Smash factor: where the 1.50 ceiling comes from

The whole thing is one division

1.49PGA Tour driver average, TrackMan

Smash factor is ball speed divided by club speed. That is TrackMan's definition, and nothing else is inside it: no loft, no launch angle, no wind. It reports how much of the clubhead's energy arrived at the ball. Swing a driver at 100 mph with a smash factor of 1.50 and the ball leaves at 150 mph, which is TrackMan's own example.

Dividing one speed by the other strips out the units, which is what makes it unusual on a launch monitor sheet: a golfer swinging 88 mph and one swinging 118 mph are marked on the same scale. That scale is narrow. TrackMan's combine averages for male amateurs run from 1.49 with a driver for a scratch player to 1.43 for a bogey player, six hundredths covering the lot.

The ceiling is a rule about the clubface

239 microsecondsCharacteristic time limit, 257 with tolerance

A driver face flexes and throws the ball back at you, and the governing bodies cap how much. Before 2004 the measure was coefficient of restitution, and Andrew Tursky reports the USGA limit at 0.822, with a tolerance that made anything over 0.830 illegal. The test since then swings a pendulum at the face and times the contact, a figure called characteristic time.

Jonathan Wall reports that limit at 239 microseconds, with 18 microseconds of manufacturing tolerance taking the conforming maximum to 257. Nothing in the rules says 1.50, though. Adam Young puts the best a driver can do at 1.5 and attributes it to the construction of the ball and club plus the limits the R&A imposes, so the ceiling follows from the face rule rather than being written down anywhere. Wall also quotes the governing bodies noting that clubs built near the top of that tolerance may pass the limit as they wear, which is why driver heads get tested at tour events.

The figure falls as the loft rises

TrackMan's tour table puts PGA Tour players at 1.49 with the driver and 1.39 with a 6 iron; LPGA Tour players sit at 1.49 and 1.41. A pitching wedge, TrackMan says, should read near 1.25. Loft is the pattern: the more loft the club delivers, the more of the collision goes into spinning the ball rather than sending it forward. The gap between delivered loft and attack angle has its own guide.

The LPGA 6 iron figure sits above the PGA one, 1.41 against 1.39, so the ratio is not a ranking of golfers. TrackMan's later writing concedes the awkward half: smash factor is great for drivers but hard to interpret for irons and wedges, with no standard for a good figure beyond the driver. Below it the number is a trend line against your own readings, not a grade.

A low reading points at the face, not at effort

8 yards shorterHalf-inch-low heel strike, with 5-10 mph more speed

James Leitz of Pinewood Country Club lists what to examine once a smash factor has been judged too low: face to path relationships, spin loft, and impact point location. Effort is not on the list. TrackMan's own account of lost energy names off-centre impact, excessive spin loft or poor contact, all descriptions of how the club met the ball.

Golf.com's RoboTest handed the question to a machine. A driver was set at 95, 100 and 105 mph and struck in the centre, then half an inch, three quarters and a full inch toward toe and heel, and high and low on the face. Centre strikes gained 11 yards from 95 to 100 mph, then only 2 more from 100 to 105, the extra speed having brought extra spin.

The strike reversed the sign of that. Half an inch low and three quarters toward the heel, the ball finished 8 yards shorter even with 5 and 10 mph more clubhead speed behind it. Jonathan Wall puts the loss down to vertical gear effect off the lower third of the face, while the upper third gained yards at both speed increases.

What the ratio is good for, and where it stops

One property makes the number hard to flatter: its ceiling is fixed by an equipment rule, so it cannot be raised by swinging harder, the way a distance figure can. Andrew Rice of Berkeley Hall adds the caveat, though: smash factor is often misunderstood as being representative of only how centered a ball was struck.

Rice's point is that it reports the conversion of club speed into ball speed whatever caused it, and that with some clubs it can read too high rather than too low. Both numbers in it are speeds at the instant of contact, which is what a radar or a camera-based monitor is built to catch. Pebble Swing reads joint angles and the backswing-to-downswing tempo ratio out of video frames, which is a different measurement.