Does ClubWatch Affect Your Swing?

It's a natural question for golfers to ask whether ClubWatch units will affect their swing. The short answer is:

No, ClubWatch will not affect your swing in any perceptible way.

Here we'll explain why.

First we need to talk about swingweight vs. MOI.

MOI

The dynamics of a golf club swing are best characterized by Moment of Inertia (MOI), a property determined by distribution of mass (weight) at various distances from an axis of rotation – specifically it's the sum (or integral if you want to do calculus) of all mass multiplied by the square of its distance from the axis. In the case of a golf club, that axis is near the end of the grip where your wrists hinge. Put another way, "MOI is a basic physical quantity which represents the heft that resists rotational acceleration of the club around the wrist hinge of a golfer." Measuring and adjusting MOI (and matching MOI across different clubs) is the correct way to approach club dynamics, but this requires a specialized device that was only invented recently.

Swingweight

Long before the invention of MOI measurement devices, people wanted a way to characterize and adjust club dynamics, and since they didn't have a good way to measure MOI, they came up with a proxy called swingweight, but it's actually not a very good proxy:

"Swingweight is an arbitrary measurement of the relationship of weight in a golf club about the 14-inch fulcrum point on a swingweight scale" — i.e. the relative weight of the two portions of a golf club on either side of a point 14" from the end of the grip. It "doesn't represent anything really physical in a golf swing."

But it is easy to measure without any high-tech devices, just requiring a simple mechanical scale. An excerpt from one article tells us more about it:

Back in the 1920s when swingweight was developed, its originators were aware of the principles of MOI matching and tried to make swingweight matching of clubs simulate MOI Matching. They failed because the principle of the swingweight scale they developed could not truly accomplish the task of measuring the MOI of a golf club. Over the decades since the development of swingweight, engineers familiar with the principles of MOI have been in agreement that MOI matching would truly make all clubs within a set swing with exactly the same feel, while swingweight matching could not.

So now that we know MOI is the right property to care about, we can consider how much ClubWatch affects MOI. Recall that MOI is given by mass multiplied by distance from the rotation axis squared. A ClubWatch unit is 7 grams, but its distance from the axis is effectively zero, so it does not change the MOI.

Now, even though we know swingweight is not a very meaningful property to describe swing dynamics, we can still calculate the effect, out of academic curiosity. The convention is that adding 5 grams to the grip subtracts one point from the swingweight along a 60-point scale (A0 to F9). Since a ClubWatch unit is 7 grams, installing one would reduce swingweight by a bit more than a point. As mentioned, since this is at the grip end, it should be disregarded in terms of the true dynamics / MOI proxy. Furthermore, even for impactful swingweight changes made to the head of the club (adding 2 grams to the head adds one point to swingweight), double-blind tests have shown that the majority of golfers can't tell a 2–3 swingweight point difference.

Key takeaways

• A ClubWatch unit does not affect the true property of swing dynamics: MOI.
• The effect on swingweight can be disregarded since the change is at the end of the grip.
• Even for a more legitimate change to swingweight — like adding or removing mass at the club head — the change from a ClubWatch unit, ~1 point on a 60-point scale, would not be noticeable.