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-   -   Gas mileage behavior (http://www.ramforumz.com/showthread.php?t=46798)

elcabron 01-19-2010 08:38 PM

Gas mileage behavior
 
Hi everyone

I've noticed something that seems to be kind of odd. Appears to me that the faster you go (up to certain level) the lower your gas consumption is. Let me tell you more.

I live in Monterrey, Mexico I use my truck to drive from home to work (most of the times) I drive like 60 km every day (37 mi) and my average oscilates between 14.7 L/100km and 15 L/100km (15.6 mi/gal), my speed oscilates between 80 - 100 km/h. One day when I was in a hurry I was going like 120 - 130 km/h and my average at the end of the road was at 14.3 L/100km (16.4 mi/gal).

So my question is ¿Why if I'm going faster the truck spends less gas than if I drive a little slower? At both rates the MDS comes in action regularly.

Regards!

hemiv8dodgeram1500 01-19-2010 08:59 PM

I dont know but i noticed that to on my old truck

MightyBlueRam 01-19-2010 09:22 PM

This is an interesting article that explains your question.

http://auto.howstuffworks.com/fuel-e...uestion477.htm

GPSHSLAX 01-20-2010 01:18 PM

That article on road load is interesting but there is more to it than that as well. Remember that your gear ratio plays a role as well. As a general trend the fewer RPM your running at the less fuel you are burning per minute. At a given burn rate the farther you travel in the minute the higher the MPG. What this tends to work out to is that you get your best fuel economy in the low range of your highest gear. Of course you need to be high enough that the truck doesn't keep downshifting to maintain speed but you get the idea.

Dan 01-21-2010 12:00 AM

It's a balance of higher speed and lower fuel consumption- up to a certain point, the small amount of gas that it takes to move the truck a couple miles per hour (or km/h) faster is worth it in terms of efficiency. Of course, after that point, the increase in speed won't offset the increase in fuel consumption.

I get the best fuel mileage in my '09 at about 70mph (112 km/h).

Revolter 01-21-2010 12:28 AM

Quote:

Originally Posted by Dan (Post 141342)
It's a balance of higher speed and lower fuel consumption- up to a certain point, the small amount of gas that it takes to move the truck a couple miles per hour (or km/h) faster is worth it in terms of efficiency. Of course, after that point, the increase in speed won't offset the increase in fuel consumption.

I get the best fuel mileage in my '09 at about 70mph (112 km/h).

What rear axle gear ratio are you running?

09Hemi 01-21-2010 06:47 PM

usually the sweet spot it around 70-80 mph. somewhere in that 115-130 km/h. some vehicles are different depending on the design. but thats about the speed where your forward momentum keeps you going and the motor does not need to work that hard. Do you have a tonneau cover?? because most would claim that having one helps but in all actuality it does not. if you dont you get whats called the cyclone effect that boosts your MPG because the wind is moving so fast at that point that it goes in and creates a cyclone and forces the air right over your tailgate. and like stated the cyclone effect does not start until around that speed

Jack772 01-21-2010 08:14 PM

Mileage
 
I used 14.9 gal of gas to go 230 miles in my '09 Ram 5.7.
This figures to be abt 15.4 miles per gal. 90 mile of the 230 was on I 95. The rest was in town.
The rearend is a 3.21. On I 95 I set the cruise on 72 mph.
This was better than I got with my 5.4 Ford Supercrew.
I am happy with it.
Jack

Revolter 01-21-2010 09:04 PM

I drove 95% highway and the MPG indicator showed 18.8 and was still climbing when I reached my destination. I don't know how accurate it is but i'm really pleased if I got 19mpg. with 500 miles on the truck. No, I don't have a Tonneau cover, Yet. I just hope the 3.92 gear doesn't hurt MPG to much. Anybody with and 09/10 with 5.7 and 3.92 that has checked MPG on highway?

Dan 01-22-2010 09:52 PM

Quote:

Originally Posted by Revolter (Post 141364)
What rear axle gear ratio are you running?

I have the 3.55


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