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Old 01-09-2016, 03:35 AM   #1
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CUMMINS ENGINES REPORT: The Physics of MPG

Twas looking for MPG research on speeds below 55mph and ran across an interesting report sponsored by Cummins Engines.

The full report can be seen here:

http://cumminsengines.com/uploads/do...whitepaper.pdf

Here are the highlights:

Rock-Solid Rules

 Every 2% reduction in aerodynamic drag results in approximately 1% improvement in fuel economy.

 Above 55 mph, each 1 mph increase in vehicle speed decreases fuel economy by 0.1 mpg.

 Worn tires provide better fuel economy than new tires, up to 7% better fuel economy.

 Used lug drive tires can get up to 0.4 mpg better than new lug tires.

 Ribbed tires on the drive axles provide 2–4% better fuel economy than lugged tires.

 Every 10 psi that a truck’s tires are underinflated reduces fuel economy by 1%.

 The break-in period for tires is between 35,000 and 50,000 miles.

 Tires make biggest difference in mpg below around 50 mph; aerodynamics is the most important factor over around 50 mph.

 The most efficient drivers get about 30% better fuel economy than the least efficient drivers.

 Idle time is costly. Every hour of idle time in a long-haul operation can decrease fuel efficiency by 1%.
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Old 01-09-2016, 07:49 AM   #2
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Some interesting data there, must have taken a long time to research and compile it. Important to note that alot of it only applies to trucks though, and isn't necessarily true for light passenger cars. I like the 50,000 mile true break in though, jeez I'm lucky to get 5000 from a set! Tyres do account for a lot of your economy, would be interesting to see the different results for size differences too. In my case, a car with 16" alloys as appose to my 17" will get around 5 MPG more overall, at least in the lab tests anyhow.

In a smaller lighter vehicle increasing speed may increase your economy. I read a report not so long ago where a car was tested at various speeds and it used less fuel at the higher cruising speed. That's why it's important to do your own experiments, you might be driving slow on purpose to save fuel when there's no need.
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Old 01-09-2016, 10:14 AM   #3
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Yeah. After I posted it to Fuelly, I dived into the report. It's well worth checking out, Draigflag.

BTW, what is a "Draigflag"?
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Old 01-09-2016, 10:24 AM   #4
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Ha well Draig or Ddraig if it follows a vowel, is Welsh for Dragon, as in the Red dragon (Draig coch) on our country's flag - Draigflag get it? Without sounding too patriotic, has to be one of the coolest flags in the World, I mean how many flags have fire breathing mythical creatures on them?
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