MPH And Fuel Saving...
 

Is there a place to go, or could someone tell me if there is a real difference in how fast you drive and the fuel saving. I was told by an o/o that he saves hundreds of dollars per week in fuel because he only drives 60 mph as opposed to 70-72 mph. He said he showed and compared numbers with a friend who drives fast and the saving was a big difference. He has a different tractor then his friend but the loads they haul are the same weight.

He told me to fill up and drive a tank full out at 60 mph then check it. What is your opinion?

Thanks
Neckster

It depends on how the truck is spec'd. My truck gets better fuel mileage at higher speed, higher rpm than it does chugging along. I can chug down the highway at 5.3-5.4 at 60mph in 13th gear and turn 1300 rpm, or I can step it up a bit to 70 and turn 1500rpm and get 5.8-6.0 depending on terrain, etc. of course. I've heard that the newer trucks can run lower RPM without sacrificing fuel mileage, don't quote me on that though.

Last night my computer showed a 1% savings by slowing from 65 to 55. That's about $20 a day.

I have a Cat C-12 and run around 68-72 mph and get 6.3 mpg. I don't know if that's good or not. I've never tried going 60 mph, that's slow, however I did try 63 mph and that was not to bad.

Neckster

An example would be the CAT C-15 ACERT engines. They shouldn't be cruised at more than 1500 rpm.

Neckster- As said before, the newer engines have been rumored to benefit from lower RPM and speed, so it may work the best for you. I can't stand driving that slowly either, but I do know that I tried it one night, dropped the cruise down to 63 or something in 12th gear and cruised and when I got to where I was going, I wasn't as tired or stressed out feeling, as I would have been from doing 70-75. Sounds goofy, but just my findings.

PackRat-I told you not to quote me, dangit! :lol:

The "sweet spot", for my 3406E was at 1400rpm, for my Acert, it's about 1325rpm.
But there is more to it, than just RPM, the same RPM, sure use a different amount of fuel, at 20, or 40psi boost.

And nobody could change the law of phythics, higher speeds=higher air resistance=more energy=more fuel, something like that! :)

And the less airodynimic truck consumes more fuel, for the same reasons.

I'm not entirely sold on the RPM differences. I've tried it out several times. Cruising in 12th gear vs 13th gear. At 60 mph, that's a difference of 1400 vs 1600 rpms.

According to the computer, there was just no difference at cruising speed. However, climbing a hill, because the engine is in the higher RPM range, it will inject a bit more fuel. The 13th gear will just slow down a bit, while the 12th gear just powers along. I think that's where most of the difference is.

There is a much bigger difference in speed though. Solo is right, as you increase speed, wind resistance goes up exponentially. The horsepower you use to push through this air is "wasted" just to keep your current speed.

I should edit this. I meant to type 10%.

And in the interest of full disclosure, mileage went from 9.25 at 65 mph to 10.03 at 55 mph bobtailing with a T6 KW/N14 Cummins 410hp, 3.90 rear gear.

I had always thought the computer on this truck was set up for US gallons, but now I'm sure. I can't imagine I was getting 10 mpUSg.

And why not? I was getting close to 11mpg, cruising bobtail at about 64mph.
Not a computer #, actual, at the pump.
C-15 CAT in T600 KW. :D