Precision Wheel Timing
The following technique provides detailed instructions for obtaining perfect wheel timing on two-wheel compounds. You will require the following tools to perform these adjustments.
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Bow Square |
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Narrow Straight Edge |
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Ruler or Calipers |
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Bow Jig, to pull bow back for measurements. |
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Bow Press, to take tension off of bus cables for adjustment. |
Adjust wheel timing as follows:
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Remove cable guard slider from bus cables. |
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Place Bow on Bow Jig and draw the bow back until one of the bus cables comes in contact with the back side of a cam (see Figure 1 above). Note, it is important that you draw the bow back pulling from the same location as you would if you were shooting the bow. You may need to draw with an arrow on the string to draw from the correct position on your serving. I tie nocking points above and below the nock which allows me to time the wheels with no arrow on the string. |
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Place a bow square on the bus cable as it exits the cam as shown in Figure 3. Use a pair of calipers or ruler to meaure the distance from the axle to the bow square. It is very important that the bow square be placed the same distance from the top axle as the bottom axle when making your timing measurments. As shown in the figure, I chose a distance of 1.5" away from the axle as my reference point. |
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Figure 3 |
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Next lay a straight edge across two fixed reference points on your cam as shown in Figure 4. These reference points will be used to determine your wheel timing. When wheel timing is properly adjusted, the angle represented by these two points will be the same for the top and bottom cams on your bow. |
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Figure 4 |
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You are now ready to measure your wheel timing. Record where the straight edge crosses your bow square. The initial measurement for the top wheel is 8 3/8" on this bow, as shown in Figure 5. You may find that the straight edge does not cross the bow square at a measurable location the first time you attempt to take a meaurement. If this is the case, move the bow square closer or further away from the axle as required to get a good reading. Make certain that you place the bow square the same distance from the axle for the bottom wheel. If your wheels are significantly out of time, you may find that the straight edge never crosses the bow square on the second cam. Adjust the appropriate bus cable in two turn increments until you can obtain measurements for both cams. |
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Figure 5, Top Wheel |
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The measurement for the bottom wheel is 10.5" as shown in Figure 6. This is nearly a 2" difference in wheel timing when measured by this method. Small changes in wheel timing show up as large differences in measured timing using this method. This allows you to make very precise adjustments to wheel timing. |
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Figure 6, Bottom Wheel |
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Given these measurements I chose to shorten the bus cable connected to my bottom limb by two turns. When I rechecked the wheel timing, the top wheel measured 7 1/4" and the bottom wheel measured 7 3/4" for a change of nearly 1 1/2" in wheel timing for two twists of the bus cable (see Figures 7 & 8 below). |
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Figure 7, Top Wheel |
Figure 8, Bottom Wheel |
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Given these measurements I chose to lengthen the bus cable connected to my top limb by 1/2 turn. When I rechecked the wheel timing, both the top and bottom wheels measured 7 1/4" as shown in Figures 9 & 10 below. |
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Figure 9, Top Wheel |
Figure 10, Bottom Wheel |
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When you have completed wheel timing using this method, you should find that the bow has a more solid feel against the wall and is easier to aim. |
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I would like to thank Don Kudlacek and Roland Haggard for developing this technique and passing their knowledge on to me. Don is a current IFAA World Champion and Roland is a former IFAA World Champion. You can't argue with success! I hope you find it as valuable as I have. |
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Good Shooting! |