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Author Topic: Tire inflation: MPG versus comfort  (Read 4146 times)
johns4104s
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« Reply #15 on: June 04, 2009, 03:18:43 PM »

Elkhedge,

I for one had not caught the Axel weight issue, Which reminds me I need to weigh mine to be sure my pressures are right.

Thanks

John
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Eric
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« Reply #16 on: June 04, 2009, 04:02:50 PM »

We'll mark that one for a "special" moment on my part Wink
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gyrocrasher
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« Reply #17 on: June 06, 2009, 08:04:44 PM »

.



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I already keep the MPH at 65 MPH to decrease fuel usage.  I discussed perhaps even going to 60 MPH last summer, but everybody else on the trip didn't want to spend an extra 3 hours in the bus each way, plus being 15 to 20 MPH slower than other traffic out west gets dangerous.


FWIW, That is an oft-quoted but completely unsupported statement.  AFAIK, no traffic safety studies have ever found that vehicles traveling below the posted limits (within reason, also usually posted) are less safe.


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(Speed limits on I80 from Nebraska to California are mostly 75 MPH.)
-Sean
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https://secure.truckflix.com/news_article.php?newsid=1460

http://www.landlinemag.com/Special_Reports/2009/Apr09/040209_ohio_split.htm

The only speed limit policy that makes sense is to have all vehicles traveling at the same speed. It is a welcome change in Ohio that is long overdue,” said Todd Spencer, executive vice-president of the Owner-Operator Independent Drivers Association.

“We are appreciative of the lawmakers recognizing the importance of this issue and once and for all resolving it.”

After days of intense negotiations, Senate Republicans and House Democrats meeting in a conference committee were able to work out their differences on the transportation plan. The full House and Senate approved the budget earlier in the day, setting the stage for Strickland to sign it into law.

Among the changes endorsed by lawmakers is the elimination of the provision in Ohio law that set up a slower speed on interstates for vehicles with a gross weight of more than 8,000 pounds. Speed limits on other roadways will remain unchanged.

Currently, large vehicles are required to travel 55 mph – 10 mph below the 65 mph limit for other vehicles. With the bill’s passage, all vehicles traveling on interstates soon will be cleared to drive 65 mph.

Owner-operator and OOIDA member Lewie Pugh of Freeport, OH, was pleased to hear about the action of lawmakers. He said that truckers in the state have touted the safety benefits of all vehicles traveling the same speed for years.
 


Not to be contrary, Sean, but I think there might be some evidence to the contrary. Smiley I realize the references are about speed limits,but you get the point. Smiley Mitch
« Last Edit: June 06, 2009, 08:23:16 PM by gyrocrasher » Logged
Sean
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« Reply #18 on: June 07, 2009, 03:51:18 PM »

...  AFAIK, no traffic safety studies have ever found that vehicles traveling below the posted limits (within reason, also usually posted) are less safe.


... The only speed limit policy that makes sense is to have all vehicles traveling at the same speed. It is a welcome change in Ohio that is long overdue,” said Todd Spencer, executive vice-president of the Owner-Operator Independent Drivers Association.
...
Not to be contrary, Sean, but I think there might be some evidence to the contrary. Smiley I realize the references are about speed limits,but you get the point. Smiley Mitch


Actually, you are being contrary.

Note, please, that I said (qualified by "AFAIK") that no studies have found that vehicles traveling below posted limits are less safe. I have added the bold emphasis to highlight the difference between this statement and the articles you cite, which
  • Do not cite or even mention any formal scientific studies.
  • Do not discuss self-selected travel speeds but only deal with posted limits being different for different types of vehicles.
  • Are clearly talking about a legislative change brought about by political action from the powerful trucking industry lobby.

So, yes, I get the point.  The point has nothing whatsoever to do with my assertion that choosing to drive at a speed below the posted limit makes you less safe.

Now, if you would like to cite evidence to the contrary (as opposed to speculation, or the political machinations of a special interest group), I would be happy to review it and revise my opinion.  But I spent too many years in the highway safety business for these sorts of unsupported arguments to be persuasive.

-Sean
http://OurOdyssey.BlogSpot.com
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gyrocrasher
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« Reply #19 on: June 07, 2009, 04:10:04 PM »

I stand corrected. Mitch
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RickB
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« Reply #20 on: June 08, 2009, 09:00:33 AM »

Hey All,

At the risk of sounding incredibly stupid I have always had an issue with the MPG issue.

My thought is this:

Using the earlier description of the difference of 7 and 8 mpg translated into three extra hours of running time between his destinations.

Does the fact that Brian's series 60 was running three extra hours to accomplish this negate the saved fuel costs?

I mean on one hand he conceivably drives there at the higher speed which lowers his fuel economy but has him arriving 3 hours earlier, on the other hand he slows down and gets better fuel economy but his engine has to run an extra three hours to reach his destination.

I have never been able to get my brain around the concept in my head that says, hey I'm getting better fuel mileage but the extra time my engine spends running is time it wouldn't have been running if I was already there. Fuel costs cease when our engines aren't running...

I started this with the right phrase: "at the risk of sounding stupid". I am quite sure I am missing something here...

Rick
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belfert
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« Reply #21 on: June 08, 2009, 09:23:36 AM »

The engine is using enough less fuel per hour over the entire trip that running three extra hours is still more efficient.  It is all about the amount of fuel required to move the bus forward one mile rather than how much fuel is burned per hour.  Fuel usage measured in hours only really makes sense for stationary applications.
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Brian Elfert - 1995 Dina Viaggio 1000 Series 60/B500 - 75% done but usable - Minneapolis, MN
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« Reply #22 on: June 08, 2009, 12:02:34 PM »

Exactly!

Without the experience/learning it is counter intuitive! And that's why we, the great unwashed masses, continue to spend WAY too much money on fuel, having been fooled about the sociological meaning, or the flawed assumption about changed arrival times, of the speed we choose.

One of the less well known measures for wearing out an engine is how much fuel has been burned in it.

Not how long it has run or how far it has gone.

As for fuel efficiency, the fuel use charts for our engines are somewhat "U" shaped, there is a "sweet spot" in the middle revs somewhere that the engine uses the least amount of fuel per time interval, lower or higher than that, the engine burns more fuel per time interval. Some of the more recent engines have a more pronounced "V" shape to that graph, operate the engine outside of a fairly narrow sweet spot, the fuel economy will be VERY poor in relation.

So, running the engine closer to the sweet spot rather than wide open, will produce better fuel economy on two fronts, less work in pushing wind, and running the engine at an RPM which makes best use of the fuel.

happy coaching!
buswarrior

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niles500
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« Reply #23 on: June 08, 2009, 04:28:03 PM »

Rick - Mills are usually designed around "cycles" or revolutions - technically a mill that is designed and operated at one speed or RPM using a CVT (think hydrostatic drive) will be more efficient and outlast others - You don't have the problems associated with lugging, piston slap, heat, etc. - A mill designed to last 2 million cycles at an average 2 thousand RPM will should last 1 thousand minutes - there are many other ways to describe it, as BW did in fuel consumed, but they all assume an ideal operating range is being maintained - Fall outside that "ideal" and the life of the mill is shortened - HTH
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JackConrad
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« Reply #24 on: June 08, 2009, 05:11:32 PM »

One of the less well known measures for wearing out an engine is how much fuel has been burned in it.
happy coaching!
buswarrior
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many years ago at an FMCE convention, a speaker (I don't remember his background) was asked about oil consumption. His answer was that oil consumption should be based on fuel used, not miles traveled.  His reasoning was that heavier fuel usage= harder engine usage and this will cause an increase in oil consumption.  I o not know if this is true, but at the time it sounded reasonable. Jack
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