Whats up with 62 mph?

Does anybody have any experience with one of those trucks that gets better fuel mileage at 70 mph than at 55 mph. I kind of think that is impossible given the extra horse power requirements to overcome wind resistance and rolling resistance at the higher speed, but I have heard people say it enough times that I would like to know how that happens. I would think something is wrong with the drive train, and when it hits the higher speed, the problem lessens, and the truck needs to go in for repairs. Looking at the Horse power requirement curves I have seen, I flat out do not believe it --- I expect you to lose at least 1.5 mpg at 70 vs 55.

 

It's truck stop BS normally from company drivers who never actually pay for the fuel and don't have the first clue what their fuel mielage is other than what a digital readout on the dash tells them, which is most of the time wrong... But clear cut 1.5 mpg from 55mph versus 70 mph? Possibly... With my truck the difference is about 8 tenths to 1mpg depending on conditions but that surely varies from truck to truck. The old you lose x amount for every mph over 55mp so that means all trucks lose 1.5mpg at 15 over just doesn't work out in the real world. Every motor/truck is different. Condtions vary... Some will consume much more and some not as much as others. None will get better mpg's going faster that' just common sense...

 

Well, technically it could happen getting better mpg at a higher speed. As is always the case, it is all about gearing. If the engine is outside its optimum power band at 55 and is at its optimum power band at 70, then it could happen. But then it could be argued that at 55 the driver could drop a gear and get the engine back into the band. But that doesn't always work. That next lower gear may actually have the engine too high or too low for 55. If the truck isn't spec'd appropriately for what the intended purpose is for, it really is kind of a cat and mouse game with fuel mileage. There is just not a one size fits all solution to the problem.

Strictly from an aero and rolling standpoint, it is not realistic to get better mpg at a higher speed. But there is more than aero and rolling resistance at play in the equation. Engines, gearing, tires, etc all factor into it. For instance, the way I am geared, 60 is my optimum for my particular engine. 55 has me either too low in the band in one gear, or too high in the next one down. That is if I am pulling any weight. Bobtail or empty, who cares.

 

They could lower the speed limit to 55 like they did in the seventies. Bet that would turn the CBs on.

 

CB's are off cause nobody speaks english

 

Habla Espanol gringo?

 

Really when other's have their C.B.'s ON I turn mine OFF.