Club gapping on a golf simulator

Gapping is the distance interval between one club and the next in your bag, and a gapping chart is those intervals laid out end to end. It matters because your bag is a fixed budget. Under the Rules of Golf a player must not start a round with more than 14 clubs, or have more than 14 during the round; if you start with fewer you may add up to the limit as you play. The Rules set no required mix of club types at all, so how you spend the 14 slots is entirely your decision, and a bad answer shows up as yardages you have no comfortable club for.

What a good gap looks like

The interval numbers come from the people who measure them for a living. True Spec Golf, who fit using TrackMan Doppler systems and Foresight Quad launch monitors to learn the distance tendencies of each club in a set, report that slower speed players will tend to see 7 to 9 yards between each club, while higher speed players may see 12 to 15 yards. Their stated aim is 14 effective clubs which all serve a purpose and hit the ball a unique distance and trajectory.

That is a range, not a constant, because the right interval tracks how far you hit the ball. Copying someone else's gaps is the first mistake.

Why carry, and not total

Total distance is partly a statement about the ground.

Broadie and Ko, whose golf simulation model was calibrated against tens of thousands of amateur and tour shots, split every shot into two parts: the trajectory in the air, called carry, and the trajectory on the ground, called roll. How much roll you get depends on the ground conditions - green, fairway, rough or sand - and on the ball's velocity and angle when it hits the ground. Taller grass reduces roll, which is why an identical shot travels further on the fairway than in the rough.

The split moves with the club as well. For tee shots with a driver they report that the carry fraction, carry length divided by total shot length, increases with total shot length, because longer shots land at a steeper angle and roll less. For shots hit from the fairway onto the fairway it runs the other way: shorter shots are hit with more lofted clubs, which launch higher, land steeper and roll less. Shots from the rough carry less spin and roll more once they land.

None of that is a property of your swing, only of where the ball came down. Build the chart on carry and the ground stops voting.

There is measurement support for the same choice. In a 2022 test-retest study, carry distance was among the variables that reached excellent reliability with only one or two shots, while roll distance sat in the group that needed between three and eight. Roll is the slower-settling half of the number, and the less portable one.

Building the chart

That same study is the best public guide to how much hitting a gapping session needs. Ten amateur golfers with a mean handicap of 31.2 hit fifteen swings each with a driver and a six iron across two sessions a week apart, measured on a Doppler radar unit. Ball speed, club speed, carry distance and total distance reached excellent reliability with one or two shots. Overall the authors recommend at least seven swings with the driver and ten with the six iron, and they note that variability in the swing performance of low-handicap players is lower than in high-handicap players, so a better player needs fewer.

Use the typical number, not the best one. Broadie and Ko found that for shots other than putts the distance error often has a negative mean - shots on average finish short of the target - with negative skew, because the furthest a club can go is capped by your physical ability while a bad strike can travel almost nowhere. A chart built from your three best swings with each club describes a bag you do not own, and every yardage in it will be too long.

Hold the conditions still. The same paper reports that distance errors are larger from the rough than from the fairway or tee, larger again from sand, and that relative distance error is roughly constant beyond sixty yards but grows as the shot gets shorter. If every shot in your session came off the same flat lie, your chart is a chart of that lie. That is fine, as long as you know it.

Gaps and overlaps

Two clubs are doing one club's job when their carry numbers are close enough that the spread of each swallows the difference between them. The second club is then not buying you a yardage, it is buying you a coin flip, and one of your 14 slots is doing nothing. True Spec's test is the one to apply: does every club serve a purpose and hit the ball a unique distance and trajectory?

A gap is the reverse, an interval noticeably wider than the rest of your chart. Whether it matters depends on how often you face that yardage - a question about the courses you play, not the chart.

What the chart cannot do is tell you what belongs in the empty slot. It identifies which slot is wrong. Choosing the club, or changing the one already there, is what a fitting is for.

The part that depends on your equipment

Every conclusion here sits downstream of the measuring device. Hitting into a simulator screen instead of a fairway does not change that: the launch monitor reading your swing is still the measuring device. The reliability figures above describe one particular radar unit used with one group of players, so they are a property of that whole arrangement rather than a law of golf. Two charts built on different setups are not comparable, and a device reading systematically long or short moves every carry number on your chart - and if that error scales with distance, it moves your gaps too.

Two more honest limits. A gapping chart is a full-swing document, so it says nothing about the partial shots underneath your shortest full club. And it quietly assumes you hit the club you meant to hit.

GSCaddie builds a gapping chart from your own carry numbers, club by club.