h a l f b a k e r yI like this idea, only I think it should be run by the government.
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So what happens to the car behind which doesn't have this system?. |
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They would just have to increase the gap between each car negating this device, except for perhaps when people pull out of side streets without looking which is what ABS is for , ie it lets you brake and steer round the hazard. |
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//They would just have to increase the gap between each car negating this device |
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What about when a kid runs out in front of you? (and no cars behind) Useful, no? |
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But such zones are usually limited to 30mph , now more so 20mph , giving you ample time to stop, if I can stop with a motorbike in a short distance (pulling a monster of a stoppie) a car with 4 wheels and 800% more grip ought to have less toruble. |
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Unless of course they come out at you so close there is no time to react .... and thus this device also won't work because before you can press the brake pedal you've gone through them. |
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Good in theory, but it is in the practical application that the rubber meets the road, so to speak. Not all road surface conditions will be beneficial. Wet tarmac, for one, springs to mind. |
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How about an explosive spike instead, which embeds itself in the road, stopping the car dead? |
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[lostdog], sure, if enough of the energy/momentum was dissipated perpendicular (either vertically or laterally) to the direction of motion. Like jumping off a cliff, it is not the falling that kills you, it is the sudden stop at the end. |
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Normal theory is that the coefficient of friction is constant and more area in contact with the road is compensated by the reduced pressure of contact. So the friction ought to be the same whether you use a small tyre, big tyre, or a large anchor. However, the coefficient of friction is not constant with a rubber tyre, and is slightly more at lower contact pressure. So bigger contact patches are better. |
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That is until it rains, and the tyre planes over the surface. |
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[lostdog]
It'll probably also total your car.
Besides, who's to say the explosive part
doesn't fail, or that the spike doesn't snap? |
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// bigger contact patches are better |
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But you can bring a vehicle to a stop quicker by keeping the tyres rotating and applying the friction in a conventional brake than you can by locking the wheels*. The suggested brake will always use sliding friction, so the advantage of the larger contact patch will have to be larger than the advantage of using static friction. |
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* on normal road surfaces. |
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As my dad says, scrub brakes are bad news. This will reduce pressure on the wheels that steer the car, which will reduce control. And, as said, it just adds more rubber to the equation, skidding rubber, at that. If it put in a giant spike, or something, that would be different. |
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Srimech, of course. I missed that one. |
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Yeah, I was undecided on this one, but the annos are correct and this is a bad idea and here's why: application will remove the ability to steer and though I don't think it was mentioned, this will alter the CG of the car. If you apply this during a panic stop in a turn, you will probably cause understeer and then cause a bit of roll by moving the lift from the corners to the centerline. |
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Cool idea, but sadly (-). |
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The force of the skid would tend to roll the car. Further if you are navigating a curve when you slam on the brakes (admittedly a bad idea) you want to keep "curving" rather than suddenly assuming a forward skid. The system would fail on wet, gravel, mud, ice, and snow conditions. A vehicle suddenly without a suspension is likely to roll over. |
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/What about conish shaped tyres./ |
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There would be a velocity mismatch at the large diameter end versus the smaller diameter. Results? Tyres wearing away rapidly, accompanied by whisps of acrid smoke, massively increased fuel consumption, and quite possibly much less grip as you are always skidding to some extent (compare coefficients of static versus dynamic friction). |
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