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# Flex Index of Boots

I'm just curious... how is flex index of boots measured, and what are the units?
The measurement and units vary from company to company.

Like Salomons with a 100 flex index are considered stiff recreational boots and I beleive that Atomics rated at 10 are similar.
Quote:
 Originally posted by Scalce:The measurement and units vary from company to company. Like Salomons with a 100 flex index are considered stiff recreational boots and I beleive that Atomics rated at 10 are similar.
It is, however, somewhat likely that the number printed is related to the actual bending moment of the boot as measured in metric units, i.e. Newton*meters. 100Nm is a fairly stiff boot. Since 10Nm corresponds to about 7 ftlbs, which you can generate with your hand when tightening a fastener, I am tempted to believe that Atomic either divides its measured flex numbers by 10 or thereabouts or they use some sort of "apparent feel" subjective scale.

The other assumption, of course, is that the flex index is a constant independent of the actual flex angle. In the manner of such things, it is probably accurate for small angles.
the other fun thing about boot flex ratings is they are not constant like for instance binding DIN. The flex rating are generally set by the individual companies based on an index boot. Meaning that the ejc 1000 would be given a flex rating of 100 and then the softer boots like the ejc 800 or ejc 600, 80 and 60 respectively. Stiffer boots than the 1000 in the line like teh ejc race would get a rating of 110 or higher to entice the poor schmo who still feels the need for race boots.
Another thing to consider is that the boots are all rated for forward flex not lateral which is where a modern ski is turned from. So for example a rossi soft is actually more stiff laterally than the see through green Sally 4 buckle boot but it has a relatively softer flex rating?
Quote:
 Originally posted by ejc:the other fun thing about boot flex ratings is they are not constant like for instance binding DIN. The flex rating are generally set by the individual companies based on an index boot. Meaning that the ejc 1000 would be given a flex rating of 100 and then the softer boots like the ejc 800 or ejc 600, 80 and 60 respectively. Stiffer boots than the 1000 in the line like teh ejc race would get a rating of 110 or higher to entice the poor schmo who still feels the need for race boots.
[img]graemlins/thumbsup.gif[/img] ejc: race come with flames? [img]tongue.gif[/img] Seriously, I seem to remember Nordica and Salomon with a possibly arbitrary Nm figure printed on there, but you're spot on about the marketing angle.

Quote:
 Another thing to consider is that the boots are all rated for forward flex not lateral which is where a modern ski is turned from. So for example a rossi soft is actually more stiff laterally than the see through green Sally 4 buckle boot but it has a relatively softer flex rating?
Besides, it was probably tested by a lab tech in a white frock coat at 19 degrees C anyway, so it's all just advertising rot.
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