off.
Compound bows primarily used for hunting commonly have let-offs of 75, 80 or 85 percent. PSE in 2017 introduced its Evolution Cam, which boasts 90-percent let-off.
In the hunting world, the benefits of high let-off are clear. Heavier draw weights are favored for their ability to drive arrows through game animals. But an archer might have to draw a bow early to avoid being seen by a game animal, and then hold the bowstring at full draw for an extended period while waiting for that animal to present the perfect shot.
Holding just 20 percent of a bow’s peak draw weight at full draw while waiting for that shot makes the task much easier.
Competition archers, on the other hand, don’t always like a huge amount of let-off. They feel they can hold a bow steadier with more weight at full draw, and so target compounds often have let-offs of 60, 65 or 70 percent.
Using a bow with 60-percent let-off, that archer pulling a maximum weight of 70 pounds would hold 28 pounds at full draw.
Remember, a recurve archer with a 28-inch draw length, shooting a 70-pound bow, would hold all 70 pounds at full draw.