anyone got a ballpark figure? dry road. Force acting at 90 degrees to my direction of travel. My little Corsa has been written off by some guy crashing into the side. He managed to spin it through 360 degrees. Im trying to have a guesstimate of the impact speed .
If you hit a FWD towards the back they'll spin quite easily. You'd also need to know the weight of the other vehicle. Can't the police help? - sorry, silly question. ;-(
Ouch. Get one of those "heat up in a microwave" sausage shaped things, as I suspect you`re going to be sore as hell within 2 days.
I was hit by a HGV in 2001 and still suffer now - leaning my head back to relax is one thing I can`t do any more because the pain kicks in within 5 seconds...
I was off for 6 or 7 weeks IIRC, and seriously couldn`t do a thing - i.e. get dressed for the first 3 weeks or so. If it hadn`t been for internet shopping we would have starved to death.
Key thing is what was the road condition. Downforce on back of a Corsa or other small FWD hatchback can be as little as 0.1g (which is why the inside wheel lifts in fast cornering) so it probably didn't take as much as you might think.
This is the stuff that the police and/or loss adjusters will be dealing with. They have simulation programs for exactly this sort of thing.
IIRC dry rubber on dry _clean_ tarmac is about 1.0 This is consistent with the highway code stopping distances.
If you have access to a Psion series 5MX palmtop computer, there is a free program which may assist you. It is available at:-
I was led to believe that the highway code stopping distances were worse case scenarios based upon old dears reaction times and good old thin crossply tyres.
In practice stopping distances are far shorter.
The MOT test requires just 50% efficiency. That is 0.5G. In practise they usually exceed 100%, ie 1G
Downforce? 0.1g?? And in normal physics this translates to?
Yes. Autocar publish stopping distances for every car they test. And nothing is anywhere near as bad as the HC distances.
About 1g more or less - i.e. unity.
Some cars will o a tad more, but an average low profile radial is in that ballpark.
skinny harder compounds do less - a truck may not make much more than .5 g
Doesn't take much. Not even 30m,ph if the impact is right, because it pretty much can lift the car off teh road anyway.
thanks - a bit more info. Hit by vauxhall Cavalier, just in front of passengers door. University (maths, computerscience & physics) son will do the sums - hes been asking about geometric centres of mass (??). I suspect the effective centre for he mass of the car is cloe to between the drivers seats.
Id like to get a feel for this myself - the insurance companies may just take the path thats easiest for them ( ie I pay).
My Psion died a couple of yeasr ago and hgeyve stopped making them, :-(((
In message , p cooper writes
Won't mean a thing to them unless:
The road was closed to all other traffic as soon as possible. Neither vehicle was moved before examination. All marks and positions of resultant debris were accurately measured and noted. The coefficient of friction of the road surface was determined by testing as soon as possible after the collision.
I doubt that would have happened unless the collision involved a fatality or possibility of life changing injury.
Even then, be prepared for hours of argument between expert witnesses on both sides at court.
Utter gibberish.
Firstly, downforce is an aerodynamic term and very few road cars have any of that. Most generate lift at speed.
If you meant weight distribution then still gibberish. The average FWD car has
55% to 65% weight on the front and 35% to 45% on the rear.Finally, neither weight distribution nor downforce have anything to do with why a FWD car lifts its inside rear wheel during fast cornering. That's to do with the relative roll stiffness front to rear. FWD cars have high rear roll stiffness to keep the front (driving wheels) on the ground in corners. RWD cars have high front roll stiffness to keep the rear (driving wheels) on the ground in corners.
Geometric centre of mass is easily found from the front/rear weight distribution which will be published somewhere for your particular car. Probably about 60/40 to 65/35 front/rear for a FWD car.
Coefficient of friction for an average road car on skinny tyres is about 0.8 in the dry. Best is about 0.95 for state of the art tyres of generous width on a sporty car with good suspension characteristics. The American tirerack site gives lateral G force cornering results for tested tyres which will be a decent approximation to the CoF.
Get all that info and you'll still be wasting your time trying to calculate what will happen to one car hit by another. Small errors in the collision position, lift generated and polar moments of inertia will lead to larger ones in the calculated spin.
Dave is absolutely right. You haven't got a hope of getting anything meaningful. I was involved in the nuclear flask crash test a few years ago, and saw the enormous efforts put in by some extremely sharp people at Ove Arup into predicting the result of a much simpler crash scenario. I also used to have to do calculations on train derailments and collisions - essentially one-dimensional stuff with very simple initial conditions, and it was difficult enough to do much better than order-of-magnitude sums in many cases.
To throw another spanner in: everyone has suggested values for coefficients of limiting friction - but once the tyre starts sliding, that becomes irrelevant, of course.
With all due respect to the University son, maths, comp sci, and physics taken together suggest only a smattering of knowledge about anything very relevant.
Actually its not. Sliding is what locked wheels do, and its as Dave said
- somewhere a tad under 1g.
However the rest is valid. Since cars do not stay with all 4 wheels plonked in the tarmac, and corefficient of friction does not strictly apply to tyres (otherwise why have big fat wide ones rather than small skinny ones?) its all meaningless.
If no one was hurt, its unlikely the police will give a toss anyway, and as far as insurance goes, unless you can provide a clear cut case of t'other parties fault, its knock for knock and bang goes yer no claims.
Its simply too expensive to allocate blame: The insurance companies just look after their own knowing it all comes out in the wash finally.
Indeed.
If a locked wheel provided about a G of grip why would anyone bother with ABS?
Perhaps the main benefit of ABS is near maximum braking but still being able to steer. You can't steer with locked wheels.
Because you can't steer. However 1g is generous on a FWD car as much of the weight transfer overshoots the front of the car (i.e nose dives).
It depends enourmously on the road and the conditions, but for example in a
206 on a damp road one can do a complete 360 spin on the handbrake at only 45mph on tarmac.So it may be the person who hit you was probably doing something in this order if it was wet and he hit in the right place.
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