GM Volt Forum banner

1 - 17 of 17 Posts

·
Registered
Joined
·
5 Posts
Discussion Starter #1
Weight will be pretty important in regards to fuel economy in addition to a bunch of other factors like driving habits. Personally the 64 km all-electric range of this car is more than enough for myself thus it would seem wasteful to drive around with a full gas tank.
Any word on how big the volt's fuel tank will be relative to current models?
Do you guys think it would be prudent to drive low on gas, or may I even dare to say: on an empty gas tank? And would the increase in mileage be worth it?
 

·
Registered
Joined
·
4,085 Posts
Weight will be pretty important in regards to fuel economy in addition to a bunch of other factors like driving habits. Personally the 64 km all-electric range of this car is more than enough for myself thus it would seem wasteful to drive around with a full gas tank.
Any word on how big the volt's fuel tank will be relative to current models?
Do you guys think it would be prudent to drive low on gas, or may I even dare to say: on an empty gas tank? And would the increase in mileage be worth it?
I heard that they are dropping the planned range down to 300 miles, leaving the range-extender to provide 260 miles. It's hard to say how big the tank will be, because they claim 150 mpg's sometimes, but I am guessing it would be anywhere from a 3 gallon to 6 gallon tank. I agree with you that I would probably only keep it under half full, unless I was planning a long trip.
 

·
Registered
Joined
·
695 Posts
Factors Affecting Range

GM has placed 4 factors in order in regards to their effect on the Volt's range,

1) Aerodynamics
2) Power consumption by accessories (AC, radio, defroster, etc.)
3) Weight
4) Tire rolling resistance

I estimate an 8 gallon tank for the Volt. The weight of 8 gallons of gas is about 50 lbs. For the difference between 3000 lbs (no gas) and 3050 lbs (full tank), I bet you would be hard pressed, even in laboratory conditions, to tell the economy difference based on the added weight of the fuel.

Conclusions: Drive it with whatever amount of gas you want, the effect on negligible.
 

·
Registered
Joined
·
1,916 Posts
Several of the recent articles after last week's press junket mention that they have decided to reduce the tank as Jason mentions, but I recall reading they expect 400 miles range. They have been stating about 50mpg fuel economy in generator mode, which would mean about 7 gallons. They mentioned saving space, weight, and money but it may also have to do with stale gas. They have repeatedly mentioned this as a concern and the bigger the tank, the longer a full tank will last.

I haven't heard of nor can imagine issues with partially filling the tank but the engineers did seem to shutter at the thought of no gas. That could cause issues.
 

·
Registered
Joined
·
125 Posts
What about regeneration efficiencey

GM has placed 4 factors in order in regards to their effect on the Volt's range,

1) Aerodynamics
2) Power consumption by accessories (AC, radio, defroster, etc.)
3) Weight
4) Tire rolling resistance

I estimate an 8 gallon tank for the Volt. The weight of 8 gallons of gas is about 50 lbs. For the difference between 3000 lbs (no gas) and 3050 lbs (full tank), I bet you would be hard pressed, even in laboratory conditions, to tell the economy difference based on the added weight of the fuel.

Conclusions: Drive it with whatever amount of gas you want, the effect on negligible.
I'm a little concerned that the list does not include electric motor efficiency and regeneration recovery efficiency.
 

·
Registered
Joined
·
695 Posts
Energy Priorities

I got the energy priorities from the following link:

http://www.autobloggreen.com/2007/12/12/volt-aero-and-styling-touring-the-e-flex-design-studio-and-gm-w/

Here is the quote of interest:

"Driver behavior is clearly a factor for both traditional and electric cars. Beyond that, on traditional cars, factors like mass, aero drag and rolling resistance come into play in that order. In testing and simulation GM has found that for electrically-driven vehicles mass actually drops to third on the list behind aerodynamics and electrical loads with rolling resistance coming in fourth."
 

·
Senior Member
Joined
·
3,689 Posts
I'm for making the tank smaller. Less space, weight, cost and a better turnover of little-used gas. Besides, who needs the 600 mile range? People say that today's cars have 600 mile + range. That may(is) be true but they use a lot more gas during the week than the Volt will. I think they should size the tank for the average highway driving time between bathroom breaks. :) I don't know about you marathon drivers but I'm good for about 4 hours at a time max. After driving 4 hours I like to stretch my legs. So, in my example in 4 hours at 70 miles per hour I get a tank size of 280 miles of needed range! Heck, that 400 mile range is looking good to me. :) I know several factors determine the range but I think for a plug-in hybrid vehicle the tank sizes can be significantly smaller.
 

·
Registered
Joined
·
4,085 Posts
Several of the recent articles after last week's press junket mention that they have decided to reduce the tank as Jason mentions, but I recall reading they expect 400 miles range. They have been stating about 50mpg fuel economy in generator mode, which would mean about 7 gallons. They mentioned saving space, weight, and money but it may also have to do with stale gas. They have repeatedly mentioned this as a concern and the bigger the tank, the longer a full tank will last.

I haven't heard of nor can imagine issues with partially filling the tank but the engineers did seem to shutter at the thought of no gas. That could cause issues.
Oh yeah, stale gas would be a good reason, along with saving weight and energy lost through sloshing fuel (I know, its negligible). Looking at the latest wind tunnel design, reduced fuel tank, etc., this Volt is going to be a great vehicle. I am not sure why a 2 + 2 isn't a popular configuration, but I think a lot of people will still like it.
 

·
Registered
Joined
·
223 Posts
Is the relationship between weight and efficiency linear? If so, it seems that 50 pounds out of 3000 would make a significant (though small) difference, about 1.67%, i.e. 50/3000.

GM has placed 4 factors in order in regards to their effect on the Volt's range,

1) Aerodynamics
2) Power consumption by accessories (AC, radio, defroster, etc.)
3) Weight
4) Tire rolling resistance

I estimate an 8 gallon tank for the Volt. The weight of 8 gallons of gas is about 50 lbs. For the difference between 3000 lbs (no gas) and 3050 lbs (full tank), I bet you would be hard pressed, even in laboratory conditions, to tell the economy difference based on the added weight of the fuel.

Conclusions: Drive it with whatever amount of gas you want, the effect on negligible.
 

·
Registered
Joined
·
767 Posts
Is the relationship between weight and efficiency linear?
I believe that this has been discussed in other threads and the more important question is:
At what points in the vehicles operation is extra weight a significant factor ??
The answer is: accelerating and going up hill.
And with a hybrid, those times are when the battery typically takes most of the load and the extra weight helps
recover more energy with the regen.

A little extra weight makes virtually no difference when cruising on the flat and no significant difference overall.
 

·
Administrator
Joined
·
20,101 Posts
Is the relationship between weight and efficiency linear? If so, it seems that 50 pounds out of 3000 would make a significant (though small) difference, about 1.67%, i.e. 50/3000.
Once the car is rolling, I think the effect of 50lbs is likely negligible. So while it will have some very, very small affect on battery range in stop and go traffic, it likely has almost zero effect while cruising. Since I use some gas every day, I treat my Volt gas tank like any other: fill it when it's almost empty, drive it untill it's almost empty again. Repeat.
 

·
Registered
Joined
·
5,188 Posts
Reducing the size of the tank is a BAD idea. The difference between an empty 10 gallon tank vs an empty 8 gallon tank is almost nothing. Nobody is forcing you to fill it. If anything... the current 350 mile range is too short for my needs. When I need to drive cross country I want a tank that can get me to 400-500 miles. The current 10 gallon tank is almost too small in my opinion. I hope they don't maker it any smaller!
 

·
Administrator
Joined
·
20,101 Posts
That was my first thought, prior to "doing the math." Math can be a dangerous tool if not handled properly! :)
For EVs, mass is still more critical for acceleration times than range loss. All things equal, aero affects range much more, which is why I'm keeping my longer front air dam and the standard side view mirrors. :)

According to GM engineers, aerodynamic factors matter more than mass, especially in an electric vehicle with regenerative braking.

In an electric-powered vehicle mass is secondary, according to Weber, even with a weight difference of 400 pounds. In the city, an all-aluminum Volt gets about 43 miles on a single battery charge, yet a 400-pound heavier vehicle would get 41 miles per charge. “There’s even less sensitivity on the highway side,” explains Weber. “It is 40 miles and 39 miles, just to illustrate.
http://www.greenfuelsforecast.com/ArticleDetails.php?articleID=491

This would mean a full gas tank @50 lbs decreases the city range by 2/10ths of a mile (or 1,056 feet) per full battery compared to a 1/4 filled tank. Halve that for the highway and you are at .1 miles (528 feet) range loss. I factor in the added insurance a full tank provides against things like storm's knocking out power and am fine taking a driving distance hit that's the length of my driveway. Tesla also has a graph showing that at highway speeds it's more about drive train losses. Range loss attributable to mass is insignificant. http://www.teslamotors.com/blog/roadster-efficiency-and-range

Of course that driving difference decrease over time as the tank is drawn down.

Part of the reason the extra weight doesn't have more impact is the Volt has regen. If you are not a jack rabbit at stop lights, much (about 65% maybe more) of the energy used to accelerate the extra weight is recovered when you decelerate to a stop.
 

·
Registered
Joined
·
130 Posts
To quote Steverino, "If you are not a jack rabbit at stop lights, much (about 65% maybe more) of the energy used to accelerate the extra weight is recovered when you decelerate to a stop."

Where did you get the 65% number? I drive mostly in L and use the brakes when needed, usually just a little in the last 2 or 3 car lengths behind the car.
 

·
Registered
Joined
·
827 Posts
Once the car is rolling, I think the effect of 50lbs is likely negligible. So while it will have some very, very small affect on battery range in stop and go traffic, it likely has almost zero effect while cruising.
In real world conditions, i can somewhat attest to that. During the week it's just me (work) and i get 52 miles on average/day of driving. On weekends, with wife and two kids (220lbs total,) but different traffic conditions i get 50 miles on average/day of driving -- and A/C is blasting more in this scenario. With conditions being equal, i probably could get the same mileage, or easily sway it one way or another. Driving behaviour certainly would have more effect that weight in these scenarios.

When I need to drive cross country I want a tank that can get me to 400-500 miles. The current 10 gallon tank is almost too small in my opinion.
Man, you must have a big bladder, too! :D
 

·
Administrator
Joined
·
20,101 Posts
1 - 17 of 17 Posts
Top