Club path and swing direction are different

Two numbers, and only one of them is an instant

TrackMan defines club path as the horizontal direction of the club head's geometric centre at the time of maximum compression. One instant: the moment the ball is flattest against the face. A positive number means the head was travelling right of the target line, a negative one left, and the sign holds whichever way round you play.

Swing direction measures the same downswing a different way. TrackMan builds it from club head positions across roughly 75 centimetres either side of contact, sampled about 20,000 times a second, and reports the horizontal aim of the plane that arc lies on. Their page states the distinction plainly: club path is the motion at one point in time, swing direction is hundreds of points.

The words coaches use belong to the second number. A negative swing direction is what instructors call over the top, a positive one is under the plane, zero is on plane. So the number a lesson is about and the number that meets the ball are not the same, and a monitor prints both.

Where you meet the ball pulls the two apart

−2.5 degreesSwing direction one TrackMan coach wants behind a straight iron

What separates them is where in the arc the ball sits. Tom Stickney, writing on TrackMan's blog, gives the direction of the effect: hitting down on a short iron moves your true path further right, hitting up on a driver moves it further left. Same swing, different reading at the ball.

Which is why the correction belongs to the club rather than to the golfer. Stickney's rule of thumb is to aim the body a shade left with the short irons and a shade right with the driver, and he notes that Ben Hogan had already got there by feel, decades before any of it was measured.

Coaches ask for the gap in numbers. John Parkinson, a TrackMan University coach in Germany, says that to hit arrow-straight iron shots he wants a swing direction of around minus 2.5 degrees. Minus, for a straight shot: the plane aims left of the target so the descending club is travelling at it by the time the ball is in the way.

The circle you swing on changes with the club

Swing plane, in TrackMan's vocabulary, is the vertical angle between the ground and the circle the club head travels on through the bottom of the arc. A driver typically sits between 45 and 50 degrees. Shorter, more lofted clubs stand that circle up, because the golfer stands closer to the ball.

Club matters here; ability barely does. Alex Bliss and Ben Langdown measured one golfer over three indoor sessions: driver plane 47.8 degrees, 7-iron 58.4, pitching wedge 60.4. TrackMan's Combine averages for male amateurs with a driver run from 48.1 degrees at scratch to 49.4 for a bogey golfer. Twelve and a half degrees between two clubs in one bag; a degree and a third across the whole handicap range.

How much of the start line the face actually owns

76% down to 61%Share of the start line owed to the face, driver to 58-degree wedge

The face and the path split the start line between them, and the split has been measured. Paul Wood, Erik Henrikson and Chris Broadie of PING's engineering department ran 157 golfers past an eight-camera Vicon system and a Foresight unit: 731 driver shots, 745 with a 7-iron, and 99 wedge shots from a low-handicap subset.

Filtered to strikes within a quarter of an inch of the face centre, the ball started 76 percent of the way toward the face angle with the driver, 69 percent with the 7-iron, and 61 percent with a 58-degree wedge. The share falls as loft rises. A swing robot hitting the same 7-iron, path held constant, gave a slope of 0.63.

So the path owns about a quarter of where a drive sets off and nearly two fifths of where a wedge does, more than the tidy coaching ratios allow it. The error has run the other way before: the same paper notes that for years the PGA of America's test required candidates to answer that the ball starts along the club path.

Every path number has somebody's zero inside it

1.5 degrees apartDriver club path, two launch monitors, the same shots

Club path is reported relative to the target line, and a target line is something somebody sets. Bliss and Langdown found one degree of calibration error worth four yards of side dispersion over a 250-yard carry, and the same error lands on the directional numbers. Their two units disagreed on the same shots: driver club path averaged minus 3.75 degrees on the TrackMan, minus 2.25 on the Mevo+.

Tour figures are thinner than the topic deserves. TrackMan's attack angle page prints tour averages club by club; its club path page prints none, offering instead the window the Austrian coach Christoph Bausek prefers, three to six degrees either side of zero. He argues against zero itself: there, the smallest face error tilts the spin axis and bends the ball off target.