What Is Let-Off?
The percentage by which a compound's cams reduce the holding force at full draw compared with its peak draw weight.
Let-Off: definition
Also called: let off, letoff, holding weight, cam let-off
Let-off is a feature of cam systems. As a compound is drawn, the cams roll over and the force on the string rises to a peak, then falls away near full draw. The drop from peak to the force at full draw, expressed as a percentage of the peak, is the let-off.
A 100 lb peak with 80 percent let-off holds at 20 lbs at full draw. On a compound bow, this is what lets the archer hold the string at aim. A recurve has no cams, so it has no let-off, and the force simply rises to its peak.
On a crossbow the string is held by the string latch, not by the shooter's fingers, so let-off does not affect how long you can hold aim. It is a cam design characteristic, and on most crossbow product pages it is rarely quoted.
Let-off percentage
Let-off (%) = (peak draw weight - holding weight) / peak draw weight x 100
A peak of 100 lbs that falls to 25 lbs at full draw has 75 percent let-off, because (100 - 25) / 100 = 0.75.
Holding weight for a 100 lb peak
| Let-off | Force lost | Holding weight |
|---|---|---|
| 0 percent (no cams) | 0 lbs | 100 lbs |
| 50 percent | 50 lbs | 50 lbs |
| 65 percent | 65 lbs | 35 lbs |
| 80 percent | 80 lbs | 20 lbs |
Why Let-Off matters
Let-off is often confused with felt cocking effort. They are different things. Let-off is how the limbs load the string at the end of the draw. Felt effort is how much force you apply to cock the crossbow, which a rope cocker or integrated system can multiply.
Understanding the difference stops you reading a bow-style number as a crossbow benefit. When comparing draw weight, the figure that matters for cocking is the peak and the device, not the let-off.
How to read it on a spec sheet
- Treat let-off as optional information. If a crossbow page does not give it, the figure is not necessary for your choice.
- Check whether any "draw weight" figure is the peak or the holding weight at full draw.
- Do not equate a low "felt" weight on a product page with high let-off. It often means an integrated cocking system.
- Look at cam design in reviews, which explains how the force curve is shaped.
- Ignore let-off when comparing recurves, which have none.
Common mistakes
- Assuming high let-off makes a crossbow easier to cock.
- Comparing bow let-off percentages with crossbow figures directly.
- Reading "felt draw weight" as let-off.
- Expecting a recurve to have let-off.
- Trying to adjust let-off yourself. Cam adjustments belong with a qualified technician.
How to tell let-off from cocking effort on a spec sheet
- Find the peak draw weight in pounds.
- Look for any holding or full-draw figure and compute the percentage with the formula.
- Check whether a cocking device is named alongside a lower "felt" figure.
- If a device is named, treat the lower figure as the effort with that device.
- Ask the manufacturer or read the manual if the page does not clarify.
Frequently Asked Questions
What is let-off on a crossbow?
Let-off is the percentage by which a cam system reduces holding force at full draw compared with its peak draw weight. It is a cam characteristic that is rarely quoted on crossbow product pages.
Do crossbows have let-off?
Compound crossbows may have some let-off from their cams, but a recurve has none. Because the latch holds the string, let-off does not change how you hold aim.
How do you calculate let-off?
Subtract the holding weight from the peak draw weight, divide by the peak and multiply by 100. For a 100 lb peak and 25 lb hold, that gives 75 percent.
Is let-off the same as felt draw weight?
No. Let-off describes the shape of the force curve in the limbs. Felt draw weight usually describes the effort you apply with a cocking device, which can be far lower than the true draw weight.
Does let-off affect speed?
Cam design affects how efficiently energy is stored and delivered, but let-off as a percentage is not a speed rating. Compare chronographed FPS for the bolt weight you plan to use.
Why do bows list let-off but crossbows rarely do?
On a bow the archer holds the string at aim, so holding weight matters. On a crossbow the latch holds it, so manufacturers focus on speed, draw weight and cocking effort.
Keep learning
Guides that use this term
- GuideCompound vs Recurve Crossbow ComparedCompound vs recurve crossbow compared on speed, noise, cocking effort, upkeep, cost and accuracy, using four tested models, with clear rules for choosing.Read the guide
- GuideCrossbow vs Compound Bow ComparedCrossbow vs compound bow compared on learning curve, accuracy, noise, cocking effort, repeat shots, upkeep and cost, with clear rules for choosing.Read the guide
- GuideHow to Cock a Crossbow: Rope vs CrankHow to cock a crossbow step by step with a rope or crank, why hand cocking rarely works, and the mistakes that cause uneven strings and injuries.Read the guide
Related terms
- Draw WeightThe peak force, in pounds, needed to draw the string to the latch, which sets cocking effort and is one input to speed and energy.
- CamThe shaped wheel at each limb tip of a compound crossbow that the string and cables run over, creating let-off and a smoother, more efficient release of energy.
- Compound CrossbowA crossbow that uses cams and cables on the limbs to store and release energy, usually with a shorter, more compact frame than a recurve.
- Recurve CrossbowA crossbow whose limbs curve away from the shooter and carry the string directly, with no cams, so the design is simple and often lower in cost.
- Cocking AidA rope or crank device that reduces the effort needed to draw the string and helps it seat evenly in the latch.
- String and CablesThe bowstring that drives the bolt and the cables that link the cams on a compound crossbow, wear parts that need regular inspection, waxing and timely replacement.
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Definitions are general information. Manufacturer figures vary, so follow your crossbow's manual and verify local laws with the relevant authority.