Originally Posted by Jeff Campbell
In the previous study, AFDs were damaged in 43% of AT boot-alpine binding
combinations. Every binding model with a mechanical AFD was damaged; one static AFD, out
of five, was damaged (Figure 3.9). Bindings with mechanical AFDs ranked as the lowest
performing bindings with AT boots (Table 3.7).
Alpine bindings with AT boots were predicted to be 50% less sensitive to changes in
indicator settings than with alpine boots. A significant linear regression model found (F(1, 4) =
40.0, p = .003) that accounted for approximately 90% of the variation in release torque as a
function of indicator settings for AT boots in alpine bindings with static AFDs (R 2 = .909,
Adjusted R 2 = .886, Figure 3.10). Other boot-binding described above often caused AT boots in
alpine bindings with static AFDs to release at higher torque values than allowed by international
standards; however, changes in indicator settings resulted in the same proportional changes in
release torque between AT boots in alpine bindings with static AFDs as alpine boots in alpine
bindings.
In contrast to static AFDs, AT boots used in alpine bindings with mechanical AFDs alter
release characteristics so severely that a linear regression analysis shows that indicator settings
are not correlated with the release torque in anyway (F(1, 10) = 1.43, p = .26, R 2 = .125,
Adjusted R 2 = .037); release torques corresponding to the minimum, median, and maximum
indicator settings often fell within ±3% (Figure 3.10). The three lowest performing bindings
with AT boots incorporated mechanical AFDs (Table 3.7).
The worst load case for mechanical AFDs occurs in Front Preload Twist releases, when a
preload is applied to the fore-body of the ski significantly increasing the pressure between the
soft AT boot sole and AFD. As a lateral load is applied to the ski, softer AT boot soles stick to
mechanical AFD as the binding moves away. During this phase, the spring-loaded cam in the toe
piece, which normally controls release torque, is overcome. Here the boot settles into a local
minima 5-10° past the point when an Alpine boot would have released (Figure 3.10). Internal
friction retains the boot in the ski and the boot must overcome a second energy barrier to finally
release. This final energy barrier is simply a function of the internal friction of the system and is
no longer controlled by the spring-loaded cam intended to control the release torque.
