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 .

In article ,
p cooper wrote:
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. ;-(

--
*With her marriage she got a new name and a dress.*

Dave Plowman London SW
To e-mail, change noise into sound.

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 .

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.

--
Please add "[newsgroup]" in the subject of any personal replies via email
--- My new email address has "ngspamtrap" & @btinternet.com in it ;-) ---

"p cooper" wrote in message
. ..
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 .

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.

Mike wrote:

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.

Downforce? 0.1g?? And in normal physics this translates to?


--
Grunff

Mike wrote:

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.

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.
--
Dave Baker - Puma Race Engines (www.pumaracing.co.uk)

"Dave Baker" wrote in message
...
Mike wrote:

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.

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.

Downforce is the force acting downwards on the mass of the car. It could be
aerodynamic for a racing or performance car but in this case is just due to
gravity. Although there is 35% of the weight of a FWD though the back when
stationary, this drops to as low as 10% under dynamic conditions such as
heavy braking which is where ny 0.1g comes from. Do you understand now ?



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.

I presume your pumas don't race too well then. A FWD lifts it's rear inside
wheel because the front outside is heavily loaded by cornering forces and
you get suspension compression. On a road car driven fast this is far in
excess of how fast the rear suspension can compensate as this is often
constrained by either a rear anti-roll system or some form of dead axle
connection and the wheel simply lifts. But if you can reduce forward weight
transfer under heavy cornering then the effect is reduced considerably - the
Focus RS is a prime example of how to do this correctly.

As for RWDs the high front roll stiffness is to keep both front wheels on
the ground during braking. Adjusted properly, squat is eliminated and
braking is optimal. It has no effect on the driven rear wheels in corners -
even on an old Mk2 Escort ! For a fully independent rear suspension the
position of the front wheels is nowadays almost irrelevant until you reach
the front suspension travel end point - which for a rally car is enormous
but for an F1 a few cm.

The message
from "Mike" contains these words:

Downforce is the force acting downwards on the mass of the car. It could be
aerodynamic for a racing or performance car but in this case is just due to
gravity. Although there is 35% of the weight of a FWD though the back when
stationary, this drops to as low as 10% under dynamic conditions such as
heavy braking which is where ny 0.1g comes from. Do you understand now ?

Still gibberish though. Last time I looked g was still the acceleration
due to gravity and very definitely not measured in units of either force
or mass.

--
Roger

Mike wrote:
As for RWDs the high front roll stiffness is to keep both front
wheels on
the ground during braking.

What on earth does roll stiffness have to do with braking? There is no
roll under braking.

On Thu, 30 Dec 2004 17:18:55 +0000, p cooper wrote:

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 .

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.



--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html

"Ed Sirett" wrote in message
news
On Thu, 30 Dec 2004 17:18:55 +0000, p cooper wrote:

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 .

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.



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

In article ,
Fred wrote:
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.

Yes. Autocar publish stopping distances for every car they test. And
nothing is anywhere near as bad as the HC distances.

--
*Xerox and Wurlitzer will merge to market reproductive organs.

Dave Plowman London SW
To e-mail, change noise into sound.

p cooper wrote:
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 have access to a Psion series 5MX palmtop computer, there is a
free program which may assist you. It is available at:-

http://www.hazchem.freeuk.com/sai1a.htm

If it is of value, please don't forget the fund at the bottom of the page.

--
Howard Neil

p cooper wrote:

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 .

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

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
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).

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.

Subject: tyre-road coefficient of friction
From: p cooper
Date: 31/12/04 07:12 GMT Standard Time
Message-id:

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, :-(((

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 Baker - Puma Race Engines (www.pumaracing.co.uk)

"Dave Baker" wrote in message
...
Subject: tyre-road coefficient of friction
From: p cooper
Date: 31/12/04 07:12 GMT Standard Time
Message-id:

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 (??).
snip

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.


--
Kevin Poole
**Use current month and year to reply (e.g. )***
Car Transport by Tiltbed Trailer - based near Derby

Autolycus wrote:


"Dave Baker" wrote in message
...

Subject: tyre-road coefficient of friction

From: p cooper
Date: 31/12/04 07:12 GMT Standard Time
Message-id:

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 (??).

snip


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.

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.






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.


Indeed.

p cooper wrote:

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 .


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.