Posted by Bruce Richmond on January 16, 2010, 3:05 am
> After 45mph - when driving at a constant speed 50% of all the
> energy expended by a motor vehicle is used to overcome wind
> resistance. Your Prius is about 3200lbs so adding 800lbs of
> payload is is adding about 25% of extra weight to the Prius
> which should be within its designed performance.
You're missing the point. The additional weight requires almost no
additional power to keep moving at a constant speed, especially with
the tires pumped up to 45 psi.
>I personally
> go about 55mpg on a 2006 Prius on a long trip from Washington
> DC to Grand Rapids Michigan - my mileage would have
> been better if I had not sped up to 70mph in Michigan but
> almost all the vehicles on the super highway in Michigan
> are going at 70 to 80 mph there. However, while I was in
> Maryland, Pennsylvania, and Ohio I drove about 55 mph
> (I believe I could have gotten 60mph if I stuck to 55mph
> all the way) .
The mileage my Prius gets goes down drasticly as speed goes up. At 65
it gets about 47 mpg. At 75 it gets 38. Really suprised me that it
dropped off that fast. Saw some charts and it's not just that the
power required is higher, the engine drops out of its most efficient
operating range.
> Question: Does a motorcycle wind cowls help with either
> performance or fuel efficiency? If so how much?
Depends on the fairing. Touring fairings in particular are intended
to provide protection more than efficiency. Same with sport bike
fairings to some extent, and to counteract lift. To get a low Cd the
front wheel needs to be enclosed as was done in old "dust bin"
fairings. But those were banned from racing in part due to bad
effects from crosswinds. The sportbike crowd wants their bikes to
look like race bikes, so... The biggest problem for streamlining a
bike isn't at the front, it is closing the wake behind the rider.
> > > > So a fat guy has no gas economy on a scooter.
> > > > LOL
> > > > Neo wrote:
> > > > It's a matter of power to weight ratio, a 240lb scooter with
> > > > 10 HP is 24 lb per horsepower, my Saturn weights 2400lbs and
> > > > has 100 HP, the same power to weight ratio. In town a scooter would have
> > > > no problem keeping up with traffic, few people are going to use one for
> > > > anything other than short trips anyway and off major highways.
> > > > Which at that weight is likely no safer than a scooter or motorcycle ;~)
> > > I agree that a scooter is would have no problem in a
> > > urban driving environment - it would also have a parking
> > > and manueverablity advantage over the larger cars and
> > > trucks as well. Its disadvantage would be protection
> > > from the weather and safety. Certain metro-only cars
> > > like ones made in Inda or China (e.g. Reva, Flybo)
> > > might be a better fit than a scooter if weather or cargo
> > > capacity was a primary need/mission. If cargo capacity
> > > is not a problem and the operator is physically fit -
> > > a regular bicycle might be a better fit in an urban
> > > environment than a scooter.
> > > With a ICE vehicle the power transfer efficency is not just
> > > a matter of power to weight ratio but also the ICE transmission
> > > efficiency (power to transfer ratio). for a particular speed which
> > > is why very skilled drivers can optimize energy efficiency
> > > with a manual transmission and why a properly tuned
> > > transmissions with additional drive gears (or a CVT) has
> > > better fuel efficiency than the a vehicle with less drive
> > > gears. Each vehicle is designed with a maximum payload
> > > in addition to its curb weight which the ICE is designed
> > > to efficiently handle - that maximum payload includes the
> > > weight of the operator/driver - so a 400 lb scooter operator
> > > take more fuel to move than a 100 lb scooter operater
> > > (with no other payload) - not to mention that a skinny
> > > operator might have less wind resistance at higher speed.
> > Your ideas on the effects of weight on fuel economy need some
> > revision. Driving down the highway at near constant speed added
> > weight has almost no effect on fuel mileage. It does take more fuel
> > to accelerate, but much of that energy can be recovered by a hybrid
> > with regenerative braking.
> > Recently I purchased two ton of coal from a store near where I work,
> > 11 miles from home. Rather than pay them to deliver it to my home, or
> > borrow a truck and make a special trip myself, I just loaded 800 lbs
> > into my car each day for five days. That way I figured the only cost
> > for transport would be the additional fuel used for my trip home as
> > compared to not having the coal in the car. The car happen to be a
> > 2001 Prius that has a readout for instantaneous and average fuel
> > milage. It also has regenerative braking. Turned out that I got 52
> > mpg, about the same as I get without the extra 800 lbs. The main
> > difference was that acceleration was sluggish due to the extra
> > weight. The trip was mostly on level roads with a few gentle hills.
> >http://nepacrossroads.com/download/file.php?id=16495&mode=view
> > Before anyone gives me grief about hauling 800 lbs of coal in the car,
> > just think of it as four two hundred pound passengers :)
> > The other day I tried keeping the speed down around 40 to 50 mph for a
> > 40 mile trip over secondary roads. The Prius averaged 60 mpg. I have
> > several motorcycles. The one that gets the best mileage is a 1981 GPZ
> > 550 Kawasaki. At 55 mph it gets 55 mpg. This 1972 BMW 750 only gets
> > about 15 mpg
> >http://nepacrossroads.com/download/file.php?id=16495&mode=view
> > But somehow that doesn't bother me a bit :) That's me driving 66. We
> > took 3rd in the championship last year.
> > > Once the kinetic energy of the ICE moves the tires - the
> > > vehicle has wind resistance and the tire's friction/rolling
> > > resistance of the tires to deal with. The wind resistance
> > > is a function of wind surface and that wind's surface
> > > drag coefficient. Most scooters and motorcycles have
> > > very little wind surface but a high wind surface drag
> > > coefficient. Most four wheeled vehicles like trucks
> > > have a much larger wind surface but a lower wind
> > > surface drag coefficient. While one passenger/driver
> > > motorize bikes have the potential for the lowest overall
> > > wind resistance and probably the highest fuel efficiency
> > > that commercial potential has not been realized.- Hide quoted text -
> > - Show quoted text -- Hide quoted text -
> > - Show quoted text -- Hide quoted text -
> - Show quoted text -
Posted by Neo on January 16, 2010, 10:06 am
> > After 45mph - when driving at a constant speed 50% of all the
> > energy expended by a motor vehicle is used to overcome wind
> > resistance. Your Prius is about 3200lbs so adding 800lbs of
> > payload is is adding about 25% of extra weight to the Prius
> > which should be within its designed performance.
> You're missing the point. The additional weight requires almost no
> additional power to keep moving at a constant speed, especially with
> the tires pumped up to 45 psi.
I agree once you get up to about 55 mph and start moving
at a constant speed, the energy required to move an
the extra 800 pounds should be barely noticable on
Prius which is rated to carry over slightly over 800 lbs of payload.
http://autos.aol.com/cars-Toyota-Prius-2010/specs
However, going significantly beyond that (e.g. 1000lbs of coal)
may pose a risk of additional wear on the power train and
the suspension. I'm sure that the Toyota's engineers have
designed the Prius to handle more than the published specs
- but I wouldn't risk it...
> The mileage my Prius gets goes down drasticly as speed goes up. At 65
> it gets about 47 mpg. At 75 it gets 38. Really suprised me that it
> dropped off that fast. Saw some charts and it's not just that the
> power required is higher, the engine drops out of its most efficient
> operating range.
My experience with the 2006 Prius and
2008 Prius ( at the manufacturer's recommended
tire psi) supports your observations -
very speeds kills the Prius mpg advantage.
Drivers who yearn for very high speeds
and very high mileage need to look elsewhere. .
Also in extremely low temperatures the Prius
mileage drops from about 50 mpg to about 40 mpg.
One hypermiler trick that I read but have
not confirmed yet to raise the Prius
mpg up in cold weather is to block the
air flow to the ICE ( so the ICE heats up
faster and loses less heat during operations).
This technique however is used by the
local diesel yellow school buses and
eighteen wheeler tractor trailer during
the winter. So during the winter in the
washington DC area, many diesel vehicles
can be seen with their front airtakes
covered with cardboard and duct tape. (9_9)
> > Question: Does a motorcycle wind cowls help with either
> > performance or fuel efficiency? If so how much?
> Depends on the fairing. Touring fairings in particular are intended
> to provide protection more than efficiency. Same with sport bike
> fairings to some extent, and to counteract lift. To get a low Cd the
> front wheel needs to be enclosed as was done in old "dust bin"
> fairings. But those were banned from racing in part due to bad
> effects from crosswinds. The sportbike crowd wants their bikes to
> look like race bikes, so... The biggest problem for streamlining a
> bike isn't at the front, it is closing the wake behind the rider.
Your explanation explains the Aptera 2e design ...
Thank you very much! :-)
Posted by Bruce Richmond on January 17, 2010, 7:42 am
> > > After 45mph - when driving at a constant speed 50% of all the
> > > energy expended by a motor vehicle is used to overcome wind
> > > resistance. Your Prius is about 3200lbs so adding 800lbs of
> > > payload is is adding about 25% of extra weight to the Prius
> > > which should be within its designed performance.
> > You're missing the point. The additional weight requires almost no
> > additional power to keep moving at a constant speed, especially with
> > the tires pumped up to 45 psi.
> I agree once you get up to about 55 mph and start moving
> at a constant speed, the energy required to move an
> the extra 800 pounds should be barely noticable on
> Prius which is rated to carry over slightly over 800 lbs of payload.
Why do you keep trying to put limiting qualifieres in that don't
matter in the real world? You get the same milage at a steady 20 mph
with or without the added weight. You get the same mileage at a
steady 70 mph with or without the added weight. And since you get the
same mileage at a steady speed with or without the maximum rated load
it tells you that you would get the same mileage for any load less
than the maximum, and probably over it. And physics says this is true
for any car, not just the Prius. The place where the Prius might gain
some advantage is when the speed is not steady due to it's ability to
recover some of the energy used to accelerate when it slows.
> http://autos.aol.com/cars-Toyota-Prius-2010/specs
> However, going significantly beyond that (e.g. 1000lbs of coal)
> may pose a risk of additional wear on the power train and
> the suspension. I'm sure that the Toyota's engineers have
> designed the Prius to handle more than the published specs
> - but I wouldn't risk it...
The suspension would be a concern but not the power train. If it is
getting the same mileage then you are not working it any harder.
> > The mileage my Prius gets goes down drasticly as speed goes up. At 65
> > it gets about 47 mpg. At 75 it gets 38. Really suprised me that it
> > dropped off that fast. Saw some charts and it's not just that the
> > power required is higher, the engine drops out of its most efficient
> > operating range.
> My experience with the 2006 Prius and
> 2008 Prius ( at the manufacturer's recommended
> tire psi) supports your observations -
> very speeds kills the Prius mpg advantage.
> Drivers who yearn for very high speeds
> and very high mileage need to look elsewhere. .
> Also in extremely low temperatures the Prius
> mileage drops from about 50 mpg to about 40 mpg.
I haven't noticed much difference due to temps after it has warmed up
but there is a big difference during the warm up period. When the
engine is cold the fuel injection squirts in more fuel and raises the
idle speed. It also will not let the engine shut down till the
battery has been charged and the coolent is up to temp. It does make
a bit of difference if you turn the heater off. The engine will come
on any time the engine coolent drops below some limit just to bring it
back up to temp.
> One hypermiler trick that I read but have
> not confirmed yet to raise the Prius
> mpg up in cold weather is to block the
> air flow to the ICE ( so the ICE heats up
> faster and loses less heat during operations).
> This technique however is used by the
> local diesel yellow school buses and
> eighteen wheeler tractor trailer during
> the winter. So during the winter in the
> washington DC area, many diesel vehicles
> can be seen with their front airtakes
> covered with cardboard and duct tape. (9_9)
> > > Question: Does a motorcycle wind cowls help with either
> > > performance or fuel efficiency? If so how much?
> > Depends on the fairing. Touring fairings in particular are intended
> > to provide protection more than efficiency. Same with sport bike
> > fairings to some extent, and to counteract lift. To get a low Cd the
> > front wheel needs to be enclosed as was done in old "dust bin"
> > fairings. But those were banned from racing in part due to bad
> > effects from crosswinds. The sportbike crowd wants their bikes to
> > look like race bikes, so... The biggest problem for streamlining a
> > bike isn't at the front, it is closing the wake behind the rider.
> Your explanation explains the Aptera 2e design ...
> Thank you very much! :-)
Posted by Josepi on January 17, 2010, 11:34 am
Tires and drive mechanisms (suspension angles) add a slight increase in
friction with weight increase. I am not sure how signifiacnt this would be.
Wind resistance doesn't change.
> > > After 45mph - when driving at a constant speed 50% of all the
> > > energy expended by a motor vehicle is used to overcome wind
> > > resistance. Your Prius is about 3200lbs so adding 800lbs of
> > > payload is is adding about 25% of extra weight to the Prius
> > > which should be within its designed performance.
> > You're missing the point. The additional weight requires almost no
> > additional power to keep moving at a constant speed, especially with
> > the tires pumped up to 45 psi.
> I agree once you get up to about 55 mph and start moving
> at a constant speed, the energy required to move an
> the extra 800 pounds should be barely noticable on
> Prius which is rated to carry over slightly over 800 lbs of payload.
Why do you keep trying to put limiting qualifieres in that don't
matter in the real world? You get the same milage at a steady 20 mph
with or without the added weight. You get the same mileage at a
steady 70 mph with or without the added weight. And since you get the
same mileage at a steady speed with or without the maximum rated load
it tells you that you would get the same mileage for any load less
than the maximum, and probably over it. And physics says this is true
for any car, not just the Prius. The place where the Prius might gain
some advantage is when the speed is not steady due to it's ability to
recover some of the energy used to accelerate when it slows.
> http://autos.aol.com/cars-Toyota-Prius-2010/specs
> However, going significantly beyond that (e.g. 1000lbs of coal)
> may pose a risk of additional wear on the power train and
> the suspension. I'm sure that the Toyota's engineers have
> designed the Prius to handle more than the published specs
> - but I wouldn't risk it...
The suspension would be a concern but not the power train. If it is
getting the same mileage then you are not working it any harder.
> > The mileage my Prius gets goes down drasticly as speed goes up. At 65
> > it gets about 47 mpg. At 75 it gets 38. Really suprised me that it
> > dropped off that fast. Saw some charts and it's not just that the
> > power required is higher, the engine drops out of its most efficient
> > operating range.
> My experience with the 2006 Prius and
> 2008 Prius ( at the manufacturer's recommended
> tire psi) supports your observations -
> very speeds kills the Prius mpg advantage.
> Drivers who yearn for very high speeds
> and very high mileage need to look elsewhere. .
> Also in extremely low temperatures the Prius
> mileage drops from about 50 mpg to about 40 mpg.
I haven't noticed much difference due to temps after it has warmed up
but there is a big difference during the warm up period. When the
engine is cold the fuel injection squirts in more fuel and raises the
idle speed. It also will not let the engine shut down till the
battery has been charged and the coolent is up to temp. It does make
a bit of difference if you turn the heater off. The engine will come
on any time the engine coolent drops below some limit just to bring it
back up to temp.
> One hypermiler trick that I read but have
> not confirmed yet to raise the Prius
> mpg up in cold weather is to block the
> air flow to the ICE ( so the ICE heats up
> faster and loses less heat during operations).
> This technique however is used by the
> local diesel yellow school buses and
> eighteen wheeler tractor trailer during
> the winter. So during the winter in the
> washington DC area, many diesel vehicles
> can be seen with their front airtakes
> covered with cardboard and duct tape. (9_9)
> > > Question: Does a motorcycle wind cowls help with either
> > > performance or fuel efficiency? If so how much?
> > Depends on the fairing. Touring fairings in particular are intended
> > to provide protection more than efficiency. Same with sport bike
> > fairings to some extent, and to counteract lift. To get a low Cd the
> > front wheel needs to be enclosed as was done in old "dust bin"
> > fairings. But those were banned from racing in part due to bad
> > effects from crosswinds. The sportbike crowd wants their bikes to
> > look like race bikes, so... The biggest problem for streamlining a
> > bike isn't at the front, it is closing the wake behind the rider.
> Your explanation explains the Aptera 2e design ...
> Thank you very much! :-)
Posted by Neo on January 17, 2010, 2:32 pm
> > > > After 45mph - when driving at a constant speed 50% of all the
> > > > energy expended by a motor vehicle is used to overcome wind
> > > > resistance. Your Prius is about 3200lbs so adding 800lbs of
> > > > payload is is adding about 25% of extra weight to the Prius
> > > > which should be within its designed performance.
> > > You're missing the point. The additional weight requires almost no
> > > additional power to keep moving at a constant speed, especially with
> > > the tires pumped up to 45 psi.
> > I agree once you get up to about 55 mph and start moving
> > at a constant speed, the energy required to move an
> > the extra 800 pounds should be barely noticable on
> > Prius which is rated to carry over slightly over 800 lbs of payload.
> Why do you keep trying to put limiting qualifieres in that don't
> matter in the real world? You get the same milage at a steady 20 mph
> with or without the added weight. You get the same mileage at a
> steady 70 mph with or without the added weight. And since you get the
> same mileage at a steady speed with or without the maximum rated load
> it tells you that you would get the same mileage for any load less
> than the maximum, and probably over it. And physics says this is true
> for any car, not just the Prius. The place where the Prius might gain
> some advantage is when the speed is not steady due to it's ability to
> recover some of the energy used to accelerate when it slows.
So far I haven't found any information about
how much additional payload (over the official
maximum payload specs ) that one can
safely put on the Prius in the real world
without destroying it. I'm sure the toyota engineers
have built in some level of tolerance to make
the Prius more reliable so that one can go
over the design limits in the real world by
a certain degree - but they're mums. When
I asked that question about two years ago
I got the same answer that I am essentially
writing now.
The Prius' optimum fuel efficiency is achieved when running
constantly at about 40-50 mph on a flat surface. The Prius
fuel efficiency should be the same at a fixed speed when
its payload is within its designed load (825 lbs). When the
payload is significantly over the designed limit ( Payload
is > 1000 lbs) - the added weight to the drive train and
the additional rolling friction resistance will most likely
cause some decrease in fuel efficiency even if it only
appears as a fractional increase in energy cost.
Officially Toyota says that the Prius regenerative
brakes recaptures 30% of the car's kinetic energy
but I've read claimed that Prius's brakes can
recaptures about 50% of the car's kinetic energy
when certain hypermiler techniques are used.
The more significant risk is screwing up your car
---------------------------------------------------------------------
When a car is burdened with payload over its
designed limits the greatest risk to the car's
future operational integrity is the deforming of
the cars suspension (springs, shock absorbers, struts)
wearing the brakes prematurely, and extra tire wear.
As stated in another post, the Prius drive train
( more specifically the CVT) may also fail or be
at risk if the payload goes over the engineered limits.
I know I sound like a kill joy - but I think the
Toyota Highlander Hybrid would be a better
choice if one needs to haul really heavy payloads
or tow anything.
> > Also in extremely low temperatures the Prius
> > mileage drops from about 50 mpg to about 40 mpg.
> I haven't noticed much difference due to temps after it has warmed up
> but there is a big difference during the warm up period. When the
> engine is cold the fuel injection squirts in more fuel and raises the
> idle speed. It also will not let the engine shut down till the
> battery has been charged and the coolent is up to temp. It does make
> a bit of difference if you turn the heater off. The engine will come
> on any time the engine coolent drops below some limit just to bring it
> back up to temp.
My sister who lives close to the Canadian border
just purchased a 2010 Prius type III a few weeks
ago. It pretty cold there now and she reported to
me she is getting overall about 40 mpg in a mix
of both city and highway driving.
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> energy expended by a motor vehicle is used to overcome wind
> resistance. Your Prius is about 3200lbs so adding 800lbs of
> payload is is adding about 25% of extra weight to the Prius
> which should be within its designed performance.