Olympic Recurve Arrow Rests - Some Comments

[Joe Tapley]

1. Rest Angle

My own set up guide suggest aligning the rest so it is at 90 degrees to the bow string. It is often suggested in bow set up guides that the arrow rest should be angled upwards. So why the difference and does it matter?

The presumed reasons for the suggestion to angle the rest upwards is to stop the arrow falling off the rest either resulting from how the archer draws the arrow or from wind blowing the arrow sideways off the rest. An alternatively reason is that with a sloping rest arm the arrow shaft stays in contact with the pressure button keeping the shaft-button interaction constant from shot to shot. If the problem is the archer then some form improvement is required to solve the problem. Bear in mind that nearly every Olympic recurve bow archer uses a clicker which provides around 70-100 gram force equivalent horizontally on the arrow shaft towards the riser keeping it on the rest and against the pressure button. As the typical button spring pressure is around 300-400 gram force equivalent then there are no issues with clicker usage.

In describing rest arms there are a number of relevant angles:

1. The angle the rest arm makes the horizontal (ground).
2. The angle the rest arm makes with a horizontal plane at 90 degrees to the vertical riser.
3. The angle the rest arm makes in the vertical plane relative to the vertical bow plane.

So the angle referred to in the discussion above is angle number 2. If the riser is held vertically then angles 1) and 2) have the same value.

When shooting a bow at say 70 meters distance the bow riser is tilted at around 5 degrees say to the vertical. So assuming the normal wire on a pivot type rest then if the rest is at 90 degrees to the string (angle 2=0) then the rest wire slopes upwards at an angle of 5 degrees (angle 1). As gravity acts vertically downwards it means that this 5 degrees is equivalent to having a rest sloping upwards with the riser vertical. So there is no real need to have a rest wire sloping upwards as it happens naturally as the bow is raised. The more the riser is tilted the greater the gravity effect in keeping the arrow shaft against the pressure button.

With some modern rests, e.g. the Beiter, the rest arm is fixed at 90 degrees (angle 3) to the bow plane. With the Beiter there is a rest arm slope of around 15 degrees (angle 2). In this case as the riser is rotated from vertical to horizontal the angle of the rest arm to the ground (angle 1) decreases from the basic slope angle 2 to zero. So the Beiter rest acts in the completely opposite way to the normal wire on a pivot rest in terms of how gravity keeps the shaft on the rest and against the button as the riser is rotated in the vertical plane.

As we'll see when we get into the pressure button/rest reaction the ideal geometry for a normal wire arm on a pivot is for the slope of the rest arm in the vertical plane(angle 2) to be same as the slope of the arrow shaft, i.e. vertically the wire rest arm is parallel to the long axis of the arrow shaft. So my suggestion regarding arrow rest alignment is not perfect but is a compromise between no vertical angle between shaft and rest wire and the excessive angle you get if you deliberately slope the rest arm upwards.

2. Rest Angle Dynamic Effects

During the shot the arrow shaft exerts a horizontal force on the pressure button and a downward force on the arrow rest arm. The horizontal force depresses the button and consequentially the arrow shaft on the rest moves towards the riser. The arrow shaft support point on the rest moves rearwards towards the rest arm pivot. The amount the shaft moves on the rest arm towards the rear of the riser depends on angle between the rest arm and the bow plane (angle 3). With the Beiter rest (angle 3 equals 90 degrees) the shaft support point stays in the same. If the rest arm angle 3 approaches zero (a wrap around rest) the the shaft support point moves the maximum amount backwards. With a normal arrow rest the shaft moves some distance between these two extremes. The closer the rest arm pivot point is to the pressure button then the larger angle 3 becomes and the less the arrow support point on the rest shifts.

There are two possible consequences of a shift in the shaft support point when the pressure button is depressed:

• The first effect applies only with wrap around rests where the rest arm is close to parallel to the bow plane. It is simply that if you have a very thin arrow shaft (NanoPro, X10 say) then when the button is depressed the arrow shaft can drop into the wider gap between the rest wire and the button and get jammed. Where this happens the fletchings are likely to be damaged as there is a restraint in the shaft horizontal flexing.

• The second effect occurs whenever there is a vertical angle between the rest arm and the arrow shaft (different values of angle 3). With an angled rest the front of the rest is higher then the back of the rest. When the button is depressed and the shaft support point on the rest moves rearwards (and therefore downwards) the front of the arrow rotates downwards (gravity and the vertical force from the release). It follows that when the shaft sub-sequentially flexes away from the riser the shaft is flicked upwards by the rest. Clearly having an excessively long rest arm is going to make this problem worse.

The way to avoid rest interference with the arrow shaft is:

1. To have the arm pivot point as near to the pressure button as possible.

2. To have the rest arm angle slope (angle 3) the same as that of the arrow shaft. In this case although the shaft support position still shifts when the button is depressed there is no consequent downward rotation of the arrow shaft and no subsequent flick upwards from the rest when the arrow shaft moves away from the riser.