Hybrid Car – More Fun with Less Gas

70 mpg - Page 14

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Posted by Bruce Richmond on January 16, 2010, 3:05 am
 



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.


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.


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.



Posted by Neo on January 16, 2010, 10:06 am
 



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...




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)



Your explanation explains the Aptera 2e design ...
Thank you very much! :-)


Posted by Bruce Richmond on January 17, 2010, 7:42 am
 


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.


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.


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.



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.



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.


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.


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.



Posted by Neo on January 17, 2010, 2:32 pm
 


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.



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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---> Re: 70 mpg Jim Wilkins01-03-2010
| |--> Re: 70 mpg Jim Wilkins01-03-2010
| | `--> Re: 70 mpg Bruce Richmond01-16-2010
| |--> Re: 70 mpg Bruce Richmond01-17-2010
| |     ---> Re: 70 mpg Alistair Gunn01-19-2010
| |       `--> Re: 70 mpg Daniel who want...01-19-2010
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