🚀 go-pugleaf

In article <359f210f.7127081@news.okc.oklahoma.net>,
   in@the.sig (E. Faubion) wrote:
>"Mark B." <spam_*this*_@see.my.sig> wrote:
>
>>> On the average dry roadway the c.o.f. will run around a .70 to a .80.
>>> Using an average of .75 your slide to stop distances come out a bit
>>> higher, namely 218 and 285 feet respectively, a difference of 67 feet.
>>
>>BZZZT!  Sorry, Earl, *WRONG ANSWER*   ...but thanks for playin'.
>
>Straight from Northwestern University and other sources and verified
>with numerous tests performed locally on a variety of roadways.  
>
>>Your "average c.o.f." figures appear to be coefficients of *SLIDING*
>>friction, and your reference to "slide to a stop distances" leads me
>>to believe you don't understand much basic physics. 
>
>X speed to zero is X speed to zero no matter how you slice it. 
>
>>The stopping distances Dan Manes quoted have *NOTHING* to do with
>>"sliding to a stop" -- they're for *controlled* braking (without
>>wheel lock-up).
>
>Perhaps the term "slide to stop" threw you off.  Use 'deceleration to
>stop' if you prefer.  I apologize for the term I used, it's one that
>was used prior to ABS and it persists today even though it actually
>refers to the distance a vehicle travels while decelerating from one
>speed to another, or in this case, to a stop.  One reference book I
>use now refers to it as, "distance required to bring a vehicle to a
>stop."
>

Far better terminology.

>>model becomes much more complex, but as a first approximation, you
>>would use the coefficient of rolling (static) friction -- which is
>>generally *much* higher than the sliding c.o.f.
>
>How much higher?  I've performed tests with and without ABS and found
>that on average the difference is seldom more than .05 and often less.
>

Earl, with these tests, were you braking with fully locked wheels in the 
non-ABS car? If you wern't, you were getting close to the static coefficient 
of friction. A very basic rule of thumb for rubber on bitumen would be (for 
the case of typical materials used in road and tyre construction-please note 
the deliberate defining of conditions) is a CoF of 1.0 static and 0.8 kinetic.

>>Your c.o.f. is (reasonably) accurate for reconstructing accidents
>>based on skid-mark measurements, but *competent* (or ABS-equipped)
>>drivers don't leave skid marks
>
>BZZTTT!!!  Wrong answer.  ABS does leave a skid mark.  An experienced
>accident investigator and many novices know this.   I'll give you some
>leeway since you apparently aren't in the recon or investigative
>field.
>
>>I won't even attempt to give an "average" rolling c.o.f. because
>>it's virtually useless for accurate braking-distance predictions.
>
>Yet it holds up in a court of law involving multi-million dollar
>lawsuit.   How can that be?  I've run tests on rolling resistance too.
>

Earl, it could be because lawyers do not have much of a clue about physics. (I 
am a physicist, my brother is a lawyer, so you could say that I know from 
personal experience). Seriously, the average lawyer would not have the 
knowledge to dipute the "average" CoF's that are put out, but rest assured 
that I could destroy such a case with relative ease. Where it is not easy to 
dispute would be if the car was, say above the speed limit, even using a very 
high value for CoF. But if you went to court using a figure of 0.7 CoF to 
state that I was doing 80mph, and not 70mph, I would destroy your case. If you 
had calculated about 130mph in a 70 zone, you would have me as your result 
would be well within possible error bars.

>>More than anything, braking performance depends on tire selection
>>(size, profile, tread design, rubber compound, etc);  it makes no
>>sense to "predict" braking distances -- they *must* be measured.
>
>You should research what c.o.f. is before you go any further.  Tire
>size and all that has very little to do with c.o.f. on dry pavement.
>The only time it'll have much effect is if we have a crash involving a
>vehicle that has been modified from its original factory
>configuration.
>

No, tyre size does not have any real effect. However, compound does (both tyre 
and road surface), and suspension and braking system design and condition will 
change how close you can get to that theoretical value for the compounds in 
use.

>>The following graph (view with fixed-width font) shows the approx
>>range of stopping distances (reported by various auto-rags) for a
>>few dozen late model cars/minivans/SUVs/pickups.  I just picked
>>some samples from the performance summaries on www.autosite.com.
>
>Nice data but you must remember that most auto magazines and such
>sites are for-profit enterprises where the manufacturers of the tested
>vehicles and tires actively advertise thereby creating a conflict of
>interest.  While the data may in fact be good it is typically best
>case scenarios that don't conform to what we find out in the real
>world.    
>

Are you trying to say that tests worldwide are conducted to appease 
advertisers? I'm sorry, but that is blatant nonsense. Earl, the CoF of tyre on 
road are nowhere near as homogeneous as you seem to believe. (Is it deja-vue, 
or have we had this discussion before?)

>>The basic logical flaw in that thinking is that it only considers
>>accidents *after-the-fact*.
>
>How on earth can they be considered before the fact? 
> 
>>Nobody suggested that speed doesn't
>>contribute to severity of damage *once a collision has occured*.
>>Of course it does!
>
>That's only part of the equation.  In some crashes speeding is a
>factor, in others it is the cause.  These cases are on file in the
>thousands and in spite of all the rhetoric claiming they are incorrect
>weI have yet to see any of them overturned because a speed proponent
>argued what's being argued here.  That one fact alone speaks volumes.

Earl, could it be that it is because of ignorance of the facts, and distortion 
of analysis of the data by "the authorities". Never underestimate the 
stupidity of the legal system.

>Add this to the fact there is no one who routinely drives the speed
>limit doing the arguing and I think you have a pretty clear picture of
>what this is all really about.  In two words, sour grapes.
>
>I've said it before and I'll say it again.  I like to drive fast, I
>always have, and if there was any way I could make the numbers justify
>that I would have done it a long time ago.  But try as I might there
>I've been unsuccessful and I do not believe in coverups.
>
>>The rational for setting speed limits based on traffic engineering
>>principles (85th percentile) is to reduce accident *frequency*.
>
>The 85th percentile is nice but it is a variable, not a constant, and
>that is its major failing.  As speed limits are increased and people
>start driving faster the 85th percentile also goes up, yet the roadway
>and the environment are the same.  Ask any reputable traffic engineer
>and you should hear the same thing.
>

Earl, 85 percentile limits are set based on that roadway having NO speed 
limit. In efect, what it is saying is that you are making the assumption that 
15% of people driving are suicidal maniacs, which is not the case (far too 
severe).

>>Yes, the accidents that occur at higher speed WILL be more severe;
>
>Yep.
>
>>but the goal is to minimize the (Severity x Frequency) product --
>>globally across the entire road network.  For example, if raising
>>limits on the interstates diverts traffic from (more hazardous)
>>secondary roads, accident/fatality rates (per MVM) will decline.
>
>The goal is to reduce (or better yet, eliminate) accidents.  When an
>airliner crashes no stone is left unturned until we discover the cause
>and then steps are taken to prevent a reoccurrence.  Yet when a car
>crashes we, as a society, seem to say it's acceptable and it's no big
>deal because it'll never happen to us.  It's no wonder flying is safer
>than driving.  We need to wake up and pay attention to what's been
>causing crashes and quit pushing our heads into the sand and
>pretending the causes are always the violations committed by other
>drivers and never those committed by ourselves.
>

Yes, and this means looking into ALL areas affecting crashes, not just ticking 
the speed box and thinking that the job is done, and that the more that we put 
the fear of god into the  average driver WRT speed, the safer the roads are 
going to be. To me, that is putting your head in the sand.

>>The AVERAGE honesty of traffic-enforcement jurisdictions is of little
>>solace to the cross-country traveler.
>
>I've traveled cross country many times and never had a problem.  And
>before you say that's because I'm a cop, no, there's no way any of
>them could have know that since I never got stopped.
>

I have personally been booked for speeding illegally. There were a total of 5 
inconsistencies that were in this one case. I got off before it even went to 
court (phoned the sergeant in charge of the traffic operations group). Point 
is, there were a number of other bookings that were made that day by this same 
officer that would have been illegal as well.

>>In a matter of a few hours, I
>>probably drive through *dozens* of perfectly honest municipalities --
>>but if only 1 in 1000 is ambushing innocent out-of-town victims, I'll
>>get nailed about once a year.  
>
>Boycott. Refuse to violate their idiotic laws and the problem is
>solved.  If that doesn't teach them a lesson I don't know what will.
>

Would you have told those that conducted the Boston Tea Party "Boycott. Refuse 
to violate their idiotic laws and the problem is solved.  If that doesn't 
teach them a lesson I don't know what will." In this case, the boycott would 
take the form of not buying any tea!! Sorry, Earl, I know that this boycott 
thing is one of your favourites, but it is really stupid.

Dennis