This formula correlates rpm and speed... nothing else. It was govornment mandated that peak torque should coincide with 55 mph. That is why vehicles with standard rear-end ratios and standard tires all have there peak at 55 mph. It has nothing to do with with wind resistance. There is no factor for wind resistance. This simple formula will NOT get the maximum out of your fuel. If (ideal cruising speed) is a compromise between speed and fuel consumption why did you claim best mileage? A compromise with speed indicates an arbitrary value being placed on your windshield time. When in traffic, it places a value on everyone elses time. According to this, Your ideal cruising speed would increase with each additional passenger. You have made incorrect assumptions about the defenition of this formula. A more practical use of this formula would be to plug in your cruising speed (mine is ten over by the way) and extrapolate what tire size or gear ratio will optomize that mileage. If you want to find out what your "ideal cruising speed" is (according to your formula), Drive down the road until you reach 2000 rpm, then look at the speedometer. This is the ONLY thing this formula tells you.

 

Ok, simple prove me the opposite and I will be happy.
Including the tire size and "knowing your speed is over 60 shows simply an oversized tire not suiting your gears. I think even Ford engineers know that.
I guess you know about speed and correlated wind resistance. Power to overcome wind resistance is a squared function not linear.

Please perform a coast down test and tell me your Brake Specific fuel consumption. I will be happy to hear about your results.

You didn't read carefully. As you state in your first sentence and absolutely right it correlates rpm and speed and neglects wind resistance because speed limit prohibit to drive faster than 70 miles anyway.

So your usable range is between 0 and 70 miles.

But to have or to get these rpm numbers you have to know your torque peak which in easy words explains best engine effi. I don't talk about peak hp-it's peak torque.
And yes, Diesel engine manufactures have a relative flat torque cuve compared with gassers. That makes gearing in a diesel so important.

So what about germany, we don't have your 55 miles speed limit.
We have either 62mph or no speed limit, aren't those cars sold to the US?
They don't have a US specific gearing...

Please let me know is you are interested in those calculations, I will pull them out and copy them for you. Shouldn't be a problem to share knowledge.
Those formulas aren't black magic

 

Can you back pedal any faster? Are we now speaking irrelevent jibberish? I have proven your initial statement false. This formula does not give you the speed at which you get the "maximum out of your fuel". Slower will increase mielage by an inverse square relationship. If you graphed mielage vs. speed, You would see only a miniscule insignificant inflection point at max torque rpm.

 

it gives you the speed the engine is running at it's most efficient

I believe thats where this is going.

 

I'll agree to that as long as no more is read into it.

 

Otherwise you can keep it simple.

6% fuel saving by decreasing 10% weight ( barely possible)
3% fuel saving by decreasing 10% air resistance ( not possible at all, fixed)
2% fuel saving by decreasing 10% rolling resistance ( possible with using tires with street thread and a huge amount of silica)

I used the formula because no one here modifies his truck to gain higher mpg.
It's a static value. Don't try to tell me you are able to work with dynamics.

You still don't get the combination of torque and speed and related fuel consumption.

 

Thinking about it... you would want to be driving at a stable rpm (one above peak torque) if you cruise above peak torque any hills or headwinds will cause the rpms to lower and cause the motor back into peak torque giving you the power to maintain speed, cruising below peak torque will be harder to regain rpm under the same situation leading to more speed variances..

and then we could go into volumetric efficiency of a diesel and..... i'll just stop right there


think about it... cruising faster up a grade and letting the rpms fall some while adding fuel to maintain speed is a lot easier than starting at speed and trying to increase. eg. downshifting a gear vs lugging the current one.

 

I neglected rolling resistance, inclination, acceleration and braking resistance for that reason.
As you surely recognized(because you mentioned it) it's all in the formula above.
But it's simply not necessary to get a number where to start. Just keep the number of the highest speed as the static limit.
There is no increase above this number.

 

anyways.. it's way to many variables to calculate the true efficiencies..

what is really needed is to measure the amount of POWER required to maintain a certain speed, the smaller the better..

if we could manage to get a gauge to show current power being used...........
Thats peaked my interest, going to look into designing this.

 

Scan Gauge II should show that if you have OBDII...

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Or you could perform a coast down test to gain those numbers to evaluate the needed hp at 50mph- but that needs a good hour for the calculations.