The first thing to know about comparing the flex of golf shafts is the industry has no standard. A shaft rated as a stiff flex by one manufacturer may feel as soft as another company's regular shaft, and the flex factor is made more complex when including the choice between steel or graphite for the material.
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Distance vs. Accuracy
Most shaft manufacturers recommend stiff shafts for players with swing speeds of 95 mph or faster. A club moving at that speed is fast enough to deliver distance, and the stiffer shaft helps with accuracy. For players with slower swing speeds, a regular-flex club can help add clubhead speed and, therefore, add distance. Former U.S. Golf Association technical director Frank Thomas says if your drives, for a right-hander, stray dramatically left on full, hard swings, try a stiffer shaft in the driver.
Stiff golf shafts are better for players whose acceleration is built in the last quarter of the downswing, according to one shaft manufacturer. Players who overswing tend to accelerate more at the start of the downswing, and professional players often use a delayed release, in which the wrist cock is held as late as possible to build snap in their shots. For players with a smooth acceleration,fitting a shaft according to clubhead speed at impact is recommended.
Shorter shafts have a stiffer flex, so tipping a shaft, or cutting up to an inch off the clubhead end to a custom length, can slightly change the shaft's flex. Tipping is more common with drivers and fairway metals, whose shafts are commonly made of graphite and longer than the steel shafts used in irons. Tipping graphite shafts makes the tip feel stiffer, but it won't change the overall flex of a regular flex shaft to stiff.
Feel and Balance
Whatever flex of shafts you choose, it's important to build consistency. The driver and fairway metals should have similar flex and feel, as should the irons. While tipping can fine-tune a graphite shaft, irons can be adjusted by "stepping," which means to use a shaft meant for a clubhead one step stronger or weaker. Stepping adjusts a club 1/2 flex, so combining a 3-iron shaft with a 4-iron clubhead, for example, will make it feel somewhat more flexible, and using a 5-iron shaft will make it feel stiffer.
Finding the Right Fit
The best way to find what shaft is best for your swing is to experiment with a launch monitor, which is commonly used at golf stores and pro shops that employ professional club fitters. The launch monitor measures not only swing speed and ball speed, but it also shows you the position of the club face at impact, the ball spin rate and the shot dispersion. Experiment with different shaft flexes for the driver, fairway metals and irons to see which produces the most consistency.