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Discussion Starter #1
According to GM the volt engages the engine directly to the wheels at about 70mph which improves mileage about 10-15%. Does that mean it might be more efficient to drive at around 70mph rather than 69mph? Anyone been able find a sweet spot for max speed and mileage?
 

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It's more complex than that. In the right condiitions, the engine can directly connect to the wheels at speeds as low as 35 mph. If you are driving at a steady speed on the highway at 45 mph or above while in CS mode, very likely the engine will be driving the wheels.

Below is a link to a forum thread that explains it and includes a video.

engine drive engagement thread

The bottom line, just drive the Volt at the speed you want to drive, and let your Volt figure out what mode to go to. It's pretty smart and will normally give you the optimal drive combination for the speed and road conditions.
 

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I don't have any numbers or charts to back this up, Bu 2.5 years of driving 50 miles per day, my gut tells me that 60-65 mph is the sweet spot. Go 70+ and your electric range drops dramatically, and 50mph will increase range, but the "overdrive" mode where the ICE contributes to propulsion doesn't kick in. If you have a G1 new enough to have the KWh gauge on the DIC, then you will see concurrent energy from the ICE and regen while cruising when on a flat spot. The regen will increase on any slight downhill slope, and you will see regen disappear on subsequent uphil slopes. So that flat, continuously moving with some regen is what you're looking for.

Again, no charts, data, or proof, just a gut feeling based. On many, many daily runs trying every permutation.

In the wintertime the formula changes. To avoid freezing to death, it's preferable to run the ICe early to generate engineer heat and avoid the resistive heat that saps the battery.
 

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Most gas cars will reach their peak efficiency from about 40-55 mph, any more than that and aerodynamics will dominate. EVs tend to peak even lower than that driving on electric since they are more efficient, maybe 25 or 30 mph. However, most are only single gear and start to get out of efficient range at high speeds. Volt has an electronic CVT so it varies the ratio.

The 10-15% is not sudden as mentioned, depending on torque needed it might be at lower speeds.

If your Volt shows KW being used, if you minimize that number at speed you will maximize your mpg.

The only real trick is use Hold mode at high speeds if you have it and plan to use entire EV range, as plain EV mode will be operating less efficiently at high speeds, but range won't last long at 70+ mph anyway. Save EV miles for lower speeds when possible.
 

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...

In the wintertime the formula changes. To avoid freezing to death, it's preferable to run the ICe early to generate engineer heat and avoid the resistive heat that saps the battery.
Hmm, "engineer heat" ehh. Is that the kind of heat that is generated when the technically inclined have to deal with the greater non-technical populous? :rolleyes:
 

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If you really want max mpg, reducing aerodynamic drag is the most important thing to do. The optimum speed is likely 40 mph or less, maybe as low as 25 mph. You can also cover all the body and door seams with tape, and other even more extreme measures if you are into all that. :)

GSP
 

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If you really want max mpg, reducing aerodynamic drag is the most important thing to do. The optimum speed is likely 40 mph or less, maybe as low as 25 mph. You can also cover all the body and door seams with tape, and other even more extreme measures if you are into all that. :)

GSP
I am sort of surprised that "high efficiency" cars like the Prii don't come with gapless body panels where the gaps are covered over with some kind of high tech equivelent of weather stripping. Flexible so panels can still expand and contract but don't leave an air gap. Even door/hood/trunk openings could be made this way.

Keith
 

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JeremyK crated this graph a long time ago. It looks about right from my perspective with (40K miles experience).


There is another graph from Car and Driver,



But this one looks a bit suspect in my experience. However, if you need permission to drive fast, use the second one ;).
 

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I do a fair amount of distance driving so I have been quite interested in efficiency while running the rEX.
Fortunately I take some of the same routes repeatedly so I was able to vary my process while driving essentially the same conditions.

So under conditions where you A) are going to run out of battery and B) will be doing some distance highway driving, it seems from my rough numbers that the crossover point is about 47 mph.

In other words if you are going to use electricity at the start (in town) and finish (in town) and have highway in the middle, you should wait on "HOLD" mode until you cross over about 47 mph to get the most efficiency from the rEX.

I achieved 39mpg (in rain) and 41mpg (in perfect weather) pure rEX at 70mph on long trips to Montgomery AL doing this.
 

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Discussion Starter #12
If the car and driver graph is correct, you get better mileage going 70 than 60 or 50. So why crawl around when you can get better mpg going 70. Hard to believe but amazing if true. This was the kind of information I was looking for.

JeremyK crated this graph a long time ago. It looks about right from my perspective with (40K miles experience).


There is another graph from Car and Driver,



But this one looks a bit suspect in my experience. However, if you need permission to drive fast, use the second one ;).
 

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JeremyK crated this graph a long time ago. It looks about right from my perspective with (40K miles experience).
*snip*
There is another graph from Car and Driver,
*snip*
But this one looks a bit suspect in my experience. However, if you need permission to drive fast, use the second one ;).
If the car and driver graph is correct, you get better mileage going 70 than 60 or 50. So why crawl around when you can get better mpg going 70. Hard to believe but amazing if true. This was the kind of information I was looking for.
The C&D starts at 40 mph, which makes direct comparison a bit more difficult, but I can unequivocally say that C&D was just making numbers up. Sure, the Cruze Eco might have better mileage than the Volt at sub-67 mph speeds, but the Volt's mileage improves with every mph slower than 65 mph. With my cruise control set at 50 mph on flat ground, I was seeing over 50 mpg. That was a hot day, sure, but not hot enough to result in 10 mpg better fuel efficiency than C&D's estimates.

JeremyK's chart, on the other hand, appears accurate, though I can't vouch for the sub-20 mph mileage.

Regardless, to answer your question: The efficiency improvement provided by the Volt's ICE connecting directly to the drive line will not offset the increased energy requirements of going faster. \p
 

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When I travel to Tampa which is 120 miles away from me, I run strictly on ice when I leave my city, and I average between 47 & 48 mpg, and I travel the speed limit whatever it is.
When I get on I-4 in kissimmee the speed limit is 70 mph
 

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The C&D starts at 40 mph, which makes direct comparison a bit more difficult, but I can unequivocally say that C&D was just making numbers up. Sure, the Cruze Eco might have better mileage than the Volt at sub-67 mph speeds, but the Volt's mileage improves with every mph slower than 65 mph. With my cruise control set at 50 mph on flat ground, I was seeing over 50 mpg. That was a hot day, sure, but not hot enough to result in 10 mpg better fuel efficiency than C&D's estimates.

JeremyK's chart, on the other hand, appears accurate, though I can't vouch for the sub-20 mph mileage.

Regardless, to answer your question: The efficiency improvement provided by the Volt's ICE connecting directly to the drive line will not offset the increased energy requirements of going faster. \p
Agreed. That C&D graph is nonsense. As far as the engine connecting up in series/parallel mode to the wheels, that will already be happening at 50 mph and actually at speeds down to 36-40 mph. An Idaho National Labs measurement claims the Volt can get up around 70 mpg at a steady 45 mph although I have not tried to verify that. At speeds under about 63 mph the first generation Volt likes to generate and store some energy into the battery with the engine running and then run on battery for awhile before restarting the engine. This can cause some confusion when estimating your own gas mpg at lower highway speeds during shorter trips -- over longer trips that effect on perceived mpg will average itself out.

The 2nd generation Volt operates more efficiently than the 1st gen at slower vehicle speeds (under 36-40 mph).
 

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At speeds under about 63 mph the first generation Volt likes to generate and store some energy into the battery with the engine running and then run on battery for awhile before restarting the engine.
I have noticed that on my longer trips now that I have a version of the Gen 1 that displays kW. This needs to be verified, but my assumption based on observing how it operates is that the Volt attempts to run the ICE under as efficient of a load as possible. So, when the ICE produces excess energy, it feeds back to the battery, and when it is more efficient to run the ICE at a lower load than is required to maintain speed, it draws from the battery to cover the deficit.
 

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That sounds like a fun little project. I'm surprised no-one has tried to replicate it yet.
I agree. I have some areas where I could test extended driving at 45 mph. Unfortunately, very few of those areas are flat, and that could taint some of the numbers. Some owners have been able to hit 70-80 miles using ~10 kWh of electricity in slow (~25 mph), flat driving, so my guess is that 80 mpg is probably the upper limit for the Volt using the ICE.
 

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I quickly
I have noticed that on my longer trips now that I have a version of the Gen 1 that displays kW. This needs to be verified, but my assumption based on observing how it operates is that the Volt attempts to run the ICE under as efficient of a load as possible. So, when the ICE produces excess energy, it feeds back to the battery, and when it is more efficient to run the ICE at a lower load than is required to maintain speed, it draws from the

This may explain why the yellow bar zips up to the battery when I step on the gas but no yellow no yellow bar zips from the engine from the engine which is not made sense to me. I am talking about the DIC display with the three bars. And kilowatt reading in the center
 

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I agree. I have some areas where I could test extended driving at 45 mph. Unfortunately, very few of those areas are flat, and that could taint some of the numbers. Some owners have been able to hit 70-80 miles using ~10 kWh of electricity in slow (~25 mph), flat driving, so my guess is that 80 mpg is probably the upper limit for the Volt using the ICE.
I have a 45 mile trip I take every 3 weeks or so in the upper Midwest, where everything is flat. I presented the idea to my wife who announced to me, "no way!".
 
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