Steve all of them that I know of have sort of a pendelum that can swing in a hard frontal stop.. The vehicle crashes and the device swings 1/2 inch or so and triggers the bags which fill before the occupant moves forward 3 inches..
I am not aware of a Jeeper having his bags go off while offroad.. I am sure it has happened and is possible to happen but I'd suspect the Jeeper involved was happy to have the protection.
Others may have more experiences with bags going off...but since nobody has responded my guess is they don't go off much if at all offroading..
Big Jim <img src="/forums/images/graemlins/pfft.gif" alt="" />