southpawboston
New member
this time about forward excursion, belt webbing, and LATCH bars.
so, the idea of a LATCH belt or seatbelt stretching during an impact has been brought up before. someone here long ago said something about up to 12" of stretching can occur in a really severe impact, allowing the carseat to move forward several inches.
but stretching is a function of belt length. the longer the belt, the more stretch that can happen, since there is a certain amount of stretching that will happen per unit length of belt. so, if you have 24" of path length between two lower anchors (accounting for all the routing through the carseat), you can expect twice as much stretching compared to if the path length was only 12".
i noticed when i test fitted a BV in my car, and later, my signo, that the path length of webbing between the lower anchor and the LATCH bar was only about 4". since there is a LATCH bar in each side, that's 8" of webbing path length for the whole installation. that means that the amount of stretching that can occur is significantly less than if a normal LATCH belt is used. so this would mean that the carseat would move forward much less in a severe impact.
so how does this affect the whole ride-down hypothesis regarding the belt helping the carseat "ride down" during an impact by abosrbing some crash energy through stretching?
and which is better? to reduce the amount of forward movement of the carseat by having less stretch, or to allow more forward movement in the name of energy absorbtion and decreasing the rate of deceleration by stretching?
and how does rigid LATCH rank in this regard? obviously it allows no forward movement at all, except for some forward rotation since no top tether is used.
and finally, the argument against using LATCH and seatbelt simultaneously, which states that using the two together doesn't allow enough stretch for the ride-down... how you do reconcile that argument with rigid LATCH and also now LATCH bars?
so, the idea of a LATCH belt or seatbelt stretching during an impact has been brought up before. someone here long ago said something about up to 12" of stretching can occur in a really severe impact, allowing the carseat to move forward several inches.
but stretching is a function of belt length. the longer the belt, the more stretch that can happen, since there is a certain amount of stretching that will happen per unit length of belt. so, if you have 24" of path length between two lower anchors (accounting for all the routing through the carseat), you can expect twice as much stretching compared to if the path length was only 12".
i noticed when i test fitted a BV in my car, and later, my signo, that the path length of webbing between the lower anchor and the LATCH bar was only about 4". since there is a LATCH bar in each side, that's 8" of webbing path length for the whole installation. that means that the amount of stretching that can occur is significantly less than if a normal LATCH belt is used. so this would mean that the carseat would move forward much less in a severe impact.
so how does this affect the whole ride-down hypothesis regarding the belt helping the carseat "ride down" during an impact by abosrbing some crash energy through stretching?
and which is better? to reduce the amount of forward movement of the carseat by having less stretch, or to allow more forward movement in the name of energy absorbtion and decreasing the rate of deceleration by stretching?
and how does rigid LATCH rank in this regard? obviously it allows no forward movement at all, except for some forward rotation since no top tether is used.
and finally, the argument against using LATCH and seatbelt simultaneously, which states that using the two together doesn't allow enough stretch for the ride-down... how you do reconcile that argument with rigid LATCH and also now LATCH bars?