I've been getting around 20MPG on my Subi Outback ('97). After reading an article on increasing your mileage I tried driving 55 at all times where the speed limit was 55 or higher. Drove my girlfriend nuts, but I wanted to see what would happen to the mileage. Well, my MPG went from 20 to 27, and I used the AC a lot during that time. The car is also loaded with crap for work, and I removed the cross members from the roof rack. Tire pressure was
32 all the way around.
Depending on where I go I doubt I'll be driving that slow all the time, but at least I know my car is capable of much greater mileage than I've been getting. I think the article said that 45 mph got the maximum mileage.
45 mph might still get some folks seriously irritated at you, but here in SoCal, people overall have definitely slowed down since the gas pumps started reading $4/gal and more. There are a LOT fewer cars on the road most of the time, too, so it's not so hard to play around w/ varying speeds. It wasn't my Subie, but on three recent trips, holding to 60 in a vehicle that's turned in just over 25 mpg/avg for 100k miles, the average for the trips was 26.9-27.7, w/ a high tank on the last one of
33 mpg. Slowing down can certainly save some gas... I read an article in the paper yesterday that traffic fatalities have dropped something like
9% in the US as folks slow down, too.
I drive the speed limit now and try not to exceed it and am getting better mileage. Most of my driving is local, suburban and I cut back on rapid acceleration or deceleration. There is no sense accelerating to a line of traffic stopped at a light and it extends brake life.
"Frank" schreef in bericht news:U-mdnRSpu7dwlxbVnZ2dnUVZ_r snipped-for-privacy@comcast.com...
True, but it makes sense to accelerate at 3/4 of full throttle, because if you are too easy on the throttle, the pistons have to work against the throttle valve in your inlet manifold. Trick is open that valve as far as possible but not too wide, and get to cruisng speed as quick as possible. This can get you another 5% off.
Better yet: try to pace it to get there just as the light turns green again. 'Keep it rolling' is a very good fuel saver!
Gerard ( from Europe where fuel is REALLY expensive, close to $ 10,- / gallon ).
"Frank" schreef in bericht news:U-mdnRSpu7dwlxbVnZ2dnUVZ_r snipped-for-privacy@comcast.com...
True, but it makes sense to accelerate at 3/4 of full throttle, because if you are too easy on the throttle, the pistons have to work against the throttle valve in your inlet manifold. Trick is open that valve as far as possible but not too wide, and get to cruisng speed as quick as possible. This can get you another 5% off.
Better yet: try to pace it to get there just as the light turns green again. 'Keep it rolling' is a very good fuel saver!
Gerard ( from Europe where fuel is close to $ 10,- / gallon ).
Yeah, I've been doing that since the beginning of the year up here too. It's amazing how such a simple behaviour change results in such a huge mileage improvement. We've been told about slowing down since the
1970's, and it finally took $4+ gas to get us to obey it.
Up here in Canada there was a report that the local police forces are definitely noticing everybody has slowed down, and fewer tickets are being issued all across the nation.
Yeah. Most cars are geared for a balance of city and highway where highway speeds are considered 65-70 MPH (100-110 KPH). Hence, their most efficient speed is 70-80 KPH (45-50 MPH). That's where you will get the best gas mileage. Because air is a fluid and the amount of power required to increase speed is a square of the speed, there is a huge drop in gas mileage from 50-70 MPH.
I usually avoid the huge drop in gas mileage by shifting into 5th gear. Driving at 45 to 50 in most cars is not very feasible in fifth gear on highway that is not perfectly flat. The laws of fluid motion not withstanding, the last time I was able to accurately test any vehicle was on many trips between LA and Portland 30 years ago. I found my Peugeot which could hardly be driven at 55 in 5th gear got about the same mileage at 80 mph as at 55 mph. Driving at 70mph got me the best mileage, though at that time that was well over the speed limit. Could have been something about the shoebox dynamics of the styling. Except for the very newest crop of cars, most people could improve their mileage by simply reverting to vehicles made before the early nineties.
Most of us who are "slowing down" do stick to the right. Now, if you can just persuade those who DON'T want to slow down that passing is done "ON THE LEFT" (in the US and Canada ;)) we'll all be happier. AND safer.
Saw a good case of "Stupidity kills" a week or so ago when some fool thought he'd pass, on the right, at a high rate of speed, up a steep hill. Rear bumper of the 18-wheeler he hit pretty much took the whole top of the car off. Dunno if they pulled the body out of the car in one or two pieces...
With a 97 Impreza being the newest car I've owned, I can't refute your first statement, but I can guarantee that with the 11 year old subie, it would have been miserable trying to keep going at 35 mph in 5th. My 90 prizm/corolla always got 40mpg in non-ethanol months which is something I haven't heard repeated in the newer models. Hearsay was that some change in the mid-nineties dropped mileage a bit on most cars.
Some of this stuff seems like a case of the dumbing down of drivers and a lot of the people involved w/ the automotive industry. As Tony Hwang mentioned elsewhere in this thread, there's an "optimum" range for an internal combustion engine to produce the greatest power and torque per unit of fuel consumed. It's an rpm thing, not a vehicle speed thing.
So, while engines are more efficient than they were 20, 40 or 60 years ago, they still have to be run within whatever range they're designed for. Can't say I know of any small to medium sized cars where 35 mph should be done in much past 3rd gear. And from personal experiments, one often gets better mileage at a given vehicle speed by keeping engine revs up.
Now if I could just convince the guys who designed the "brain" behind the one auto I own of that fact, instead of the trans constantly "hunting" from 35-40 mph and up, trying to decide whether it should be in 3rd, 4th or 5th! Doesn't save any gas, does tear up transmissions. Oh, well...
I don't disagree with either of you. But, you're right; it is an RPM thing. Whether a car can optimally travel at low speed is a gearing thing. Part of the reason is left over from the double-nickel days; there was no reason to make a car more efficient at high speed when it isn't legal to drive them at high speed. And since the posted speed limit in North America is 80 MPH or less, that is what they have done. At 80 KPH (45 MPH), a small amount of the engine's available power is used to overcome drag. By 100 KPH (64 MPH) the majority of the car's power is used to overcome drag. By 75 MPH, a very high percentage is used to overcome drag; air acts like any fluid and any linear increase in speed requires and exponential power increase.
The optimum speed for the best gas mileage is the mimimum speed the car can go in high gear without the engine chugging; which for most North American cars is around 35-40 MPH; which, surprisingly enough, is the average speed a driver in North Amercan does over a long period of time. That's why most of the EPA highway tests are done at those speeds as an average.
In Europe, cars are geared differently (even if they are the same models available in North America) since the speed limits are substantially higher, and there are places where there are none at all.
The optimum engine speed for fuel economy is the maximum torque RPM. That said,today's engines are VERY flexible that way. Maximum torque goes from something like 1800 to 3000 rpm on some current engines. My 2003 PT cruiser is not one of those - max torque is at 4000 RPM and max HP at 5600. NO WAY that vehicle will be run at 4000 RPM cruise The 2.5 liter duratec in my wife's Mystique produces the same peak torque at 4200 rpm - but the torque curve is a lot fatter with the variable intake geometry.
But it's perfectly legal, last time I read the Motor Vehicle Act, to pass on the right. If it was possible to pass on the right, and you're in the left-hand-lane, especially if you're in a truck with poor visibility around you, dude.. I feel nothing but sympathy for that poor driver. Consider the possibility that he was speeding for a reason: how do we know if his pregnant wife was or wasn't just rushed to hospital and he was trying to get to her? How do we know whether his son was in trouble and called for help?
In many cases I've seen, the people who crash when they speed tend not to have a lot of experience speeding, in part because the tax-collectors, er sorry cops, are so draconian on speeders. Then one day they need to speed to save a life, or prevent harm to family, and they end up making mistakes like the one you saw.
It's not always stupidity: dude, you don't leave the scene of an accident you witnessed. We need to stop to try to help! We need to do something when we see these sorts of horrible tragedies and not just think people deserve their fate: dude, nobody deserves to die.
Our mentality needs a shift: consider what would've happened if someone witnessed us having a near-fatal accident and shrugged their shoulders and then took off and left us there to bleed.
People look at the STi I drive, and I know for a fact they're rooting for me to crash. They deliberately cut me off, they close gaps when I try to lane change, they speed up (regularly well past the speed limit) to prevent me from merging in front of them (though I have the right-of-way when my lane ends,) and the part that tells me they want me to crash: they'll pull these stunts in times when, if I don't merge successfully, I'll drive off a cliff or hit parked cars.
The mentality is to claw-back-your-neighbour, born of hate and spite and maybe jealousy, and we really need to work to stop it, man. So what if someone speeds? How many accidents are caused by speeding and speeding alone? Now, compare those numbers to alcohol-related incidents, or drug-related. Or, compare them to mechanical failure.
Come on, people: crashes are always a tragedy, no matter what the cause. Let's treat them as such.
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