Fix your golf slice with launch monitor data

Last updated: September 12, 2026

By Andrew · Founder of Fore-ward Thinking, a golfer who lives in launch monitor data and built an AI coach that remembers every session.

A slice leaves three signatures in launch monitor data: face open to path, club path out to in, and heel strike gear effect. Each shows up in different numbers, and not every launch monitor measures all three. Identify which signature is loudest in your data, drill for that one cause, hit ten balls, and read the numbers to see whether that cause improved.

What are the three slice signatures in launch monitor data?

The three slice signatures are face open to path, club path out to in, and heel strike gear effect, and each lives in a different number. A slice is rarely one problem, and fixing the wrong one first wastes range sessions.

Many slicers have more than one signature present. The goal is to figure out which one is loudest and fix that one first.

Which slice numbers does your launch monitor actually measure?

Face angle is measured on Trackman, the GCQuad and the Uneekor EYE XO, absent on the GC3, the Launch Pro and the Eye Mini Lite, and estimated on Square and the Garmin R10. Club path is reported on more units than face angle, and a number that is estimated rather than measured carries a wider margin of error. The table below covers the two club delivery numbers that matter most for diagnosing a slice: face angle and club path.

Every unit in the table reports a spin axis, but on the Garmin R10, on a Mevo into a net with nothing on the ball, and on the Square Home Edition with an ordinary ball, that spin axis is itself an estimate. Start line is measured on all of them. Where spin axis is measured, you have what you need to strongly infer whether the face was open even when face angle is missing. For a per device breakdown of every metric, use the free accuracy tool.

A face to path number built on an estimated face inherits the estimate. On units where face angle is estimated rather than measured, you get a more reliable slice diagnosis by reading spin axis plus start line directly.

How do you read face to path when your unit has no face angle?

You read it from two ball numbers, spin axis and start line, on any unit that measures spin axis.

The ball starts near where the face was pointing at impact. If the start line is consistently right of your target (right handed golfer), that is consistent with an open face. The spin axis tells you how much the face disagreed with the path. A positive spin axis (tilted right for a right handed player) is consistent with the face being open relative to the path. Spin axis, explained covers the thresholds and how to read the number on your unit.

When you combine a rightward start line with a positive spin axis, you have strongly inferable evidence that the face was open to the path. You cannot say by exactly how many degrees without a measured face angle, but you can confidently say that closing the face is the fix to test first.

Is your club path out to in, and does it matter?

Path contributes to the slice, but a zero path does not fix it. Zero is a reference point, not a target. A path of 0.0 with the face even slightly open still produces a slice.

If your unit reports club path (see the table above), look at the number across a set of ten or more shots with the same club. A consistent leftward path (negative or "L" values for a right handed golfer) combined with a positive spin axis points to an out to in swing contributing to the slice. But the face to path gap is what curves the ball, not the path number alone.

Path is measured on Trackman, the GCQuad, the Uneekor EYE XO, the GC3, the Launch Pro with its club data tier, the Eye Mini Lite with stickers, and the Mevo+ or Mevo Gen2 with the Pro Package. On the Garmin R10, Garmin does not say whether path is measured or calculated, so the accuracy tool files it as a hint rather than a number to coach off. A small path number on a unit that estimates or does not classify path is not a finding on its own. Look for a consistent direction across ten shots rather than the size of any one reading.

For the full mechanics of how path and face combine to create every ball flight shape, see Club path and the golf ball flight laws. That page covers the geometry. This page is about which number to fix first.

Could a heel strike be adding slice spin through gear effect?

Yes, if you are striking the driver toward the heel, gear effect alone can add enough slice spin to curve the ball offline even with a reasonable path and face angle.

Gear effect is strongest on drivers and fairway woods, where the center of gravity sits well behind the face. A heel strike causes the face to rotate open at impact, tilting the spin axis and adding sidespin. This is a strike pattern problem, not a swing path problem, and it requires a different fix.

If your unit reports impact location, a consistent heel side pattern is measured evidence. If your unit does not report impact location, a driver smash factor consistently below about 1.45 is weakly inferable evidence consistent with a glancing or off center strike. A well struck driver produces a smash factor of 1.45 to 1.50 (Trackman's published tour averages put the tour driver near the top of that range). Low smash does not prove a heel strike on its own, because a toe strike or a thin strike also lowers smash. But combined with a positive spin axis and a slice ball flight, low smash strengthens the heel strike hypothesis.

To check this hypothesis without impact location data, put foot spray or impact tape on the driver face and hit ten balls. If the marks cluster toward the heel, you have your answer.

How do you fix a slice one cause at a time with the ten ball loop?

You fix a slice by isolating one cause, drilling for it, hitting ten balls, and reading the numbers to see whether that cause improved. Do not stack multiple swing thoughts.

1. Pick one cause from your data. Look at your launch monitor numbers and decide which signature is loudest: face open to path, path out to in, or heel strike. If spin axis is the biggest outlier, start with the face. If path is extreme and the face is only slightly open, start with path. If smash is low and the pattern is heel side, start with the strike.
2. Choose one drill that targets that cause. A single mechanical drill, not a swing thought layered on top of another swing thought. Your instructor or a coaching tool can suggest one. The point is: one drill, one intent.
3. Hit ten balls with that one intent. Do not judge by feel. Do not judge by where the ball went on one shot. Ten balls gives you a small sample, and a sample is better than a single swing.
4. Read the numbers, not the feel. After ten balls, look at three things: spin axis moving toward zero, start line moving toward the target, and dispersion tightening. Carry often changes when the strike changes, and a drop is not automatically a loss. Judge spin axis, start line, and dispersion first, and let carry settle over a few sessions.
5. If the numbers improved, hit another ten to confirm. If they did not, try a different drill for the same cause. Do not add a fourth swing thought or switch causes. The next drill, not more effort on the same drill.
6. Confirm across two or three sessions. One session is noise. Two or three sessions with the same improvement is a real pattern. Only then move to the next slice cause.

The value of the loop is reading the ball data for the cause. Feel is unreliable. Ball flight is hard to judge indoors. The numbers are the referee.

How do you know the fix is real and not just one good set?

One session is noise. Two or three sessions with the same improvement is a real pattern.

After a good ten ball set, do not declare the slice fixed. Come back the next day (or the next session, if you are on a simulator) and run the same drill with ten balls. If spin axis, start line, and dispersion are still improved, you have confirmation from a second session. A third session with the same trend means the change is holding.

If the numbers regress in the second session, that does not mean the drill was wrong. It may mean the change has not become automatic yet. Run the drill again. If the numbers come back, continue. If the numbers stay regressed across the second and third session, the drill is not addressing the root cause, and it is time to try a different drill or look again at which signature is loudest.

Once one cause is confirmed improved across sessions, move to the next slice signature and repeat the loop. Check strike first, because a heel strike can print the same curve as a face or path problem. Then face to path, then path. Your data decides the order after that.

I built Chip so the loop above does not depend on my memory. It reads your ball data, interprets what the numbers say about the root cause of your miss, gives you a drill for that cause, has you hit ten balls, then reads the next session to see whether that cause improved. If it did not, the next drill. It coaches from data, not swing video. Free to start with your own export and three messages, no card required.

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