Rate of Clubface Closure

The rate of closure of a driver through the impact zone can affect the curvature of the ball flight trajectory. Here's how it works.

As the clubhead approaches the impact zone, the clubhead begins to rotate in a counterclockwise direction. The direction and force of rotation is determined mainly by the action of the forearms/wrists/hands in squaring the clubface to target in preparation to hit the ball.

Counterclockwise rotation of the clubhead imparts a clockwise rotation on the ball. The clubhead and ball rotations resemble the action of two gears. Clockwise rotation of the ball from this gear effect results in a fade ball trajectory.

The above figure illustrates the gear effect generated by rapid closure of the clubhead through the impact zone. The arrows indicate counterclockwise rotation of the clubhead inducing clockwise rotation of the ball.

How fast the golfer rotates the club is a matter of swing style. Two extremes of style can be considered. One style is to rotate quickly at impact in a flip/roll motion that pronates the trail side wrist over (on top of) the supinating lead side wrist. It's a fast rate of clubhead closure requiring exquisite timing for ball flight accuracy.

Flip/roll is often seen in players who remain relatively square to the target line with minimal hip rotation through impact, an open the clubface during the backswing or the transition to the downswing, and often a wide shot dispersion.

The alternative swing style is to delay or hold clubface rotation through the impact zone. It's an action typically seen in elite players who have significant body rotation through impact and a neutral to slightly closed clubface during the swing. Since the clubface is reasonably square to the target line for a longer time prior to impact, this style can yield greater shot-making accuracy.

Gear-like actions are additive in their effects on ball flight, and is the sum of the rate of closure gear effect, the effects of driver face bulge and roll associated with off-center ball contact, and face angle at impact. 

Loft Change Face Angle?

THE PROBLEM. Confusion about the relationship between loft angle and face angle has developed as adjustable drivers have become increasingly popular. Does changing loft angle change face angle? Let's look closely at this relationship to understand effects of changing shaft orientation in these clubs.

MEASUREMENT METHOD. A specialized gauge is the best tool for determining the loft angle and face angle for any club. In measuring a driver, the lowest point of the sole should be centered over an alignment line on the gauge platform. The lie angle is adjusted to position clubface score lines parallel to the platform and perpendicular (square) to the target line.

Loft angles are measured with an analog or digital protractor perpendicular to the score lines, and face angle is measured parallel to the score lines with either a protractor or a calibrated gauge alignment guide.

RESULTS. When the center of the clubface is in the square position, the face angle is at zero degrees. Rotating the driver to orient the clubface a few degrees left of the gauge's target alignment line closes the face position. Measuring the loft angle in the closed position shows a lower number than at square, and the decrease is equal to the amount of negative change in the face angle.

Opening the clubface relative to the square position yields a higher loft, and the increase in loft is equal to the positive change in the face angle.

CONCLUSIONS. Relative to the target alignment line, closing the clubface makes the face angle negative and tilts the clubface forward to give a lower loft reading. Opening the clubface makes the face angle positive and tilts the clubface backward to yield a higher loft angle reading.

The physical relationship between the loft angle and face angle in a fixed position has not changed. But when the clubface is opened or closed, the angle of the clubface relative to the target line on a flat surface under the club is altered: closing the face angle lowers the effective loft, opening the clubface increases the effective loft.

OPTIONS. When the clubface is in the open position, slide a thin wedge of wood or cardboard under the back of the sole. The clubface will return towards square, or closed depending on the thickness of the wedge and how far you slide it. This little trick can be exploited in the design of an adjustable driver -- or when you address the ball on the tee by slightly rotating the club in your hands while preparing for the backswing. 

Clubheads with adjustable sole plates can be adjusted to raise or lower the sole contact point relative to the gauge or turf. The result of these adjustments is to open or close the clubface and compensate for changes in loft. However, once new settings have been fixed in place by tightening adjustment screws, the same loft angle/face angle relationship holds as we previously measured it. It's physics.

The loft angle/face angle relationship holds for all clubs, either with adjustable shaft positions or shafts glued (epoxied) in place. Choose any setting for the shaft hosel alignment in the clubhead and fix the shaft firmly in place by tightening the adjustment screw. Repeat all the above measurements without changing the adjustment settings to confirm that closing the clubface lowers the loft, and opening the clubface increases the loft.

Reshafting a Driver

It's common for golfers to buy a new heavily advertised driver only to find difficulty getting the promised performance. Among the choices of what to do next is replacing the shaft. A new shaft can help but it should be part of a more comprehensive look at your driver performance issues. Here's where to start before spending money on a new shaft.

Check the driver specifications to determine if they match your swing (technique and range-of-motion). If a golfer with an 80 - 85 mph swing speed and a downward angle of attack (AoA) on the ball through impact is swinging a clubhead with a 10 degree loft, distance will be less than the player's potential unless AoA is increased or a higher-lofted driver is played.

Among all the factors that affect distance with your driver, the most important consideration for any given swing speed is launch angle. The ball needs to leave the clubface with a high enough launch angle to achieve reasonable distance. Launch angle is the sum of dynamic loft and AoA through impact. 

Proof of launch angle concept is in the water hose analogy. Aim a garden hose at a distant part of your lawn and turn on the water faucet. Experiment with angle of the hose and force of the water. You soon learn there is an optimum combination of angle and force. The relationship holds for golf clubs because it's basic physics. That's why most pros with good technique hit the ball high off the tee.

How does the shaft affect driver performance? The shaft is the conduit for transmitting the energy of your swing motion to the clubhead. Shaft feel and performance is a function of the way stiffness (flex), torque, and weight is distributed through the shaft. A shaft matched to your swing traits will improve driver performance. Clubhead loft and AoA determine the type of improvement you can expect from a new shaft.

Effective shaft fitting requires the use of an accurate launch monitor. We prefer to use a radar launch monitor because it provides a direct measure of clubhead path and ball flight (including launch angle, ball spin, ball trajectory). We find it's the most accurate way to determine how shaft variables match your swing characteristics.

Shaft variables include stiffness distribution (flex) from tip to butt, torque, weight (and weight distribution), materials (graphite fiber composition, engineering design, and manufacturing methods), length, and the most elusive one of all: feel. It's probably the most important reason why you should test shafts personally. There is no subsitute for personal testing.

Flex (stiffness) is probably the most misunderstood shaft variable. Shaft engineers often design variations in stiffness through the length of the shaft to affect feel, the shape of ball flight trajectory, and ball dispersion. An easy way to think about it is to consider distinct performance zones along the length of the shaft with a different flex in each zone. The EI curves on our web site reveal the wide variation in stiffness zones that we identify in modern shaft designs. 

The best flex distribution for you will depend on your individual swing mechanics. For example, do you have a fast overall tempo -- do you start the downswing with a fast action -- is your swing rhythm smooth -- do you swing down or up through impact? Optimizing flex in each zone for the particular way you swing the club will make a substantial difference in its performance. There is no stock solution for everyone.

The bottom line: the right shaft for your driver is best determined by understanding how you swing the clubhead through impact. The most effective shaft fitting requires testing with a radar launch monitor and an evaluation of your swing mechanics. This integrated approach is the best way to help you increase distance and accuracy, which is the reason most golfers reshaft their drivers.

KVest Swing Coordinates

K-Vest motion capture sensors measure rotation in degrees per second of the pelvis, thorax, and lead hand during the golf swing. Rotational velocity is detected around three local axes in each body segment. To help visualize the axes and the movements, consider the right hand rule. 

Extend your right hand in front of your body and make a fist. Then, point your right thumb up, thrust your index finger forward, and point your middle finger to the left. Your thumb, index finger, and middle finger will be oriented 90 degrees relative to each other. The thumb is the z-axis (open and closed rotation), the index finger is the x-axis (side bend), the middle finger is the y-axis (forward/backward bend).  

Here's how pelvis rotation is measured. A 3D motion capture sensor is placed next to the sacrum of the pelvis to detect rotation around the vertical axis (z-axis) oriented along the base of the lumbar spine. The z-axis is perpendicular to the transverse anatomical plane that bisects the body into upper and lower halves. Rotation around the z-axis opens the pelvis to the target on the downswing and closes the pelvis on the backswing.

Side bend (lateral bend) is measured around the front-to-back axis (x-axis) that runs perpendicular to the sacrum. This axis lies in the sagittal anatomical plane that bisects the body into the left half and the right half. Side bend can be described as rotation around the x-axis. During the swing you tilt the pelvis to one side on the backswing and to the opposite side on the downswing.

Forward and backward bend (flexion and extension, respectively) is measured around an axis (the y-axis) that runs in the left-right orientation through the pelvis. The y-axis lies in the frontal anatomical plane that bisects the body into a front half and a back half. In an efficient address position, you bend the pelvis forward around the y-axis. The amount of pelvis bend changes during the swing.

Similar considerations apply to the thorax and to the lead hand/wrist. Quantifying the rotation of these body segments during the swing reveals their kinematic sequence. It reveals the way these segments move relative to each other that's independent of the forces involved. Optimizing their timing, sequence, and peak speeds during the swing is the essential start of any swing improvement strategy. 

A key advantage of the K-Vest system for swing analysis is its portability. We can take it from the studio environment out onto the range or the course to examine swing mechanics in real world performance conditions. It can be synchronized to our radar launch monitor (also portable) and high speed video for a relatively complete picture of how you swing a golf club.

Where to Start in Fitting

The foundation of a golf swing begins with understanding what governs your range-of-motion. Next comes matching clubs to your range-of-motion. Then comes technique. That's the most effective plan to follow for improving your game. 

The first place to start is measuring and understanding your range-of-motion for the golf swing movement pattern. You need to determine your joint and muscle mobility, and the potential restrictions that might limit your swing motion. Even if you don't follow-up with drills and exercises, learning a warmup routine specific to your needs will improve performance and reduce the potential for injury.

The next step is getting clubs that match your range-of-motion and allow you to swing easily with control and consistency. The clubs should not force you to make unnecessary adjustments in your swing to compensate for poor specifications. We cannot overstate the importance of matching the club specifications to your swing. 

A common problem we see are shafts that don't have the optimum specifications for the golfer's swing. Rarely are general stock shafts in off-the-rack clubs correct for an individual swing style. When you buy a set of irons, be sure you take the 2 - 3 hours needed to optimize the shaft (e.g., length, weight, balance, flex, graphite or steel, etc.) for feel and performance.

Clubfitting requires continuous feedback from the player to get the clubs right. That takes time and testing, and perhaps a follow-up fitting session. Often a test club or two customized to your specifications will be needed to make the final choice. 

And don't forget to have the lie angles on your irons adjusted. Whether you use a ball with a vertical mark (best method) or a lie board (not as good), be sure to include measuring ball flight trajectory with a radar launch monitor. If you are on a range, you will be watching ball flight, but you still need the launch monitor to know if you are maximizing performance.

Getting the lie angles right on your irons is essential if you have any shot dispersion or accuracy issues in your game. Long irons often require different adjustments than short irons, and the wedges frequently need to be more flat than you think. The goal is to adjust lie angles to get the desired ball flight -- the numbers don't mean much if the ball flight is not correct.

Here's the bottom line. Take a little time to learn whether there is something simple you can do to improve your range-of-motion, and get clubs that fit your swing mechanics. Personal testing with plenty of interaction and feedback with your clubfitter will benefit every facet of your game.