sortaOT: skid marks (cars)

not much metalworking, my apologies.. but i know there
are quite a few (car) knowledgeable people here.
just curious, how fast would a small car (2500lbs?)
have to be going to leave 60' long skid marks on dry asphault?
wife at stake,
-tony
Reply to
tony
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Don't know, but Google is your friend:-
Note that some of the below instructions involve measurements of coefficient of friction and note the method of measuring skid marks.
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(alter the CHXX on the above for different chapters)
Good luck.
Best regards, Spehro Pefhany
Reply to
Spehro Pefhany
wow. thanks for the (great) quick reply. very informative. i am surprised to find that vehicle weight doesnt seem to enter into this.
thanks again -tony
Reply to
tony
No way to compute it. If you brake hard enough to lock the wheels, the cops have tables to determine speed, depending on road surface conditions. If only one wheel is locked or braking hard enough to leave a mark, it is harder to do. If it was spinning wheels from engine power, it is totally unknown unless you repeat it with a radar speed detector. Some cars just barely leave a mark, and almost all energy goes into accelerating the car - they get up to speed fast. And, some cars with light weight on the driving wheels just burn rubber, transmitting very little energy to the car at all.
If you were braking hard, 60 feet sounds like 20-30 MPH, but others can probably answer more accurately.
Jon
Reply to
Jon Elson
On Mon, 08 Dec 2003 21:28:52 GMT, "tony" brought forth from the murky depths:
0-30mph or so, depending upon tranny, tire width, torque, and HP.
Oh, you meant STOPPING speed, didn't you?
2-wheel disc or 4-wheel drum brakes? Bald P155x13" import rubber or on new hi-performance 16" Pirellis? Smooth or coarse asphalt? Hot or cold weather? Warm or cold tires?
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Untie her. That's illegal in most states.
The answer is: aproximately 35mph.
P.S: The disc/drum question is a moot point in a silly skid. If one can how to use the brakes _properly_, discs can help stop the vehicle a whole lot sooner under a whole lot of different conditions.
-- Sex is Evil, Evil is Sin, Sin is Forgiven. Gee, ain't religion GREAT? ---------------------------------------------
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Sin-free Website Design
Reply to
Larry Jaques
I get about 38 mph assuming a coef of friction of .8
physics are phun!
Larry
Reply to
Lawrence L'Hote
On Tue, 09 Dec 2003 00:57:55 GMT, "Lawrence L'Hote" brought forth from the murky depths:
I used the google-provided formula of double the square root of 5 times the length of skid which gave me 34.64 rounded to 35.
Was that cof figure for worn imports or new Pirellis? Laden or unladen?
-- Sex is Evil, Evil is Sin, Sin is Forgiven. Gee, ain't religion GREAT? ---------------------------------------------
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Sin-free Website Design
Reply to
Larry Jaques
you have too many factors to figure out when doing this.. i dont have the paper work anymore on it, but when auto fatalies are involved and there is a real reason to know how fast the car was going that left those skid marks.. the would do a test of the friction on the road.. it was done with a homemade instrument( a half of tire with a lead weight(about the size of a foot ball in the bottom of it and there was a cheap spring loaded scale (like the kinds that they used in the hardware stores when buying nails by the pound... the tire was pulled a few feet in different directions over the road and then scale was read out and then it was averaged for the road... the there was a formula for taking the friction/coeficient of this and then doing something else with it and then the weight of the vehicle and then the possible moisture on the road..... etc.... there is too many factors to just look at tire marks and say that driver was going 40,50,60,70 miles per hour..... but the police can do it with the formulas/and work it out....
Reply to
jim
Cops don't use formulas. Police in my state used to use
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similar but, now, with abs brakes and etc skid marks aren't always present(or much help) in establishing speed in an accident.
Larry
Reply to
Lawrence L'Hote

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