What Is Cam?
The 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.
Cam: definition
Also called: cams, cam system, cam timing, eccentric wheel
A cam is an oval or irregularly shaped wheel mounted on an axle at the tip of each limb on a compound crossbow. The string and cables wrap around the cams. Because the cams are not round, the force you feel and the force the bolt receives change through the draw, unlike a recurve where the string attaches directly to the limb.
The cam's shape gives a compound its characteristic force curve and its let-off, the drop in holding force near full draw. It also allows more stored energy to be delivered to the bolt in a shorter frame, which is why compounds can be fast and narrow at once. Brand names for cam systems are marketing terms, so compare measured speed and reliability rather than the name.
Cams must be synchronised, a condition called cam timing. If one cam rolls over earlier than the other, the string leaves the rail unevenly, which can affect accuracy and wear. The TRX Ultra review notes that its 8mm Zero-Torsion axles held cam timing without measurable drift through the testing period, a sign of a stable design.
Cam-related terms
| Term | Meaning | Why it matters |
|---|---|---|
| Cam timing | Both cams rotating in sync | Even string travel, consistent shots |
| Let-off | Drop in holding force at full draw | Easier cocking feel on some designs |
| Axle | Shaft the cam turns on | Wear or play affects timing |
| Cam lean | Cam tilting out of line | Can twist the string path |
Why Cam matters
Cams largely decide how smooth and efficient the power delivery is. A well-timed cam system lets the string travel straight and the limbs release their energy evenly, which supports speed and repeatability.
Cams are also a maintenance point. They carry the strings and cables, they turn on axles that can wear, and misalignment can show up as erratic groups, a string that sits off-centre or visible fraying.
How to read it on a spec sheet
- Look for the cam name and what the maker says it does, then check independent testing for evidence.
- Note any statements about cam timing, axle size or synchronisation features.
- Check whether string and cable replacement requires a press or dealer service.
- Compare listed fps and power stroke, because the cam is only one factor in speed.
- Read the manual's inspection interval for the cam area and the string and cables.
Common mistakes
- Adjusting cams or cables at home without the correct tools and guidance.
- Ignoring a cam that looks tilted or a string that sits off-centre.
- Using the wrong lubricant on axles or cams.
- Treating a cam brand name as proof of better performance.
- Cocking the string unevenly, which strains the cam system.
How to visually check cams
- Uncock and unload the crossbow and engage the safety.
- Look at both cams from the front. They should look matched and sit square to the rail.
- Check for string or cable fraying where it leaves the cam groove.
- Look for play at the axle by gently, safely checking for movement with the crossbow uncocked.
- Compare string position side to side at rest.
- Contact the dealer or maker if anything looks uneven.
See it in our reviews
- TenPoint TRX Ultra — rated 4.9/5
- Ravin R29X — rated 4.8/5
Frequently Asked Questions
What does a cam do on a crossbow?
A cam is the shaped wheel at each limb tip of a compound crossbow that the string and cables run over. It shapes the force curve, gives let-off and helps deliver energy to the bolt efficiently.
Do recurve crossbows have cams?
No. A recurve has the string attached to the limb tips directly. Cams are specific to compound crossbows and add parts to maintain, which is a trade-off for greater efficiency.
What is cam timing?
Cam timing means both cams turn in sync so the string leaves the rail evenly. Out-of-sync cams can cause inconsistent shots and extra wear, and correcting them usually requires a dealer or the manufacturer.
Can I fix cam timing myself?
Usually no. Adjusting cables and strings needs correct tools and a press in many designs. Follow your manual and use an authorised dealer or the maker for any cam or cable work.
Is HeliCoil a type of cam?
No. In our reviews HeliCoil is Ravin's name for its built-in cocking system, not a cam. It is mentioned next to cams because both are brand terms, so compare measured speed and cocking effort rather than the name alone.
Are cams noisy?
Cams contribute to sound and vibration, but string, limbs, dampeners and bolt weight also matter. See noise and vibration for how to compare it, and treat quiet claims with some caution.
How do I know if a cam is damaged?
Signs include a visibly tilted cam, play at the axle, fraying where the string leaves the groove or a change in how the crossbow shoots. Stop using it and have it inspected.
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
- GuideHow to Maintain a CrossbowHow to maintain a crossbow: string waxing, rail and moving-part lubrication, bolt inspection, storage, and when to see a technician.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
Related terms
- Let-OffThe percentage by which a compound's cams reduce the holding force at full draw compared with its peak draw weight.
- LimbThe flexible arm on each side of a crossbow that stores energy when the string is drawn and releases it to push the bolt forward.
- 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.
- Power StrokeThe distance the string travels from its cocked position to rest, which sets how long the limbs have to accelerate the bolt.
- 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.
- Noise and VibrationThe sound and hand shock a crossbow produces when it fires, shaped by limb damping, string silencers, mass and bolt weight.
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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.