Stiffness of a Pole

[sduvinage]

Can someone explain to me why two poles of the same weight can have a different stiffness to it?
Is this even true?
I thought the weight rating of a pole was directly related to its flex rating?

[rainbowgirl28]

Can someone explain to me why two poles of the same weight can have a different stiffness to it?
Is this even true?
I thought the weight rating of a pole was directly related to its flex rating?

Within a specific brand, there is a range of flex numbers that correspond to a weight rating for a given length (it's different for every length).

A 13'150 might have a flex a between 18.5 and 19.0 (I just made up those flex numbers). So a 13'150 might really be a 13'150, 13'151, 13'152, 13'153, or 13'154. Although the manufacturers have patterns they cut the fiberglass in to achieve a pole of a certain weight rating, it can be difficult to get them to come out the same every time for a variety of reasons. They might try to make 10 18.8 poles, and maybe 5 come out as 18.8 and the rest in that 18.5 to 19.0 range. It's especially difficult the smaller the pole gets, that is part of the reason you see the smaller poles in bigger weight increments.

This is a generalization, the flex number to weight ratio also varies with the length and stiffness of the pole, so in the really small poles, 1.5 of flex might translate to about 5 pounds, while in a medium sized pole, it might be 1.0, and for the poles the elites are on, it might be 0.5 or less. Again, those are generalizations to give you an idea, not actual numbers.

Different manufacturers vary in the spans they use to flex their poles, so their numbers are generally not comparable. They each use their own flex number scale to assign a weight rating (because there is more to the resistance you feel than flex numbers, for example, a crossbar has a flex number, but you wouldn't want to vault on one if it was bending more than a tiny bit).

So Manufacturer A might say a 13'150 is anything between an 18.5 and 19.0. Manufacturer B might use a different span, but if their 13'150s were tested on the same span as Manufacturer A, you might find that theirs were between 18.7 and 19.2, and manufacturer C might come out like 18.4 to 18.9.

Studies have been done and it was found that for most poles, you're going to get a similar pole if you order by length and weight rating no matter who the manufacturer is.


But flex numbers do matter, that's why it is important to use them when ordering new poles of the same length as existing poles. I always recommend coaches stay within the same manufacturer if most of their poles in a given length are already the same manufacturer.

For example, in the 12' to 12'4 length there is a lot of variation.
Gill (Skypole/Mystic/Pacer) makes 12' poles in 5lb increments. But in 2003 they tinkered with the flex charts, so an older 12'120 may feel more like a 130. And they didn't always do 5lb increments.
Spirit makes 12'1.5" poles in 10lb increments. So a 12'120 Spirit has a bigger range, it could be as soft as a soft Mystic 12'120, or as stiff as a stiffer Mystic 12'125.
Altius makes 12'4 poles in 5lb increments. I haven't used them much, especially not any made in the past 10 years, so I can't say how they compare.
ESSX makes 12'4 poles in 2kilo increments. In my experience, their weight ratings probably compare a little closer to Gill's 12'6 poles than Gill's 12' poles.


On the other hand, the 13' length is more similar between all brands, everyone is between 13'0 and 13'3 and does 5lb increments.


It's also important to note that the pattern of the pole also influences how stiff it feels. You might have a Spirit, Altius, ESSX, Skypole, and CarbonFX that were all the same length and same stiffness when flexed, but some of the poles may "feel" stiffer to the athlete depending on the style of their jump. Some poles are more forgiving of a bad takeoff, others may unbend a little quicker at top.

Also, most athletes do not perform the same way each jump. If an athlete believes they are jumping on a stiffer pole, they may try too hard and find the pole to be MUCH BIGGER when the real problem is their takeoff fell apart.

[KirkB]

Can someone explain to me why two poles of the same weight can have a different stiffness to it?
Is this even true?

I thought the weight rating of a pole was directly related to its flex rating?

Yes, it's true.

In a nutshell (sorry RG, but your reply was a dissertation! ), the WEIGHT of a pole is an approximation of how stiff it is ... whereas the FLEX of a pole is a more precise measurement of its stiffness. So for each pole of a certain weight and length, there are several flexes. The flexes are just smaller increments than the weights.

When you compare weights and/or flexes, be careful that you're comparing poles of the same length. Poles of different lengths often have different spans (between which the flexes are measured), so comparing the weight or flex of a 15 foot pole to the weight or flex of a 16 foot pole might be like comparing apples to oranges.

Kirk

EDIT: Sorry, I said lbs when I meant to say feet. I fixed it to "a 15 foot pole to the weight or flex of a 16 foot pole".

[sduvinage]

That makes sense now.
Thanks for your help RG and kirk

[vault3rb0y]

As long as you know you are jumping on a safe pole (ie. one that is above your weight), it is better to go by the flex number. For both psychological reasons and precision reasons, the flex will always tell you more about the pole than the weight.

BUT make sure you understand two things when comparing poles using flex:

1.) Longer poles will always have a higher flex number, if they are flexed to the same "weight". Essentially a 16' 160 is stiffer than a 15'6 160 if you hold at the same point. It seems obvious, but if you go by flex numbers the 16' may flex to 22.0cm and the 15'6 may flex to 18.0cm, and if you dont look at weights you could jump on a pole without realizing how big it is.

2.) The stiffness of a pole increases exponentially. If you compare the relative stiffness of 20cm, 19cm, 18cm, 17cm, 16cm, 15cm flexed poles.... the stiffness between the 16cm-15cm poles will FEEL much greater than that of the 20cm-19cm. The physics behind that one isn't terribly complicated, but also isnt worth getting into if this is just a summary.

Be safe!

[Bruce Caldwell]

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Stiffness of a Pole
As a manufacturer let me offer some facts here and get rid of a few misnomers that other pole makers do but not ESSX!
PS thank you Rainbow girl and well said!

As long as you know you are jumping on a safe pole (ie. one that is above your weight), it is better to go by the flex number. For both psychological reasons and precision reasons, the flex will always tell you more about the pole than the weight.

This is true vault3rb0y thank you however please do not get hung up on the difference between a 16.0 and a 15.5 the actual comparison on ESSX is about 2 lbs.
Try to not put so much value on a fl;ex number
The flex number of a 12' 2" PVC plastic tube is the same as 12'-125 lbs test pole but you would not vault with it?

BUT make sure you understand two things when comparing poles using flex:

1.) Longer poles will always have a higher flex number, if they are flexed to the same "weight". Essentially a 16' 160 is stiffer than a 15'6 160 if you hold at the same point. It seems obvious, but if you go by flex numbers the 16' may flex to 22.0cm and the 15'6 may flex to 18.0cm, and if you dont look at weights you could jump on a pole without realizing how big it is.

I suggest you always look at the weight first before jumping then the flex. The flex number means nothing to you unless you note the length, the weight then the flex. Flex just shows a relative stiffness within that weight rating, telling you how much stiffer or softer that pole is to any other poles that length!

2.) The stiffness of a pole increases exponentially. If you compare the relative stiffness of 20cm, 19cm, 18cm, 17cm, 16cm, 15cm flexed poles.... the stiffness between the 16cm-15cm poles will FEEL much greater than that of the 20cm-19cm. The physics behind that one isn't terribly complicated, but also isnt worth getting into if this is just a summary.

vault3rb0y You offer a point I feel is worth diving into thank you for mentioning it!
Other companies may not recognize this info you just presented!
Other's flex their pole with more glass within the span claiming to get a better and more accurate flex? However , my opinion is this is not a true statement as a flex measure of more of the grip of the pole does not give you a more accurate flex especially when that area rarely bends or contributes to the stiffness of the pole's flex!
If one knows that on the ends of the flex scale you get a number that is stiffer or softer between it's flex numbers such as you have sited, then they could build the sail and structure of the pole to provide you with a pole that is not affected by this anomaly!
ESSX poles are built for performance, we make the patterns to get a safe, performing pole. IT is not just a stick of fiberglass rolled on a manderal! Engineering has been performed and tested over the years to provide the vaulter and coach with a fine tuned implement!
We build the pattern to get the weight rating and flex number correlation and we build into the pole the necessary things to give you a smooth jump pole size to pole size and length. No other pole company does that!
Let em give you an example; some other companies uses the sail piece with the small side to lengthen or shorten to provide a stiffer or softer pole! they may cut this pattern from 36" to 56" wider providing a stiffer pole and using 2-3 width of the sail from their standard widths of glass!
We feel this will provide a pole that requires one to adjust their timing as they progress through their pole range to a stiffer pole. this waste season time!
A better method is expensive and much more custom to building a pole such as ESSX does! The sail piece small side stays the same length for each diameter manderal ( which is the mold used to wrap the pole on) and the width of the sail determines the increase or decrease of stiffness to the pole. Thus a pole that is smooth bending the same each time except just a little stiffer like you expect!
(See drawing and photos I am referring to "A" and "B" changed to get a stiffer pole rather than what we do which is smoother only moving the width of "C" to get a stiffer pole!) http://officialessx.com/forum/index.php?s=f448616a05b3d6f2a1cb470482000dc4&showtopic=16&pid=17&st=0&#entry17
It is very difficult for other manufactures with the volume they are running to stop production lines and provide you with such a custom part!
And they buy their glass is slit to a certain width and to cut this down for you to accommodate a better pole would increase their costs and is only done on World Class poles custom made!

You may read more about this as I will post more info in the sales forum!

ESSX