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Old 2nd April 2007, 19:02   #16
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Originally Posted by rishibravo View Post
I disagree with you that you will experience the low pressure between the vehicles only at the time you are crossing. When a large vehicle like a truck moves it dislocates a lot of air and as it moves forward the air around it will tend to fill the gap thus extending the l low pressure area to some distance away from the vehicle as well. The drag currents ( you can call it turbulance ) are maximum just behind the large vehicle. I dont know if there is any mod which you can do to prevent this but you can try to avoid the are just behind the truck for a few meters.
Usually when we are moving fast on a single lane carriage way we tend to come to the middle of the road as soon as the vehicle coming from the opposite direction passes by. one can avoid the effect of pressure by avoiding coming to the area which was earlier occupied by the large vehicle.

just trying to apply a lil college physics
yup...that sounds about right.

its for the same reason that take offs on runways are time-separated based on the aircraft that just took off. as also the take off pattern of that particular airline. Some airlines go sling-shot, which leaves a lot of turbulence for the next aircraft in line. Some do a gradual ascent.
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Old 2nd April 2007, 20:21   #17
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Can U elaborate ur theory with proof,rishibravo?
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Old 3rd April 2007, 08:21   #18
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Originally Posted by rishibravo View Post
This has nothing to do with turbulance. What happens when two vehicles pass opposite to each other is there is a low pressure built up between the two vehicles (an extension to bernaullis theorem ) and both the vehicles tend to move towards each other. For the same reason two ships never cross each other when they are too close. This is the same reason why you shouldnt sand near the edge of the platform when a speedy tain is approaching or passing by.
So putting a spoiler wont help. Having better traction on the road will definitely help but this pressure phenomenon will always be there.
rishi, turbulent flow is the cause of all this. In fluid Dynamics there are some terms like turbulent flow, Vortex dynamics etc. Now any moving object at a high speed displaces air randomly which causes turbulence (Reynolds No. > 2000 (approx)).
Turbulence gives rise to Vortex (significant at very high speed like airplanes), kind of spiral motion with closed streamlines...
Hence when 2 moving objects pass by, the above factors help to move close to each other. Since cars / trucks are comparatively at lower speeds and a better aerodynamics this attraction is nullified. You can ofcourse realize a little abt this phenomenon if u drive at say 120kmph with wondows rolled down and another fast moving object pass by u...

Present day cars are all designed to counter all this forces way above the limit with adequate factor of safety...

Little what I remember from Fluid Dynamics course from college....
Abhi
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Old 3rd April 2007, 09:25   #19
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@ rishi - I could be a bit off, but I really believe that the low pressure caused while the two vehicles are passing each other, does not cause the car to shake. More so, I think the low pressure that is caused behind a moving vehicle, which in turn leads to eddy currents being formed, hence causing turbulence.
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Old 3rd April 2007, 09:26   #20
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Quote:
Originally Posted by nitrous View Post
Can U elaborate ur theory with proof,rishibravo?

@ Nitrous - as the air flows above the vehicle and below it, there is a low pressure formed just behind the vehicle, this low pressure is the cause for the car being "unstable" at high speeds (nothing to do with the palio). Now the eddy currents are caused by the two streams mixing behind the car, and hence, if you tailgate a vehicle, you do feel a bit of turbulence just behind them, but the further you drop back, the less turbulence you feel. Thats where spoilers come in. a well designed spoiler, streamlines the flow of air, to a point further away, hence the turbulence is moved away from the vehicle, thereby making it more stable. - proof would be watching a rally car on a dirt track, the flow of the mud will show you the dynamics of air flow.

Last edited by madan80 : 3rd April 2007 at 09:27.
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Old 3rd April 2007, 09:29   #21
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Originally Posted by k36 View Post
I can read your mind .. you want spoilers. Then go for it... just don't expect it to help you in the situation described.
Yes, want to get spoilers, but effective spoilers. is it that difficult to design these things?

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And would you really like to design it? How will you test its efficiency? Hope you don't come back and tell me that you have a wind tunnel at home.
Well, dont got a wind tunnel at home, but i can always take it to the same place and see if has the same effect.
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Old 3rd April 2007, 09:30   #22
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Quote:
Originally Posted by nitrous View Post
Can U elaborate ur theory with proof,rishibravo?
you want me to elaborate the Bernaulli's equation?

Bernoulli's Theorem
How pressure and velocity interact
static pressure + dynamic pressure = total pressure = constant
static pressure + 1/2 x density x velocity2 = total pressure = constant
General Concept:
The Bernoulli effect is simply a result of the conservation of energy. The work done on a fluid (a fluid is a liquid or a gas), the pressure times the volume, is equal to the change in kinetic energy of the fluid.

General Facts:
Where there is slow flow in a fluid, you will find increased pressure.
Where there is increased flow in a fluid, you will find decreased pressure.


You can get the test this by holding two strips of paper together and blow in between them and you will see that the two strips of paper will come closer to each other. This is the same phenomenon which happens when a bus or truck passes by you at high speed. This effect is prolonged because in the case under consideration the objects themselves are moiving at high speed.

To elaborate the place where the turbulance is maximum when a vehicle moves please check this link out
They have also mentioned a scoop method to reduce the drag at the rear of the vehicle but in our case (i think) the vehicle coming from opposite direction should be equipped with this .
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Old 3rd April 2007, 14:55   #23
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@ Rishi - it seems to be a rather interesting site.
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Old 3rd April 2007, 15:04   #24
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Originally Posted by nitrous View Post
Get those 185/60/R14 (a la 5u3zer0) or 175/70/R13 michelins and U'll feel more secure.
Both of which are the incorrect upsize for a Palio.
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Old 3rd April 2007, 18:37   #25
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Both of which are the incorrect upsize for a Palio.
But, I was recommeded 185/60 R-14 by a lot of Bhpians. I remember there was a thread for correct tyre upsize for palio and this profile was recommended
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Old 3rd April 2007, 18:43   #26
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Originally Posted by rishibravo View Post
But, I was recommeded 185/60 R-14 by a lot of Bhpians. I remember there was a thread for correct tyre upsize for palio and this profile was recommended
Correct size is 195/60-14 ...
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Old 3rd April 2007, 18:56   #27
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Originally Posted by kpzen View Post
Correct size is 195/60-14 ...
just wordering how did you come to this size. can you please explain?
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Old 3rd April 2007, 18:56   #28
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185/60/R14 is a recommended upsize in the Bridgestone site for Fiat Palio 1.6
Bridgestone India Private Limited

An known friend of mine had upgraded from stock tubes to 185/60/R14. The car is rock solid and the ride is good.
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Old 4th April 2007, 03:56   #29
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Originally Posted by madan80 View Post
the biggest bone of contention was every time a bus passed me in the opposite direction, my car shook like an old mans tooth.

my question is this, is there anything that can be done
the easiest way to cut turbulence is to keep to the left middle of your side of the road on a single carriageway.you increase the distance between your line of motion and the line of motion of the oncoming traffic.
the only other way to make sure your vehicle doesn't shake when a bus passes you by is to drive another bus.
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Old 4th April 2007, 06:29   #30
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Quote:
Originally Posted by madan80
my car shook like an old mans tooth.
That's an interesting description. And how exactly it would be if it's an Omni?
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