Different ratios difference at 78 miles per hour MPG

Getting .25 mpg better won't justify speeding (especially at 80 mph) to maybe make tight appointments.

The speeds you're talking about are so far past the point of best mileage that mpg is basically irrelevant.

If you're just entertaining yourself with this daydream, go do the research yourself.

You can find rough estimates of drag & rolling resistance on a semi. Call CAT, Cummins, or Detroit & ask them for a BSFC curve at whatever HP you want. Download Eaton's gear ratio charts for all their trans. Find a gear ratio & start plugging in #s to find engine RPM for diff combos.

And finally, plug the #s in your calculator & hit that = sign. There's all the MPG #s you could ever want!

I'll bet you it's gonna be horrible.

 

The title was changed. The original title was dealing with differences between a 13 and 9 etc.

When changes come up, whatever I put on or anyone else puts in prior to change is essentially moot.

 

Rounding up? And learn to count...I see 2 pages, not 4.

 

I just don’t buy the slow down and get better fuel mileage crap and here’s why!
500 miles @ 7 miles per gallon 60 mph =74 gallons of fuel @ 3 dollars =222.00
600 miles @ 6 miles per gallon 70 mph = 100
Gallons of fuel @ 3.00 per gallon = 300
Let’s say your load pays three dollars a mile so you made an extra $300 -$78 extra in fuel so you actually net 222.00 extra !
If you have a dedicated route then yes slowing down makes sense especially if you have plenty of time to make your route but if you’re just out here hammering away every day trying to make extra money a little more speed pays for it self!

 

Lotta speed haters on this thread. Maybe a lot of guys with weak or govern trucks. Whatever happened to states with high speed limits, open roads, and time sensitive freight? All the time, seems slow trucks I see every day doing 63 in an 80 mph zone. Then there speeding in a construction zone or through a little town.

 

Where is there a 78 MPH speed limit??

 

I see this thread going to h-e-double hockey sticks fast!