How To Change Draw Length On A Compound Bow
Adjusting the draw length on a compound bow requires matching the specific cam system architecture of your model, using precise SAE or metric hex wrenches, and verifying proper bow press safety when cables must be manipulated. Getting this measurement right ensures optimal skeletal alignment, consistent anchor points, and maximum kinetic energy transfer downrange.
Pre-Operation & Equipment Checklist
Modifying your compound bow draw length demands patience, correct tooling, and an understanding of your specific bow's cam design. Whether you are dealing with a rotating module system, a binary cam layout, or swapping out entire module components, proper preparation prevents stripped fasteners, cam damage, and out-of-spec timing issues.
- Essential gear, tools, and materials: Standard fractional and metric Allen wrench (hex key) sets, a portable or bench-mounted bow press (if required for your specific cam type), a T-square or bow square, thread-locker (blue Loctite 242), and a smartphone for reference photos.
- Mandatory prerequisite knowledge and standards: Familiarity with your bow manufacturer’s specific user manual, an understanding of let-off, and the ability to measure your wingspan or wingspan-derived draw length accurately.
- Estimated budget and duration benchmarks: Zero cost if you already own the correct hex keys and rotating module system; 20 to 45 minutes of focused workbench time depending on whether a bow press is necessary.
Step-by-Step Draw Length Adjustment Workflow
Step 1: Measure Your Current Setup and Determine the Target Length
Begin by verifying your exact current draw length by measuring from the deepest part of the bow grip (the pivot point) to the nocking point on the bowstring at full draw, then adding 1.75 inches to that measurement. Alternatively, use a draw board to safely draw the bow to your anchor point while an assistant measures your absolute draw length. Write down your current cam setting (e.g., 28.5 inches) and calculate the exact module position needed to reach your target dimension (e.g., 29 inches).
Pro-Tip: Always measure your physical wingspan in inches, divide by 2.5, and cross-reference this baseline with your measured full-draw form to confirm your target draw length before adjusting your equipment.
Step 2: Identify Your Cam Architecture and Determine Press Requirements
Inspect your bow's cams to determine how length adjustments are achieved. Modern compound bows typically utilize one of three designs: rotating modules (where you simply loosen a retaining screw and rotate the module to the desired letter or number), interchangeable draw length modules (which must be unbolted and replaced with a different size), or peg-adjusted systems (where a stop peg is moved to a corresponding numerical slot).
Warning: Never attempt to remove module screws or adjust limbs on a bow under tension. If your specific cam design requires slack in the cables or strings to access module screws, you must secure the bow in a certified bow press and back out the limb bolts evenly until the cable tension is fully relieved.
Step 3: Remove Fasteners and Adjust the Cam Modules
Using the appropriately sized hex wrench—often a 7/64-inch or 1/8-inch key—carefully loosen the module retaining screws on both the top and bottom cams. Take note of the exact orientation and position of the module relative to the timing dots or reference marks on the cam body. Rotate the module smoothly until the index mark aligns precisely with the hash mark or letter corresponding to your target draw length. Repeat this exact symmetrical adjustment on the opposing cam to ensure synchronization.
Step 4: Re-Secure Fasteners and Apply Thread-Locker
Once the modules are locked into the correct position, thread the retaining screws back into place and snug them down firmly. Apply a single tiny drop of blue Loctite 242 to the threads of each screw to prevent vibration from backing them out during high-energy shooting cycles.
Warning: Do not overtighten module screws, especially on aluminum or magnesium cams. Stripping the threads inside a cam body renders the entire assembly unfunctional and requires a complete factory cam replacement.
Step 5: De-Press the Bow, Verify Timing, and Test-Shoot
If you used a bow press, slowly wind the press to tension the limbs and return the limb bolts to their original factory poundage specifications (counting the exact number of turns out and back in). Check the cam timing synchronization marks to ensure both cams roll over simultaneously at full draw. Step back to a safe target lane, nock an arrow, and draw the bow slowly to confirm that your new anchor point feels natural and repeatable.
How To Calculate Archery Draw Length at Richard Groves blog
Compound Bow Cam System Specifications and Adjustments
| Cam System Type | Adjustment Method | Bow Press Required? | Timing Sensitivity | Common Manufacturers |
|---|---|---|---|---|
| Rotating Module | Loosen screw, rotate module to target letter/number | Rarely (Depends on screw access) | Moderate | Mathews, Hoyt, Prime |
| Interchangeable Module | Swap module piece for different size | Often Required | High | Bowtech, PSE, Bear |
| Dual-Cam Peg System | Relocate draw stop peg to numbered slot | No | Low | Vintage or Target Models |
Common Mechanical Failures and Field Fixes
- Stripped Module Screw Heads: Caused by using worn-out hex wrenches or the wrong metric/imperial size combination. Actionable Fix: Use a small standard flathead screwdriver hammered lightly into the stripped socket to create a bite, or use screw extraction pliers to remove the fastener before replacing it with a fresh factory-spec socket head cap screw.
- Cam Out of Time After Adjustment: Caused by uneven module placement or unequal cable twist application during press operations. Actionable Fix: Place the bow back in a press, inspect the timing dots on the cams, and twist or untwist the cable yokes to bring both cams back into absolute synchronization.
- Peephole Rotation Shift: Caused by altering the string angle and overall draw length, which naturally changes how the string twists at full draw. Actionable Fix: Shoot the bow 15 to 20 times to settle the string, then press the bow or use a string separator to twist the peep sight into correct alignment at full draw.
Frequently Asked Questions
Do I always need a bow press to change my draw length?
Not always, as many modern compound bows feature rotating modules with accessible screws that can be adjusted while the bow is fully strung and at rest. However, if the module screws are hidden behind the limbs or cables at the rest position, or if you need to swap fixed-size modules on certain models, a bow press is mandatory to safely relieve all tension.
Will changing my draw length affect my draw weight?
Minor adjustments via rotating modules generally do not alter your peak draw weight significantly. However, if your draw length increases substantially, you may feel an increase in the perceived holding weight and a steeper valley, while decreasing draw length can slightly lower your peak poundage.
How do I know if my new draw length is correct?
Your draw length is correct when you can stand upright with a relaxed posture, anchor your index finger comfortably in the corner of your jaw or touch your nose to the bowstring, and maintain a slightly bent bow arm without shrugging your shoulders. If you find yourself leaning backward at full draw, your draw length is too long; if your bow arm is cramped and your chest is closed, it is too short.
Can I mix different draw lengths on the top and bottom cams?
No, the top and bottom cams must always be set to the exact same draw length setting. Setting cams to mismatched lengths causes severe tuning issues, erratic arrow flight, cam lean, and potential structural failure of the string and cable system.
Tune your compound bow with precision equipment and expert techniques to achieve maximum accuracy and downrange performance.
