Figure 22. Tiller should be measured on both limbs.
The tiller of a bow refers to the distance between the string and each limb. The distance on the compound bow is measured at the point where the limb is attached to the handle riser and perpendicular to the string (Fig.22). Consequently, each limb has its own tiller measurement.
Changing the tiller measurement is not necessary in order to tune the two-wheel compound bow, but it can be effective to a small degree in tuning a four-wheel compound bow.
Most manufacturers bend test each limb and match the top and bottom limbs on a given bow. For this reason, limbs on today’s compounds perform near equal amounts of work and are generally well balanced during the power stroke.
Figure 23. Turning the weight adjustment bolts will change tiller measurements.
Making tiller adjustments on today’s compound bows is an easy task. To decrease the top limb tiller measurement, you need only turn the top limb weight adjustment bolt inward (clockwise) (Fig. 23). To increase the top limb tiller, turn the weight bolt outward (counterclockwise). The same adjustments can be made to the lower limb tiller. Please remember that any adjustment to one limb will cause a change in the other limb.
The two-wheel compound bow is a closed-circuit system. In other words, the cable system connects each wheel directly to the other wheel. In this closed system, the limbs are in constant balance with one another. Turning the weight bolt of one limb cannot make it work more or less than the other limb. By changing the weight bolt of one limb, you only succeed in changing the angle at which the handle riser sits between the two limbs.
Set both top and bottom limb measurements equal relative to a string line between axles.
The four-wheel compound bow, on the other hand, is not a closed-circuit system because neither eccentric wheel is connected directly to the other wheel. The return cable from each eccentric wheel is connected to an idler and then to a draw length adjustment bracket. In the four-wheel cable system, changing the weight bolt of one limb can cause the limb to work more or to work less than the other limb. This weight bolt adjustment or tiller adjustment can also cause a slight change in the timing or eccentric rollover.
Tiller adjustments on the two-wheel compound should be made whenever you first adjust the draw weight. To do this, measure the distance from the string to that point where the limb meets the handle riser, then turn the weight adjustment bolts to obtain the desired measurements. Most shooters prefer that the top limb tiller be the same as or one-eighth inch more than the bottom limb tiller. Because both limbs will always work equally on a two-wheel bow, it does not matter what your tiller measurements are, but only that you set them and check them regularly to be sure that they haven’t changed.
Measuring and setting the tiller measurements on a one-cam bow can be done easily if a string is stretched between the axles and used as a reference line, instead of the bowstring being used as a reference point. For your initial tuning steps, I recommend setting the tiller measurements equal. After that, try some other tiller setting to see if you aim the bow better with one setting than another.
TUNING YOUR COMPOUND BOW (Paperback, 5-1/2” x 8-1/2”, 152 pages)
Invaluable bow tuning & shooting tips! High performance tuning for all cams, all compounds!
by Larry Wise, International Archery Champion & Archery Coach
To order TUNING YOUR COMPOUND BOW, go to www.targetcommbooks.com
Larry Wise, a world field archery and national target archery champion, and a good man in the deer woods, is one of the best — if not THE best — archery technicians in the world. He knows the bow tuning and performance problems archers and bowhunters encounter. He’s been there, done that…and SOLVED them.
He has given more than 350 compound bow tuning seminars in 36 states and four foreign countries. He’s now also a top-level international coach.