going slower uses more gas. what??

[Tahoe_Hybrid]

i tried going slower just a little bit but it wastes more gas

whats going on here i was going normal speed gets me about 18-19 upwards of 22 but going a bit slower gets about 15-16mpg

[maanma]

Big engine ( > 1.0 L) and gearbox is not optimized for going (slow).

For example 2.0L I4 might be utilized better running only with 2 cylinders if cylinders were utilized normally in pairs. Sure this would need run unused cylinders valves open and separated exhaust system.

Bore is oversized to be effective.

Same problem lies in mini sized engines trying get fast. Bore size is too small and speed is achieved through high rpm.

[redpoint5]

What was the grade, and what was the initial speed vs slower speed? How did you measure and then calculate efficiency?

Physically, traveling faster takes more power, so there's no getting around that.

If the slower speed had the transmission downshift that might partially explain the difference. Generally, going as slowly as possible in top gear is most efficient.

[oil pan 4]

Below a certain speed yes. Even in electric vehicles too.
If I drive my leaf 20mph it won't go as far if I was driving it 30 to 35mph.
And hybrid vehicles are even more weird than gasoline.

[ksa8907]

I too have seen some very strange behavior from the onboard guessometer, I find best economy at 45-50mph with this hybrid truck. I do wish I had the hybrid aero treatments though.

[Tahoe_Hybrid]

Originally Posted by redpoint5

What was the grade, and what was the initial speed vs slower speed? How did you measure and then calculate efficiency?

Physically, traveling faster takes more power, so there's no getting around that.

If the slower speed had the transmission downshift that might partially explain the difference. Generally, going as slowly as possible in top gear is most efficient.

its pretty much a flat grade pretty much FLOORING it from 0 to 45 nets about 20-22


going slowly from 0 to 45 is a net loss of 9-10mpg it will read about 13-15mpg on the fuel meter whole time tell i reach speed ( 47-48mph) then jump to 23-29 on the meter


the top gear is at 30mph in 4 speed mode

EVT mode(eco mode) the top gear or ratio is at 47mph (sometimes shifts if I let off the gas) the engine is at 1050 to 1100 rpm 6th gear
i don;t think the trasmssion is messed up



Maybe the battery is too far depleted ?

it has a hybridized automatic transmission 4 speed launch gears 0-60 in 6.5 seconds (assuming a new hybrid battery)




6.0L engine if that matters i disabled the AFM as it's risky business keeping it enabled (replacement engine COST $6,000) or 2,000 to repair it

it's always in V8 mode....


the 2mode transmission does not down shift once in eco mode you can ride 1,000RPM to 0MPH ( DFCO )from 50mph

No engine braking, only from the regen which is very light almost undetectable ( unless on the "M4 gear" 4 speed fixed gears then you get engine braking )

[maanma]

Correcttion: Acceleration time does not effect energy needed for whole accelaration.

So my previous answer IS WRONG (forgive me):
Speeding up slower (longer in time) will save energy. Doubling time is halving the energy needed.

[Vwbeamer]

Generally best fuel economy is achieved at the slowest speed you can travel in the highest gear.

Most cars that works out at around 40-50 mph.

That's an over simple fication, and I can't explain the Leaf, since I believe it has a single speed transmission.

[redpoint5]

Originally Posted by Tahoe_Hybrid

its pretty much a flat grade pretty much FLOORING it from 0 to 45 nets about 20-22


going slowly from 0 to 45 is a net loss of 9-10mpg it will read about 13-15mpg on the fuel meter whole time tell i reach speed ( 47-48mph) then jump to 23-29 on the meter

We've all misunderstood your testing scenario. Our assumption is that you were holding a steady cruising speed, and the slower speed yielded worse fuel economy than a faster cruising speed.

You're describing acceleration, which is a rate of speed change. Speed is a constant number, like 45 MPH.

Gasoline engines are typically much more fuel efficient (power per unit of fuel) when operating around 75% throttle and around 2,500 RPM. The engine is very inefficient at lower throttle openings (slow acceleration).

It took an eternity staring at this before everything made sense to me, but it shows power per unit of gasoline in a typical engine.



There's hardly any penalty in efficiency by going full throttle, but plenty of inefficiency at 50% or lower throttle opening across the useful RPM range.

[maanma]

What we should look for is something like less than 25% (of max) torque. To minimize consumption in acceleration one must use best rpm for minimized torque.

Max torque is not to thing look for best mpg on acceleration. Maximixing torque will also maximise fuel consumption in acceleration. It is for maximal accelaration with most reasonable consumption.

I learnt best options with Fuel economy plugin for Torque app. It is very effective after use forwhile.