| Re: [GMCnet] A little common sense from the adults? non GMC [message #99847] |
Wed, 15 September 2010 06:40  |
Gary Casey
Messages: 448
Registered: September 2009
Karma: 0
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Senior Member |
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Sorry, but there is no way that changing inflation pressure can account for a
20% gas mileage improvement. It depends on the driving conditions, but for
highway-type driving in a small car the losses are roughly 50% aero drag, 30%
engine friction and 20% rolling resistance. Of the rolling resistance more than
half is probably due to tire losses. But modern radial tires don't change
resistance a lot with pressure, as did the old bias-ply tires, and the
recommended tire pressures are not far from optimum anyway. I would expect that
raising pressure will only get you 1 or 2 percent improvement in fuel economy
and most of that will be in the first few psi of increase. Going much higher in
pressure will adversely affect the ride and safety (lower highway stability).
To improve fuel economy, slow down and change your driving habits. If you want
to get 1 percent by modifying the car, remove the side mirrors :-). Another 1
percent can be had by going to a 5W-20 synthetic oil from a 10W-30 standard oil.
Then make sure there is no ethanol in the fuel... I tell people that want to
improve gas mileage to avoid stepping on the gas OR the brake. New fuel
injected cars are different than old cars. They don't burn any gas while
coasting - and the BSFC is better at full throttle than at part throttle. Yup;
"jackrabbit starts" and hard braking don't hurt fuel economy. Keep the
converter clutch on as much as possible. Only drive in the summer. Move to
higher elevation.
Just some food for thought,
Gary Casey
I run our passenger cars at max sidewall psi. It gives a little harsher
ride, but I pick up quite a bit of mileage 20-25%. My 04 Sienna minivan is
getting 25-30mpg on trips, when previously it was only getting 21mpg and I
don't even notice the ride change. My Edge previously only got 18mpg, now
it's getting 22mpg, it does ride like a pickup now... YMMV.
On Tue, Sep 14, 2010 at 9:24 PM, dave silva <gmc@davesilva.com> wrote:
>
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| Re: [GMCnet] A little common sense from the adults? non GMC [message #99848 is a reply to message #99847] |
Wed, 15 September 2010 06:58  |
hertfordnc
Messages: 1164
Registered: September 2009
Location: East NC
Karma: 0
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Senior Member |
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Gary,
I think the truth is somewhere in the middle. Hybrid driving is a bit different (I can say this after only four days)
It's partially about efficient propulsion but it's also about efficient energy recovery.
With the tires really hard you coast a lot further and recover a lot more energy.
The real time MPG indicator in the Civic Hybrid is accurate to about 2% so you really get to see what works in real time.
Because of the energy recovery, anything you do to improve rolling efficiency has at least twice the affect.
But like i said, i am not all that interested in triple digit mileage, i don't lose sleep over my carbon footprint and I am definitely not giving up my AC to save a few drops of petrol.
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