“Flex” refers to the ability of a golf shaft to bend during the golf swing.
Unfortunately there is no official standard measurement of the flex / stiffness of a shaft. Some producers use their own codes (like Miyazaki’s IFC), but many manufacturers use popular stiffness scale, with grades expressed as a single letter:
- L (Ladies) – the most flexible, designed for women or high handicapers
- A or M (Amateur, Moderate, Mature) – designed for seniors or mid-high handicapers
- R (Regular) – designed for average male player, mid handicapers
- S or F (Stiff, Firm) – designed for low handicapers
- X or T (eXtra stiff, Tour) – designed for scratch or professional players
The lack of one universal standard means that two models designated as Regular by two manufacturers may differ from each other and the one company’s Regular may be more like the Stiff than the Regular of another company.
Sometimes, for marketing reasons, a “slight overstiffing” can be observed in the marking of the shafts. Simply speaking the “Stiff” shaft sounds better for some golfers’ ego than the “Regular” one, although the actual flex of both shafts is similar.
Nevertheless there are published tables that determine the appropriate shaft flex / stiffness for a given golfer from the total shot distance, carry distance or swing speed. The averaged values of various criterions presented in the table below can help in the choose of proper flex.
Distances are given in yards, speed in miles per hour.
|150-yard club||8i - 9i||6i - 7i||5i - 6i||4i||3i - wood|
|driver - carry (in the air)||>245||210-245||170-210||135-170||<135|
|driver - total distance||>275||240-275||200-240||180-200||<180|
|driver - swing speed||>110||95-110||85-95||75-85||<75|
|5-iron - carry (in the air)||>175||145-175||115-145||90-115||<90|
|6-iron - total distance||>175||155-175||130-155||100-130||<100|
|6-iron - swing speed||>90||80-90||70-80||60-70||<60|
update: October 2020