Shaft Flex Calculator

Flex is how much the shaft bends under load. Too soft for your speed and tempo and the head arrives late and closed, with launch and spin drifting up; too stiff and it arrives early and open, with a low, dead flight. Speed sets the rough band; tempo and release decide where inside it you sit.

The letters are labels, not measurements. One maker's Stiff can measure the same as another's Regular, and within a brand the driver, fairway and iron shafts of the same letter behave differently. That is why the result is a shortlist to test on a launch monitor, and why the old "80% confidence" bar was removed: it measured nothing.

Speed bands. The widely published generic driver clubhead-speed bands are used: Ladies under 75 mph, Senior 75 to 85, Regular 85 to 95, Stiff 95 to 105, Extra Stiff over 105. Some guides move the Stiff / Extra Stiff line to 110 mph. Within 4 mph of any boundary the neighbouring band joins the shortlist, which is how that disagreement is handled.

Carry to speed. Driver carry is converted at about 2.35 yards per mph, with a range of plus or minus 0.15. Tour players get roughly 2.45 (TrackMan reports a 115 mph PGA Tour average with carry in the low 280s), most amateurs less because of strike and launch. A 7-iron carry is converted at about 1.85 yards per mph and driver speed taken as 1.26 times 7-iron speed, again from TrackMan tour averages. Estimated speeds are always shown with their range.

Tempo and release never change the primary band. A quick tempo or late release adds the stiffer neighbour to the shortlist; a smooth tempo or early release adds the softer one. If they pull in opposite directions they cancel.

• Hit each flex on the shortlist with the same head and ball, ten shots each, on a launch monitor if possible.
• Judge on dispersion and launch/spin consistency first, distance second. The flex you strike most consistently usually wins.
• Keep weight constant while comparing flex; changing both at once hides which one helped.
• Irons and woods can legitimately end up in different flexes. Test them separately.