A couple of weeks ago, I had someone send me a picture of their computer screen with some Trackman numbers on it. The screen showed a shot with a draw relationship between face and path but with a fade spin axis with a driver.
The person asked what some of the possible explanations could be such as gear effect, etc. I asked if they had used something to mark the face. I think they said no and I rattled off a couple of possibilities as to why this may happen. One of the things I mentioned was that the way Trackman measures and displays clubpath doesn’t represent what information is going into the ball.
All sorts of hell broke loose.
Before I go on, at one point I mentioned that the way Trackman measured club path was wrong. This was flippant and inaccurate and I apologize for that. What you will see in just a bit is not inaccuracy but a way of measuring that needs to be constantly adjusted by some amount which varies depending on the club and most likely the golfers style.
We’ve all read or heard about D Plane which generally details the information the ball receives from the club to determine it’s flight. This model is based on some very specific assumptions that I won’t get into in this post but at the end of the day, isn’t a great predictive model of ball flight once impact is taken into account.
One of the big factors in determining ball flight is the club path. This club path is generally described as the 3d movement of the head in terms of left and right and up down. For now, we’ll assume it’s always going forward also. =) This definition is similar to how Trackman and other Doppler radars measure the movement of the head. Based on my understanding, Trackman is measuring the movement of the center of the head as it moves through 3d space. This center of the head or the center of the blob will be different for an iron and a driver. For an iron, that center will be very near the face and for a driver, that center will be an inch or 2 away from the face.
Here’s where the trouble starts. The center of the head is not the piece of the club that runs into the ball. The path of the center of the head will always be different than the path of the face that contacts the ball unless the club is moving in a straight line. The number displayed on the screen to represent club path is very accurate but that number isn’t what the ball experiences.
Here’s an analogy I first heard from Chris Como to help explain what I am saying. Imagine a train going in a circle in counter clockwise direction. The same direction the face is closing for a right handed golfer. Imagine this train has only 2 cars which are the engine and the caboose. Imagine that the front of the engine is the club face and the back of the caboose is the center of the club head. As the train goes around this circle counter clockwise, the direction of the front of the engine is always more left than the direction of the back of the caboose. Bringing it back to Trackman and the number on the screen. Trackman and other dopplers show the direction of the back of the caboose on the screen. The ball experiences the direction of the front of the engine because that’s the piece that runs into the ball. Surely there are many other factor in determining the final spin axis and flight as well.
Here’s a graph from a simulation done by Sasho MacKenzie showing the difference between the path of the center of the face and the path of the center of the blob for a driver. You can see that based on this simulation and the assumptions provided, the path of the center of the club head is further right than the path of the impact point for a right handed golfer. The path was being measured at 100,000Hz near impact.
What does this mean?
This means that unless you are adjusting the path number shown by Trackman or other dopplers by some amount, you are teaching off of the incorrect number and you are possibly hurting golfers.
Here’s the good news. For irons, the path of the center of the head number and the path of the impact point will be much more similar. The points are much closer to each other. The other good news is that the adjustment you’ll need to make to the path number on the screen will tend to be a very similar adjustment for that player. Based on the above graph, you can start to get an idea of how much adjustment is needed. As I mentioned, it may not be the same amount for every golfer but it will be something.
The thing I find most interesting is that this information is at least 6 months old and is being written from a putting coach (me) that has never owned a Trackman or similar Doppler radar. I’m surprised at how many golf professionals and players that own this device don’t know the information I’ve shared with you. I’m sure at least some people will want to respond to this and have questions about this that I doubt I will be able to answer them all. I will do my best. I’m also sure that this will be shared with those constantly talking about how useful the machine is wanting an explanation. I think the machine is very, very useful after the adjustment to club path is made in the professionals head and probably nothing as portable with it’s accuracy. I do wish that this information was more readily available and offered up as it’s for the betterment of golfers.