So I have taken the same route three different times, same time of the night, same tempurate (approx.) same weather conditions (no wind, clear skies)... now the only variable in this is my speed.

1st try at 65mph... 115 miles @ 17.6 mpg
2nd try at 60 mph... 115 miles @ 20.2 mpg
3rd try at 55 mph... 115 miles @ 24.7 mpg

Why is it that with a 10mph difference I get just over 7mpg less? Now these are all hand calculated mpg's, and I can't believe the difference. I'm going to be sticking to 55 mph on the highway from now on.

Can anyone chime in on the reason for this.

 

Your vehicle is designed to perform best @ 55MPH

 

Yeah thats a question I've always had. Is it speed the decreases your mileage or the fact that the truck hasn't shifted to the next gear yet? It seems like the engine couldn't use any more gas without the rpm's going up. Figuring on that, I always try to keep the rpms below about 1750 for highway cruising which is around 60 for me if memory serves. Is my logic flawed?

 

i get 20 mpg going 68 mph with my truck, and i don't have a bed cover, and it is a quad cab.

do you have the auto 4 speed, auto 5 speed, or 6 speed stick trans? i have the 5 speed auto myself.

 

i recently pulled a trailer up to northern az...like 75% of the way was uphill around 200 miles. I went 55 or under the entire way in tow/haul mode (i was behind my dad who was pulling a big ol horse trailer) and was amazed when i checked the milage. Around 22mpg [:-]
So i thought if i did that great i could come back and do even better. Coming downhill, tow/haul off/ no trailer, 55mph cruise when i could set it, coasted other times. Managed 26 mpg[:-][:-] this was all hand calculated from the trip OD and fillups at gas stations. I was amazed, but also a little scared as driving I-10 with all the big rigs going 80+mph gets a little harry.

From my understanding how engines/transmissions work (which could very well be entirely wrong), the engine will work harder in the lower gear right before it switches to the higher gear, burning more gas. So if you are crusing in 3rd gear at around 2K~ rpm right before it switches into 4th gear than you are going to burn more gas. If it switches into fourth gear it will have to work less and burn less gas. 55mph seems to be the optimal speed to keep it in the lower gear, keep it from needing a higher gear, and burning the least ammount of gas. Now if only dodge could engineer some settings that could optimize it at a little higher speed like at least 65...

 

Well I have a 6 spd manual. Now what are you guys running RPM wise at say 60mph? I run about 2300 RPMS. :-\

 

I'll check on my way home. I've got the 5 spd auto with the 4.7. Of course I've got the big tires so my rpms might be skewed because of that. 65 sure would be nice...

 

Hahaha.... well check the RPMs at 60, then cruise 65. :-P

 

Do yall have the V6 or something, I've got 15.5 reading on that thing on the roof. It's so effin' cool, but all it does is bear bad news[>:]...Reckon the little guy's wrong?

 

Nope, I have a v8. I think my final drive ratio may be a little higher than the automatics. And if so that would suck.