The rule everyone quotes — and its limits

The published guidance is familiar. Senior flex for driver speeds around 72–83 mph. Regular flex for 84–96 mph. Stiff for 97–104 mph. Extra-stiff above 105 mph. These ranges are drawn from years of industry fitting data and they're a useful starting point.

But MyGolfSpy's independent shaft-flex laboratory test found something the rule-of-thumb misses: swing speed alone is only the start. Testing a mixed group across multiple flexes on a FlightScope launch monitor, they reported no single consistent trend. Fitting purely on clubhead speed would have cost their highest-speed player 9 mph of ball speed. Nine miles per hour. That's fifteen to twenty yards of carry, gone, because a speed chart said one thing and the delivery said another.

Why speed alone doesn't finish the answer

Two golfers with identical 92 mph driver speeds can need different flexes. A smooth, unhurried transition loads and releases a Regular flex cleanly — the shaft has time to bend and recover. An aggressive, fast transition at the same speed will typically overpower Regular flex and want Stiff. The variable is tempo. Neither golfer is wrong; the fitting is different because the swings are different.

The other variable is where in your swing the shaft loads — at the top of the backswing or during the downswing. That's what makes shaft fitting genuinely a fitting rather than a chart lookup. Two shafts labelled the same "Stiff" from different manufacturers can behave measurably differently.

The two mistakes that repeat

The first is ego-fitting. Playing Stiff because it "sounds better" than Regular. If your true driver speed is 88–92 mph and you're in a Stiff shaft, you're likely losing launch height, spin, and carry — and probably fighting a slice the shaft is quietly amplifying. Regular flex isn't a downgrade; it's a match.

The second is assuming one flex covers the bag. Driver, fairway woods, and irons all generate different speeds and load the shaft differently. Many well-fitted golfers play different flexes across the set. Wedges, in particular, are often built with heavier or stiffer shafts to improve short-shot control.

The honest test

If you don't know your actual driver swing speed, you're guessing about every equipment decision downstream of it — not just shaft flex, but ball choice, loft, and club selection. A launch monitor session or even a basic speed measurement at a fitting centre solves that in fifteen minutes. Then take your tempo and delivery into the conversation with a fitter. The chart is a starting point. The fitting is the finish.

Coming next

Loft Creep — Why Your 7-Iron Isn't What It Used To Be

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