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High collision bumper/anchor

Heavy solid bumper takes head on rear collision and drops to stop car
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Ok, i've always known the more friction area you have the better the stopping power right? well imagine a 400lb concrete bumper with a 2 inch thick rubber bottom that hydraulically slams down to the pavement like a huge tire and grinds the car to a halt in emergencies. essentially its like tripling your tire surface area. and its heavy enough to dig into snow and mud like an anchor.
Arcanus, Mar 11 2010


       Know what else would make the car stop faster? Not adding 400lbs.   

       The thought of losing any sense of control that the ABS is providing during this moment is not very comforting.
AutoMcDonough, Mar 11 2010

       alternately you could have most vehicles equipped with an air bag suspension that drops the car on the ground thus making a HUGE drag area.
Arcanus, Mar 11 2010

       I like Arcanus's version better. But in that case you are effectively removing the suspension, the car could bounce like an empty dump truck and you are worse off than just letting the front tires do thier thing.
AutoMcDonough, Mar 11 2010

       Completely counterproductive: Dropped to the ground, the anchor continues forward under its own momentum. Its static friction is considerably less effective than the tyres' braking capability. Essentially, the anchor would be dragging the vehicle forward. For better brakes, lower the centre of gravity, improve the brakes, tyres, and suspension.
sstvp, Mar 12 2010

       is it too late to invent an anchor that fires into the ground with a big thick bunjee cord out the back?
Arcanus, Mar 12 2010

       lol @ the thought of getting rear-ended by a stopped car.   

       I've thought of firing anchors into the ground before, but that was more of an anti-towing prank. edit: now posted up for seperate discussion not to derail this one
AutoMcDonough, Mar 12 2010

       Arcanus - it's too late to invent the harpoon brake you outline on Mar12 there, but not too late to be the first to build one. NHTSA played with the idea in the lat 70s and gave up. Mercedes have shown a protype airbag that inflates under the front of a car as an auxiliary brake, but it only fires once at about $500 a pop.
sstvp, Mar 12 2010

       Why not go with the 400lb concrete bumper, but make it snowplough-shaped and do away with the braking concept entirely? Trains are seldom seriously damaged by collisions with cars.
MaxwellBuchanan, Mar 14 2010

       //Ok, i've always known the more friction area you have the better the stopping power right?//   

       Unfortunately, it's wrong regardless of how long you've known it.   

       Drag force = coefficient of friction(dynamic) x normal force applied to surface   

       Area doesn't enter the equation. It can have an effect on heat dissipation, so if the materials in your tires or brakes change properties as the temperature goes up, that can be a problem; but it's a different problem.
lurch, Mar 14 2010

       Well, strictly speaking, in classical physics area does not effect friction, but depending on what materials you use, other forces can come into play which do make area matter. Adhesion, primarily--the "stickiness" of the material in question, which for rubber is very non-trivial.   

       This is why race cars and dragsters use big fat slick tires--according to the ideal laws of friction tire size shouldn't matter, but in the real world, it does.
5th Earth, Mar 14 2010

       Well, racing conditions aren't very real-world. The other way of looking at the purpose of wide tyres is that they dissipate load across a broader area, and thereby allow a tyre surface to be made of softer, grippier compound. Some would say the grip better because they're more expensive, and the width is there to give durability to the soft compound. But then there's that problem of a narrow contact patch being necessary to break through a coating of rain/snow/debris, that isn't really an issue on a drag strip or track. Fundamental way to improve grip: spend money on it. Grippier tyres, with shorter tread life, will definitely achieve this - like the autocross tyres you can buy for street cars.
sstvp, Mar 15 2010


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