The ski industry started adding a "flex" number to their boots a short while ago to help customers compare like boots. Frankly I don' t think it means much other than number given within the same brand by the company making them. That may change over time but currently the methods of testing are not clear across the spectrum of boot makers.
But that doesn't stop the gear geeks like myself from wanting to have some way to measure how stiff or soft a boot's flex is. Sad part is flex has so little to do with how a boot feels or how the boot flex is transferred to the ski.
Stiff boots can be a pain and a handful. Or comfortable and respond instantly to your every command in less than a mil-second. Same can be said for a soft boot if you have the skills to use them well.
Below is some info gleaned from the TGR web site and a couple of links.
Old thread was here. Have PM'ed Tony but he's missing so don't have ability to update the list. I will commit to updating the original post. Looking back this goes to 2007 so has some super old boots but is very useful to leave it in so I've kept as much as possible originalBC boot factory numbers
AT Boot Comparative Flex
The list has been (un-scientifically) compiled by:
a) Posters' input comparing their stiffest AT/Freeride boots' flex (Endorphins, Tornado, Aero Freeride) against their alpine boot. A single alpine boot brand's flex range (in this case, Salomon) makes for better comparability in contrast to mixing flex ranges from Lange, Tecnica or Nordica.
b) Once the stiffest AT/Freeride boots flex ratings have been established, the ratings of the softer AT boots were established down the flex range fine-tuning up or down according to, again, posters' input.
Alpine boots used for comparison
140 - Lange 140 RS
100 - Salomon X-Wave 9
95 - Salomon Gun
90 - Salomon X-Wave
120- Maestrale RS
110- BD Prime
THE LIST (stiffest ---> softest) as of March 10, 2013
130 - Dynafit Vulcan, Tecnica Cochise Pro 130
120 - Scarpa Mobe, Tecnica Cochise Pro 120
115 - K2 Pinnacle 130
110- Dynafit Mercury
105 - Scarpa Maestrale RS, Dynafit Zzero ("Green Machine") CF 4-buckle [2011-12 version with full carbon cuff)
100 - Dynafit TLT6, Tecnica Cochise Light 120, Black Diamond Factor, Dynafit Titan, Titan UL, Scarpa Hurricane
95 - Scarpa Typhoon/Skookum (stiff tongue), Garmont Endorphin, Garmont Axon
90 - Dynafit TLT5 Performance, Dynafit One PX, Black Diamond Quadrant, BD Prime, Garmont Radium, Dynafit ZZeus, Dynafit Aero Freeride (4-buckle)
85 - Scarpa Maestrale, Scarpa Tornado/Pro (black tongue), Dynafit TLT5 Mountain, Scarpa Spirit 4 (black stiffer tongue), Garmont Adrenaline, Dynafit Zzero ("Green Machine") CF 4-buckle [pre 2011-12 version), Black Diamond Method, Salomon Ellipse e2
80 - Scarpa Denali XT/TT, Scarpa Spirit 4 (green softer tongue), Lowa Struktura Rodeo/Pro, Dynafit Zzero PX 4-buckle
75 - Scarpa Rush, Scarpa Spirit 3, Garmont Megaride/G-Ride, Lowa Struktura Evo, Dynafit Aero Speed (3-buckle), Dynafit Zzero CF 3-buckle
70 - Scarpa Matrix, , Old Scarpa Denali (4-buckle red shell), Dynafit TLT 700
60 - Scarpa Laser, Garmont Dynamite, Dynafit TLT 500 (2-buckle + strap), Scarpa F3
50 - Scarpa F1, Garmont Megalite, Dynafit TLT 4 Evo (3-buckle), Dynafit TLT 4 Lite (2-buckle + strap), Dynafit Zzero 2C
This is a work in a continued progress on my part,
and not everyone will agree. Factory published numbers are highlighted.
La Sportiva Spectre 110 /120 flex rating from LS. I think it is stiffer than the Freedom SL and the TLT6 with the black tongue if you buckle it tight. Leave it buckled loose and it is definitely softer than the TLT6 but still very progressive. It is defiantly a different boot than anything else I am currently skiing in.
Freedom SL- Scarpa gives it a 120 flex (softer and more progressive than the Maestrale RS IMO)
Nice plug boot technology with a decent walk mode. Also a full pound heavier per boot than the Spectre.
110+@ TLT6 P w/ black tongue, with the CT liner (could be more yet with a Intuition/Power wrap or another buckle) Still the lightest boot here and one of the stiffest.
110-@ Dynafit Zzero ("Green Machine") CF 4-buckle, the last 2011/2012 full carbon cuff model
105+/- @ Dynafit TLT5 Perf w/black tongue,. buckled in tight with the power strap...damn close if not better than a RS IMO
105 -@ Scarpa Maestrale RS, a lot of boot but IMO not all that stiff in forward flex (Scarpa give it a 120 flex)
90+@ BD Prime (been two seasons now since I was in this boot so I could be way off here) (BD gives it a 110 rate.)
85+ @ Dynafit PDG A stiff and rather short boot. Slightly less tall that a TLT of any generation and a thin/lwt Palau heat moldable liner. Likely able to push a lot more ski than I ever give it credit for.
85 @ Dynafit One PX softer cuff than a TLT Mtn with tongue in place, stiffer sole than a TLT5 (great boot but softer than I remembered..all in a good way though, love this boot)
85- @ Dynafit TLT5 Mountain, stiffer cuff than a One, negated by the hinged sole of the TLT5 platform (another really good boot IMO that doesn't reflect the low number while skiing)