Shaft Bend Profiles

An important goal in clubfitting is to match the shaft bend profile to your swing mechanics. Selecting the best shaft for your swing benefits from understanding how stiffness is distributed along the length of the shaft. These stiffness variations are designed into the shaft to accommodate different forces exerted during the downswing. 

Shaft bending during the swing reflects how variations in stiffness along the length of the shaft interact with each other and with the way you swing the club (technique and mechanics). We can see evidence of these interactions by quantifying shaft deflection and comparing it to a direct measure of strain resistance at multiple points along the shaft.

The figure above shows deflection profiles of four shafts with identical flex measurements at the grip end. The shafts were made by the same manufacturer, have the same weights, and measured as regular (R) flex according to the widely used L,A,R,S,X shaft flex classification. The graph plots resistance to deflection at two-inch increments from the butt when a constant load was applied to the tip.

We see that each shaft deflects differently although they have the same butt flex measurement. The L,A,R,S,X shaft flex classification at the butt reveals little about how the shaft behaves during the downswing. The mid section point here is 26 inches from the tip. The deflection measurements predict different flex values for the mid section of each shaft. 

To understand what caused these differences in deflection we examined strain resistance to a constant load applied at one-inch intervals along the shafts. It's a measurement of the effects on stiffness of shaft wall materials, wall thickness, and shaft diameter. In shaft engineering terms, we measured EI at each point to generate an overall stiffness profile.

We see the EI stiffness profile is similar for each of the four shafts from the butt section to the mid section. But EI profiles diverge widely in the distal region from the mid section to the tip region. At 16 inches from the tip, the shaft represented by the red line is much stiffer than the other shafts.

The EI stiffness peak near the tip region of the "Red Line" shaft acts to increase the resistance to deflection seen in the mid section where the EI measurements show essentially the same values. The "Red Line" shaft at A flex will feel stiffer than the "Orange Line" shaft at R flex.

Taken together the results show that tip region stiffness affects deflection in the mid region through the butt region. Shaft deflection is the result of how all stiffness regions interact.

These four driver shafts perform differently for every golfer we've measured. And every golfer has a distinct preference for one of these shafts. The shaft transmits your swing energy to the clubhead -- your rotational power is the engine of the swing. The goal in shaft design is to find different ways to transmit that energy in response to loading forces in the swing.

Shaft bend profiles are an attempt to understand how differences in shaft engineering design relate to individual swing mechanics. But shaft profiles are no substitute for personal testing with a launch monitor and an understanding of your swing tendencies. The old cliche "if you don't test it's just a guess" still holds true.