Consisder where the knife has to be mounted in a car and all of the intervening levers, wheels, straps, consoles, etc. that it might hang up on and a large knife becomes less practical because of the mechanics and obsticals of the draw and deployement.
If you don't have a practice knife of the size of the desired knife, take a flat foot long ruler (that's likely to give you between 6 and 7 inches of "blade") and tape it with blue tape anywhere you might consider. Strap yourself in the driver's seat. Roll all the windows down. Turn the radio/stereo up to 11. Jump out of the car and run around it 3 times to get your pulse racing and then race to get back into the seat, slam the door, and strapped in to "draw" the knife. The idea is to simulate the stress and surprise of needing the knife "right now". The longer the blade the more to hang up on all the "clutter" in a car.
If you don't have a practice knife of the size of the desired knife, take a flat foot long ruler (that's likely to give you between 6 and 7 inches of "blade") and tape it with blue tape anywhere you might consider. Strap yourself in the driver's seat. Roll all the windows down. Turn the radio/stereo up to 11. Jump out of the car and run around it 3 times to get your pulse racing and then race to get back into the seat, slam the door, and strapped in to "draw" the knife. The idea is to simulate the stress and surprise of needing the knife "right now". The longer the blade the more to hang up on all the "clutter" in a car.