Re: [Phys-l] truck mileage

[Bernard Cleyet <bernardcleyet@redshift.com>]

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Personally I don't believe the data.

___________________
Joel Rauber
Department of Physics, SDSU
Brookings, SD 57007
Joel.Rauber@sdstate.edu
605.688.4293
----------------------------

Yo, tambien!


I suspect JD will weigh in here -- on the very non linear effect of  
drag w/ the disgustingly poor drag coefficient of a truck trailer  
combo, and?

In addition to the already mentioned compensation from a sl. slower  
speed.  Inflating the tires for the increased load may also be  
another explanation.

bc waiting.

p.s. just returned from Barstow hunting fossils.  I decreased the  
tyre p from ~ 35 + PSI to ~ 22 for the washboard road. [Does make a  
diff.!]   Curiously, no matter the conditions [medium and high (>65)  
speed hwy, slo on the dirt roads, city speeds, etc.],  the MPG was a  
constant 40 mpg.  On re-inflation (trip home) ~ 41 @ ~ 80 and > 45 @  
~ 65.  In cities as high as 50 mpg.  bc loves his new Prius w/ the  
back up camera.

On 2008, May 07, , at 15:22, Jack Uretsky wrote:

> Hi all-
>  	Of course all such data need to be taken with a few grains of
> salt, and driving habits can play a major role in the result.  But,
> consider the physics of a truck pulling a trailer at constant speed  
> on a
> level road.  Power required be the presence of the trailer is that
> dissipated by the rolling friction of the trailer wheels.  How much  
> does
> that friction increase when a load is placed obn the trailer?  I don't
> have much feel for the numbers, but it must be a small fraction of the
> added load.   The gal/mi is proportional to the friction force,  
> which is
> probably proportional to some power of the speed.  My conclusion is  
> that
> in all likelihood, a small decrease in the speed could compensate  
> for the
> added friction due to the increased load.
>  			Regards,
>  				Jack
>
>
>
> On Wed, 7 May 2008, Bill Nettles wrote:
>
> > I agree the data are questionable
> >
> > OR
> > the truck driver doesn't go as fast when he has 10000# of cows :)
> >
> > Is there a baseline gas mileage with a nonlinear increase  
> > (arctangent) as the weight decreases? Gas mileages are notoriously  
> > non-linear for most variables.
> >
> > > > > Kathy Daniel <kcdohs@comcast.net> 5/7/2008 4:02 pm >>>
> > I have quite an interesting problem that I cannot explain...
> >
> > Our Ag teacher set up this scenario for me:
> >
> > one 5000# truck gets about 18 miles per gallon
> > same 5000# truck pulling a 4000# trailer gets 8 miles per gallon
> > same 5000# truck pulling a 4000# trailer + 10000# of cows ALSO   
> > gets 8
> > miles per gallon.
> >
> > Any ideas why the empty and the full trailer both get the same
> > mileage?  This same pattern is also present in a different trailer  
> > and
> > truck combination.
> >
> > thanks,
> > Kathy
> >
> >
> > Kathy Daniel
> > Oakland High School
> > Murfreesboro, TN  37130
> > kcdohs@comcast.net
> >
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