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Retention / Anti-pre-release

    Alpine ski-bindings are highly engineered products that have evolved significantly at the intersection of — skiing-technique-science, structural-engineering, biomechanics, orthopedics, physiology, epidemiology, axiomatic-design engineering, quality assurance, safety-standards, manufacturing engineering, fatigue analysis, formal field-testing, styling, safety-engineering, and product liability insurance compliance.

    The first and foremost requirement of ski binding function is retention (anti-pre-release) of the boot to the ski — hence, the name, "binding".  A ski binding must bind the ski to the boot.  Failure of this requirement means that the binding is not allowing the skier to ski.

    Retention / anti-pre-release is critical because if a binding pre-releases, the skier will lose skiing-control — potentially impacting another skier, a tree, a lift tower or even firm snow.  These kinds of impacts can lead to head, neck, spine, shoulder — upper body injury.  Blunt loading to the upper body can cause severe injury or worse.

    Skiing control-loads — efforts by the skier to shape their line through the snow — pass from the boot to the ski through the binding.  The desired action of the skis through the snow is dependent upon a proper-transfer of the control-loads that flow from the skier through the binding (please see the 'Edge Control' sub-section herein). 

    Retention / anti-pre-release is supplied by the binding's functional characteristics, not solely by its release setting.  Release settings control the release-function (please see the 'Release' sub-section herein).

    22 American ski-binding companies have gone out of business.  Each binding company has gone out of business largely in-part because each company's bindings could not supply proper 'retention' / anti-pre-release — independently of their release settings.  Think about bindings like Cubco, Burt, Besser and other high pre-release bindings that could not supply retention irrespectively of how high the settings were adjusted.  Those bindings failed to provide basic retention — thus the companies behind them failed.

    The signature of a good binding is one that can be skied at low settings — without pre-release.

    Loads pass from the ski into the boot — in the opposite direction — too.  These loads can be massive in magnitude — sometimes over a thousand pounds in certain directions, though typically lasting only a millisecond or two, and are immediately cancelled by opposing forces that flow through the ski-boot-binding interface ... such as, for example the thousand pound compressive forces that act between the toe-piece and the heel-unit when a ski is flexed and when the forward-pressure mechanism bottoms-out while a long ski-boot and a flexible ski are involved.

    We call skiing control loads, 'steering-loads' (a term roughly translated from the German);  and loads that arise from the skiing environment that enter the ski then pass through the binding-boot-skier — 'disturbing-loads' (also roughly translated from the German).

    Q:  Why not just nail the boot to the ski? 

    A:  Because one must get on and off the skis through the latching and unlatching of the bindings — that's 'convenience';   because bindings should absorb some of the harmful shocks that occur during skiing;   and because the ski must be released from the boot when injury-producing loads arise.  'More on convenience and release is found under their respective sub-headings within this Tech Info section.

    Let's focus on the retention function of ski bindings — in view of the 'competing functions' of convenience and release.

    The nature of the loads that flow through the skier-ski-boot-binding system in both directions — steering and disturbing — are comprised of a simple 6-degree-of-freedom system — 3 rotational loads (pitch, roll, and yaw) and 3 linear loads (fore-and-aft shear, lateral-shear, and vertical shear).  The magnitude of the loads ('loads' = forces, torques, and bending-moments) within any of these 6 degrees-of-freedom — during skiing — can vary from zero to 'significant'. 

                                        —Drawing by Lee M. Berard

    The duration of the loads that pass through this 6 degree-of-freedom system range from a few miliseconds to seconds.  For details, please see U.C. Davis Professor Maury Hull's PhD Thesis on this type of on-snow retention-measurement analysis (1975).  Every binding company relies on on-slope retention loading analysis.

    Much of the on-snow retention loading environment — whether it's steering or disturbing — is a direct result of the skier's ability and experience, as follows:

1—  Yaw (twist) retention loads are low with increasing ability and experience — but an occasional, very high twist load resulting from a spectacular recovery defines the worst case scenario for maximum innocuous twist retention-loading.

2—  Roll (edging) loads increase with increasing ability because an experienced skier knows how to get a ski up on edge.  High edge-control loads are generated when skiing on firm snow — especially with wide and/or shaped skis.

3—  Forward bending loads (forward bending moments) significantly increase with skill because speed is usually associated with skill and experience:  high forward deceleration causing large forward bending moments occur when speed is mixed with bumps, ruts and sudden changes in snow conditions.

4—  Backward bending moments increase with skill because the rear-portion of the ski is sometimes used to finish turns — and skiing steep terrain often induces large backward bending moments.

5—  Lateral shear loads decrease with increasing skill because skilled skiers do not skid turns. 

6—  Vertical shear loads increase with increasing skill — because skill-related speed increases the vertical change in momentum when skiing through compressions.

7—  Forward shear loads can increase with speed ('increase' — as a squared-function of speed ! ).

     (All speed-related loading causes a squared-relationship with disturbing forces;  not so much with steering-forces.)

 

Skier Weight

    A skier's weight directly influences the magnitude of retention-loading, as described by Newton's 2nd equations — even though weight has a far lesser effect than speed (1/2-the-weight-effect).  When heavy skiers experience a change in momentum, large loads can flow through the ski-boot-binding-skier system.

    Load duration is significantly influenced by the 'density and hardness' of the snow.  Icy conditions induce short duration, millisecond impacts — dynamic loading when inertia is significant — whereas longer impulses occurring over a tenth of a second enter the system in soft snow. 

    As long as the skier can fluidly interact with these loading environments, the binding should retain the skis to the boots.

    A mechanical binding's ability to provide retention depends on the key elements of — elasticityrecentering timefriction-reductionboot-to-ski kinematics;  and most importantly — functional-decoupling.

 

Elasticity

    Ski-binding elasticity is defined as the relationship between the the force that partially-separates a ski from a boot, together with the relationship between the remaining 'recentering-force' that pulls the ski back to the boot, strongly and fully to a nearly-centered position (see below). 

    The initial stiffness that separates the ski from the boot — the first 2mm to 3mm of movement — must be 'semi-rigid' to provide ski-control.  However, if the initial-stiffness is too stiff (e.g., 95% of the release-limit is reached at 2mm), excessive stress is transferred to the skier — causing fatigue and joint-pain;   too soft (e.g., 95% of the release-limit is reached at 4mm), skiing control is mushy and ineffective.  Many of today's low-end heel-units are too soft, causing poor edge control.  Today's pin-bindings are far too stiff:  knees can ache after a full day of skiing on hardpacked snow — especially with wide, shaped skis.  This aspect of ski binding function is analogous to the distinctions found when driving with top-of-the-line high-performance tires compared to driving with retreads (see below 'concept' — not actual).

    The total elastic-travel must also have an optimal operating range.  Too little total elastic-travel inhibits retention (the ski can pre-release, sometimes causing serious injury);  too much elastic-travel can delay necessary-release, causing tibia-fracture and/or knee injury.  The typical adult ski-binding elastic operating range is 22mm to 32mm laterally at the toe;  20mm to 40mm vertically at the heel;  and, uniquely to Howell SkiBindings — 15mm to 18mm laterally at the heel.

    The recentering-effortthe work supplied by a binding to pull the ski back to a nearly-centered position with the boot — must be as high as possible.  This 'work-effort' is measured in Joules and cannot be less than an amount that is strictly standardized according to international ski-binding standard ISO 9462.  The 'restoring-effort' directly effects 'recentering-time'.

    Recentering-time is another measure of effective elasticity.  Measured in milli-seconds (ms), a good binding is able to pull a ski back to a nearly-centered position on the boot, quickly.  Sluggish recentering-time invites pre-release.  For example, when skiing on frozen groomer-tracks, a rapid succession of innocuous loads are encountered.  If the binding goes into an elastic-displacement mode, but cannot rapidly recenter the ski to the boot between successive impulses, pre-release will occur — the ski will incrementally 'walk' away from boot until there is a full (and unnecessary) release.  A well-functioning binding (like 'a well-oiled machine') provides fast recentering time independently of high release settings.  'Recentering-time' is functionally connected to the 'restoring-effort' (see above paragraph).

    In summary, elasticity is a key ski-binding function that allows the ski-boot-binding system to resist full-release when encountering large but innocuous skiing-loads.  In high-loading but innocuous situations, elasticity allows a 'partial release' ... until the steering-load or the disturbing-load dissipates. 

    However, ineffective retention (pre-release) can occur even when a binding deploys excellent elasticity — when functional-decoupled is not robustly deployed throughout a binding mechanism (see below).  For example — Spademan ski bindings (out of business) had excellent 'elastic' properties, but pre-released excessively in the absence of greatly elevated release settings.  Single-pivot toe-pieces formerly made by a long-standing French ski-binding company had excellent elasticity, but pre-released excessively in the absence of greatly elevated release settings.  In both cases, the excellent elasticity that was supplied by each binding was incorrectly mechanically cross-linked with other sub-mechanisms that were not functionally-decoupled from the retention function.  In the case of Spademan, each mode of retention (there were many) was adversely cross-linked to other modes of retention:  a large forward bending moment would not only cause forward bending elasticity to become activated, but so also was torsional elasticity forced to become activated — simultaneously.  This simultaneous double duty compromised each mode of retention.  Pre-release was systemic with Spademan irrespectively of the release setting.  In the case of the single-pivot toe-piece, its lateral toe retention-function was cross-linked with ski flex.  Even a small amount of lateral toe-movement during ski-flex caused pre-release — thereby over-stressing the toe-piece's lateral retention-function.  In both cases, excellent elasticity could not compensate for the absence of functional decoupling. 

 

Functional Decoupling.

Only Howell SkiBindings are fully-decoupled between retention and release:

 

Whereas ordinary 2-mode bindings adversely cross-link retention and release:

    The principles of Axiomatic Design Engineering, formalized as the first new engineering discipline in over 100-years by MIT Engineering Professor Nam Suh, are utilized robustly in Howell SkiBindings.  In this way, release is smooth — only when needed, biomechanically.  'And retention / anti-pre-release is powerfully available — always.  Only Howell SkiBindings deploy fully-decoupled Axiomatic Design Engineering technology.  Only Howell SkiBindings deliver powerful anti-pre-release independently of the settings.  Howell SkiBindings are uniquely the 1st bindings that can be skied at 'chart settings' without pre-release.  This is a 1st within the category of alpine ski bindings.

    Almost all ordinary 2-mode ski-bindings today have certain forms of adverse cross-linking (the absence of functional decoupling) that compromise their ability to provide retention independently of the release-function.  Such binding designs cause skiers to crank their settings — thereby compromising necessary release, when needed.  The solution should not involve a band-aid approach that adversely effects the release function.  The right solution is to design a binding that deploys robust functional decoupling, throughout.  Stated in the affirmative:  (1) each mode of retention should be functionally-decoupled from ski flex;  (2) each mode of retention should be functionally-decoupled from the other modes of retention.  In these ways, a good binding can supply powerful retention independently of the need to increase release settings.  Howell SkiBindings are uniquely loaded with robust functional decoupling.  See charts, above.

    Consider this:  when the heel of your ordinary 2-mode binding is stressed so that its heel cup starts to rise, elastically — is the top surface of your boot's heel projection located above or below the heel cup's axis of rotation (above or below the axle that allows heel-cup-movement)? 

    Answer:   During the combination of aggressive forward loading and significant ski flex that occurs during normal skiing, EVERY 2-mode binding's heel unit on market can cause the top surface of every alpine ski-boot's heel projection to become located ABOVE the heel cup axle's point of rotation — thereby forcing the heel to pre-release during forward-loading when the ski is flexed.  This means that each time you experience an innocuous forward load (like aggressively forward-weighting your ski to initiate a sharp turn) when the ski also becomes flexed — the heel unit is automatically being forced to open ... when, in fact, there is no need for your heel to release.  Today, one addresses this situation by pre-selecting elevated heel settings.  With Howell SkiBindings, the heel cup's axle is built-into an elevated position so that the combination of forward loading and ski flex does not effect forward heel retention.  This form of functional-decoupling negates the need for elevated heel settings.  Howell SkiBindings deploy decoupling technology in all 3 modes of retention.

    Howell SkiBindings have built-in functional-decoupling so that they can be skied, aggressively, in all conditions without the need for cranked-up settings.  By this approach, the release-function is not compromised in order to gain proper retention and anti-pre-release.  Functional decoupling provides this major benefit.  With Howell SkiBindings you can uniquely have it both ways — powerful retention AND necessary release, without compromising one function for the other.

 

Friction Reduction

    A binding's inherent level of friction — its 'internal friction' within its inner-workings and its 'external friction' between the binding's interface-surfaces with the boot — is a sub-function of the elastic retention function.  Friction adversely effects elasticity.  When encountering innocuous disturbing loads, the less the internal and external friction of a binding, the better a binding can return the ski to the boot, efficiently and independently of the release settings.  Imagine a 'slinky' spring being connected to a wall at one end, then stretched across a carpeted floor, then released.  Then imagine the same slinky-spring being stretched on a smooth polymer floor, then released.  On the high-friction carpeted floor, the slinky will move slowly and may not return to its original, unstretched, position.  Reducing friction at the sliding interface, as with the smooth polymer floor — the slinky will return to its original unstretched position, fast and completely.  This example applies to ski-bindings in each mode of retention — 'each mode' being lateral at the toe, vertical at the heel, and in the case of Howell SkiBindings, laterally at the heel.  Reducing friction through the use of low-friction materials within the inner-workings of the binding mechanism and reducing friction at the external boot-interfaces — contributes to powerful, fast, and complete retention, independently of the release settings.  A ski binding must maintain low friction within its inner-workings and externally at all boot interfaces.  Howell SkiBindings make large and significant use of knuckle-joints to minimize internal friction.  Externally, Howell SkiBindings maximize the use of pure, thick, DuPont Teflon interfaces.  Teflon is the only substance that maintains a low coefficient of friction even when contaminated with dirt, sand and salt (mechanical AFD's can seize-up when contaminated even with one small piece of sand).

    Again, however, no amount of friction-reduction can overcome a lack of functional decoupling.  A good ski-binding must be maximally decoupled, functionally, in order for low-friction ski-binding operation to be effective.

 

Boot-to-ski kinematics

    The path that a boot moves-through (its kinematics) during elastic-retention is closely associated with its decoupling function.  For example, if a boot is moving laterally during elastic toe retention and it is also forced by the binding's kinematics to move slightly forward — the binding will have tremendous difficulty pulling the boot back to its originally centered-position on the ski while the skier unexpectedly encounters a pile of warm slushy snow:  the sticky-snow will decelerate the skier — generating a large forward-shear load from the boot into the toe-piece of the binding.  If this situation also involves innocuous lateral loading — the combination of the innocuous forward-shear load plus the innocuous lateral load will result in pre-release ... if the binding allows the boot to undergo lateral elastic movement that also includes forward movement (single pivot ski-bindings cause this kinematic path).  In all cases during lateral elastic movement in skiing, the boot must have a purely-lateral kinematic path of motion — guided, controlled, and shaped by the specific kinematic function of the binding.

    A good ski-binding controls the desired kinematics of the boot relative to the position of the ski during elastic retention — in each mode of retention — laterally at the toe, vertically at the heel and laterally at the heel. 

    Further, a good binding's kinematic control of the boot's path of elastic-motion in one mode of retention should not cause adverse kinematics to develop in the other modes of retention.  Kinematic-decoupling plays a critically-important role in supplying retention and anti-pre-release.

 

Independent adjustment of each mode of retention

    Ski bindings that deploy independent adjustment of each mode of elastic-retention further satisfies the functional decoupling axiom.  The Geze SE3 ski binding that was successfully sold between 1981 and 1984 provides a clear example.  The Geze SE3's lateral toe retention function operated fully-independently of its vertical toe retention function.   Each mode of retention — lateral and vertical — operated fully-independently of the other.  In this way, each mode of retention could supply maximum retention — elastically, frictionally, stiffness-wise, recentering-wise, kinematically — completely and independently of how the other modes of retention were functioning.  If, for example, friction somehow became added to one mode of retention — the other mode was unaffected.  Stress to one mode had no effect on the other mode.  Disturbing loads that enter the ski in one direction — actuating the retention-action of one mode — have no effect on the retention-action of the binding in the other modes of retention.

    In an importantly inverse way, it is imperative that a binding's retention functions do not cross-link with its release-functions, too.  More, on release in the other sub-tech-section.

 

Dynamic retention

    The human musculoskeletal system responds differently — visco-elastically — to the introduction of slow loads that effect retention — as compared with fast loads that effect retention.  Even slow loads 'move' — so we call slow-loading 'quasi-static loading'.  Loads where the mass of the object that's being impacted 'significantly resist' the applied load (due to inertia) are called 'dynamic loads'. 

    Bindings also behave differently when subjected to quasi-static loading as compared to dynamic loading.  This difference between quasi-static ski-binding behavior and dynamic ski-binding behavior is mostly attributed to the differences between the 'starting-friction-properties' and the 'moving-friction-properties' of the various materials that slide against each other, internally and externally, during ski-binding retention-function.

    International ISO standard 9465 (despite its title-misnomer) measures lateral retention during dynamic loading.  Rick Howell is a principle co-author of this standard.

    Rick Howell — the founder of Howell SkiBindings company — has, over the past 45-years, developed proprietary and significantly advanced dynamic-impact laboratory-testing equipment to measure lateral toe-piece, vertical heel-unit, and lateral heel-unit — retention function.  These proprietary variations of ISO 9465 mimic on-slope dynamic retention behavior in terms of a comparative rank-order retention-function with previously known on-slope ski binding retention behavior. 

    Expressly because of this extensive background, Howell SkiBindings out-perform even the newest competitors' bindings that have active damping — in dynamic toe-piece function (laterally) — see graph, below.

 

    Further, Howell SkiBindings out-perform all other heel-units in forward retention — see graph, below;  red-line.

 

Dynamic forward-impact:  Pendulum length:  450 cm;  Pendulum mass = 11 kg;  Static preload = 4 kg;  Impact at 95cm forward of projected-axis-of-tibia;  Impact angle = 34°;  ISO 9838 Test Sole.  Red-line 'A' = Howell 888 Max.  Howell 888 Max set at 8 DIN in the heel = the same level of retention as other ordinary 2-mode bindings set between 12 DIN (lite blue line) and 18 DIN (orange line).

 

    These achievements are due to the ski-binding operating experience of Rick Howell (see 'About Us' in the Menu) — and based on tens of thousands of ski-binding development tests in the lab and especially on-snow over the past 45-years.

 

On-slope retention

    All of the above lab-based standardized test methods are important and 'ok' — but they are not especially difficult to pass — and they are not performed on-snow.  The real test is on-snow.  However, on-slope testing for retention is dangerous.  Each binding company has developed proprietary methods to conduct controlled on-slope testing for retention. 

    Howell SkiBindings company is located in Stowe, Vermont USA where we test ski binding retention, on-slope, at Stowe Mountain Resort under wide-ranging snow and terrain conditions over seasons of aggressive skiing.  On-slope testing is performed ONLY AFTER a given new binding design passes all of the 'pre-tests' for the main international ski binding standards (ISO 9462, 9465 and 11087) — and ONLY AFTER the same binding performs well in the proprietary lab testing for retention.  Bindings become commercialized ONLY AFTER all of the above testing has taken place — PLUS only after a full season of on-slope testing by a closed group of known test-skiers.  These final steps are taken very seriously.  Rigorous on-slope testing is crucial to developing superior ski-binding performance.

 

Standards specifically for ski binding retention

    International ISO standards that measure retention and anti-pre-release are in-place for lateral toe retention.  There are several retention 'provisions' that quantify the effectiveness of toe-piece retention within ISO standard 9462 and ISO 9465.  There is a 'loose non-quantitative provision' within ISO 9462 for on-slope heel-piece retention function. 

    Published, non-standardized test methods exist to measure the quasi-static retention of heel-piece function — are described by a university in Munich.  However, there are no published test methods, nationally or internationally, that measure dynamic heel-piece retention.  See graph, below, for Howell SkiBindings quasi-static forward heel retention test:

 

    Howell SkiBindings company has — over the past 45-years — developed in-house test methods to measure dynamic heel retention.  This is important because most ordinary ski-bindings pre-release at the heel.  Howell SkiBindings company also has developed proprietary lab test methods and proprietary on-slope test methods to measure each mode of retention:  lateral at the toe, vertical at the toe, vertical at the heel, and lateral at the heel — that exceed the requirements of the international retention standards.  For more information about Howell SkiBindings unique and advanced in-house anti-pre-release test methods, please contact

         Howell SkiBindings 
         < rick.howell@howellskibindings.com >

 

Verification of the retention-function

    At the end of the day, a ski-binding's retention-function is accessed by how low the release can be set in each mode of retention without causing pre-release.   The signature of a good binding is one that can have its release adjustments set at (or below) 'chart-recommended-settings' — without pre-release.   Each binding design has a unique retention-signature based on how robustly all of the above functions are deployed, tested and refined. 

 

Conclusion:  ski-binding retention / anti-pre-release

    Unlike the release function of a ski binding that can be adjusted by a ski shop and/or by a skier — the critical retention function is controlled solely the functional characteristics that are uniquely designed and permanently built-into each binding, model by model, brand by brand.  The retention-function of a given binding design is determined by the specific binding-design, independently of the release settings.  Poor binding function requires high release settings to maintain retention — but then, necessary-release is sacrificed.  Good binding function — as described above — provides powerful retention / powerful anti-pre-release at non-elevated release settings. 

    Binding companies that say "release/retention" settings in their literature provide bindings that must have elevated release settings to provide good retention  ( BTW — that's all of the other binding companies ).

    We trust this essay helps you identify the features and the functions of ski-binding design that provide powerful retention without the need for elevated settings.

 

To Order by Reservation-Deposit, now:

Howell 800 Venus — Loaded with ACL-Friendly features for women.  DIN 2.5-9

Howell 880 Pro — High DIN's plus ACL Friendly skiing — without pre-release.  DIN 5-15

Howell 888 Max — CAUTION: FOR EXTREME SKIERS AND RACERS, ONLY.  DIN 6—18 

See prices—including low $80 Reservation Deposit—in the on-line catalog.



 

  Anti-pre-release. ACL-friendly.
FLAT-OUT SKIING CONFIDENCE.

          Howell SkiBindings
            It was inevitable.

 

 

79A Mansfield View Road   •   PO Box 1274    •   Stowe, Vermont 05672  USA
1.802.793.4849  •  rick.howell@howellskibindings.com  •  www.howellskibindings.com