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Friday, November 2, 2007

BIG WHEELS









How much does your car weighs? 1 ton? 2 tons?
What if I say your car can weigh as much as 15 tons and as little as 100 grams?
People mistake mass for weight.
The weight is but the multiplication of a mass by a force, a momentum of that force to be more precise.
Gravity is a force that pulls you towards the center of the Earth, inertia is another force that makes you offer resistance to trajectory shifts and so on. On Earth, gravity momentum provides all objects a constant vertical force, which multiplied by our mass, results in our weight.
In space, you have the same mass, but your weight is zero.
But we are not in space
Correct, we are in Earth's atmosphere and subject to Earth gravity.
As I said before, the mass never changes which means our weight is always the same... well, not exactly. If you remember right, I said weight implies an acceleration (or momentum) so, our weight would remain the same if and only if the only force (gravity acceleration) would be the Earth's gravity, but it's not.
Weight... Shifts!
Indeed it shifts. Cutting the chase lets go down to driving.
When you hit the gas the weight of your car "shifts" to the back, the back tires, the back chassis, the car "squats".
If the acceleration is amazingly violent, the front will be so light the front tires may be unable to steer from being almost up in the air. When you hit the brakes the weight shifts forward - on a extremely rough breaking maneuver, your rear gets so light that in that moment a little kid could turn your car over by raising it's tail effortlessly.
That's not all...
The seat belt
The weight not only "shifts" but also increases in the movement direction, you may weigh 77 kilograms in the vertical but you will also weigh in the horizontal...
If you are accompanied by a woman on your side with a seat belt, but that same women is holding a 5 kilogram baby in the arms, in a crash, at the crash momentum, the baby can weigh up to 5000 kilograms or more, now, can any women hold on to 5 tons?
The same goes for heavy sharp objects in your car. An Innocent hydraulic lifter in the trunk may turn into a 50000 kg per inch pressure bullet trespassing all the car in a crash. So, do you still think you drive well?
Ok, that might be, but that's not all. "G's" are not just up in the curves and on them, you have weight shift in multiple directions... on we go.
Braking
Modern electronics have made it easy to brake nicely by stopping tire locking and shifting the brakes balance on all four wheels, so I'm going to assume your car is geared with ABS and some sort of EDB (braking stability control).
I'd say most cars are quite safe to drive beyond limits unthinkable 20 years ago, but braking still needs some issues approach.
While turning, the weight also shifts to the tires in the turn opposite direction, as does suspension, the car "lays down" towards the opposite direction you are turning to, the car's side on the inside of the turn will be amazingly light... a little wind is all it may take to turn it over, and if you have people on the "lay ed" side of the car, their weight increases also, as does the stress on their side.
If you brake while turning hard, the weight will go forward and towards the opposite side of the turn direction, that means most of the "stress" will be on one tire alone, the front one opposite to the side you are turning too, what does this mean?
Control
By knowing where the weight is you can act/react correctly. If your tail starts to shift when you break hard in a turn (curve), all you need is more weight in the back, hence, throttle press or brake release BUT there are more variables to consider...
Power issues
You have certainly seen "burnouts" with rear-traction vehicles where the drive gives way to much power to the rear wheels and the ground surface resistance is not enough for the wheels to grip - once they grip, the squat is so hard the front of the car ceases to exist and you have uncontrollable slides all the way.
I'm only talking weight here, so we are not going yet into traction matters - I'll go into front and rear drives under/overstear/counter-breaking issues later - which only add more forces to the equation.
If you brake very hard, remember that your tail will be light as a feather and if it "slips" you need to get weight into it to control it, hence, hit the gas or release the brakes. Then again, if you hit the gas pedal hard - specially with a lot of horse power - remember the front will be lighter and you may loose turning grip, so all it takes is pressing the brakes gently or relieving the gas pedal slightly for the weight to return to the front tires and you get traction back so you can turn.
If you are turning remember the stress goes to the side of the car opposite to the turn direction, if it threats to "turn over" all you need is to counter the massive weight shift by re balancing the car (ending the turn or turn the opposite way - which means turn into the direction the car's weight is shifting to - this in extreme situations) so that the weight gets back on all tires.
Many professional drivers "cut" the turns with the wheel, thus means they slightly turn/straight/turn/straight the wheel in a "zig-zag'ish" way during the turn to avoid the super-stress on one side of the car and lack of weight on the other, this in very extreme "G"-force conditions.
Also remember that having one more person in the car adds mass to it, not well balanced nor fixed mass, and when accelerating and breaking, the harder you do it, the more that same mass weighs and unbalances the full car weight set leading to strange weight shifts - four people in your car mean a lot more stress on your brakes at violent stops, same goes for violent turns and so on.
This all results in the second most important thing you must achieve when driving (the first is the "Don't" I wrote about in another post): being as smooth as humanly possible, no matter how fast you go, be smooth - the most risk inducing factor is lack of smoothness, be smooth, gen til, a harder maneuver may result in fatal weight shifts, even at low speeds, enough for you to loose control.
With a good traction stability control system - most don't have this yet - your car usually does all this for you when you go nearly over it's dynamic limits.
I think we've grasped the subject, but there's a whole lot more to be said about it.
Stay tuned, drive safe. Article featured at: http://www.alvaromrocha.com/en/2007/10/driving-is-heavy.html
© Alvaro M. Rocha
Alvaro M. Rocha. IT and audio engineer, composer, producer, performer: a professional musician.
He is also a martial arts instructor, skilled driver, agressive (stock)market daytrader and mentor available for pre-selected hire.
That, among other things.
Learn more at: http://www.alvaromrocha.com
Article Source: http://EzineArticles.com/?expert=Alvaro_Rocha

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