The flex number is awarded to a vaulting pole to help Pole Makers produce consistently the same pole as is in the field. Keeping consistency over the years is important to ensure the pole is cured and produced in the oven with as many consistent variables as can be maintained. The same pattern, the same resin percentage, stable heat and humidity, and other natural variables that affect the outcome of the pole. Any variant of the pattern will change the pole's stiffness.
The origin of the flex system for vaulting poles was introduced to the industry by Herb Jenks carried over from the defection measure of an arrow shaft's spine. He designed a vaulting pole with multi-variable sail wrap widths that changed the stiffness of the pole. His original setup was strictly to measure the sail wrap. this measured 6 inches up from the butt of the pole and right at the tip of the top of the sail piece. (See Photo image to the right) and required a set span that matched the sail's length for each length. A 144" (12' ) span for 14' poles was what he started with. When hanging a 50 lbs weight from the middle of the span on the vaulting pole, the pole deflected in inches (") today converted to centimeters (cm). Altius still uses Inches. Those can be converted.
When the Pole is positioned on the span 6" from the butt end and the full span length, the less friction that ...can achieve yields with the most accurate measure; believe me when I say this is a good system. It is used by many trying to perfect it to an exact measure that an engineer in the business would seek. Yet, please do not lose any sleep over being a perfectionist, as you will never get an exact number. The system has flaws and knowing that I have found that if you strive to make a pole with a mid flex number, you can eliminate pole crossover weight ratings. This will help you to move from one pole to another. A measure if (") of .1 or 2.5 (cm) is about a 1 lb. difference and why people get so wrapped up in the most accurate flex number that can be over come by just raising or lowering the hand grip, 1 or 2 inches.
Weight ratings are always very similar, from Brand to brand one Brand, Sometimes 3 lbs. to 5 lbs. softer or stiffer. This difference is based on two things:
In the past, Pole Makers used to measure the weight load of 140 lbs., but call it a 130 test to add what was called back in the day a "fudge factor" (a calculation to account for error or unanticipated circumstances.) They also made poles with the sailwrap longer and higher than today. This made the pole hard for novice vaulters to bend and those that may have bought a pole longer than their ability. (defined as a pole 18" above the vaulter's best ability.) We have a true-weight rating with no "fudge factor". Bending a pole is necessary only after you have learned how to swing on the pole. The process has to be easy, or you will be thrown back down the runway. Let a qualified FiberSport reseller help you to be fitted to a pole. You will jump higher and save money on poles.
Since 1980. improved designs in the sail wrap design to facilitate the pole to roll-over better, allowing athletes to capture the ride (So to speak). Improved resin systems to coat and impregnate the fabric improved in 1989. IN 2012, Improved consistency fabric weaving of fabric. I introduced a better compaction system to eliminate air voids in the fabric and seal the pole. This has proven to be the answer to "the Durable Vaulting pole."
We have studied this and have introduced the idea at ASTM meetings to no avail. Far too many variables and variances, plus engineering ideas, seem to overthink this, in my opinion.
Reasons why not!
1. The span to support the pole is different with each manufacturer.
Some measure bigger spans and more of the pole. Some think this is better. They have forgotten it is a SAIL WRAP measurement.
2. Some use a weight in pounds and others in kilograms. (22K does not equal 50 lb.)
3. Some measure from 6" from the butt of the pole and others from 12".
4. Many have had their FLEX NUMBER out in the marketplace for years, and to change or adjust at this point would be devastating to matching future poles to what you are using.
SOLUTION: Very SIMPLE - Only compare flex numbers between the same brand, not other brands. Pay attention here. When you go to the next length pole, there is a new span.
(PLEASE NOTE: Don't sweat the little stuff! The difference between 21.0 and 21.3 is 1 lb. and a 21.0 to a 21.6 is almost 2 lbs)
adjust your grip up or down to average this! (1" = 1lb to 2lb depending on the brand)
If you measure more of the pole, you will get a more significant number than the rest of the brands. Your stiffness number is measuring, not the sail, but the pole itself & areas of the pole that do not bend. Is that more accurate? We feel the sail measurement we use may not equate to others but is more accurate!
