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Fuel Efficiency and Slow Driving?
vile8 writes "With the high gas prices and ongoing gas gouging in my hometown many people are trying to find a reasonable way to save gas. One of the things I've noticed is people driving exceptionally slow, 30mph in 45mph zones, etc. So I had to take a quick look and find out if driving slow is helpful in getting better mileage. I know horsepower increases substantially with wind resistance, but with charts like this one from truckandbarter.com it appears mileage is actually about the same between 27mph and 58mph or so. So I'm curious what all the drivers out there with the cool efficiency computers are getting ... of specific interest would be the hemis with MDS; how do those do with the cylinder shutoff mode at different speeds?" Related: are there any practical hypermiling techniques that you've found for people not ready to purchase a new car, nor give up driving generally?
Make those fuel consumption displays mandatory.
Most cars these days know their consumption - it's one of the first things they look at when they connect the laptop to the engine when you go for a service.
Make the display mandatory, make it large, and put it in a prominent place. It'll do wonders for everybody's fuel consumption.
No sig today...
There are sweet spots for driving which is usually specific to the type of vehicle, the gearing, etc. so, to an extent, I'm sure the faster you go the better MPG you will see. But for my car, Mitsubishi Spyder, they recommend shifting into 6th at about 50mph. So basically my interstate driving is all in the top gear by far. At 70-75mph driving on WV interstate highways I get about 20-21 MPG. If I just drop my speed to 65mph everywhere I go during a tank of gas I can reach 24 MPG. I've consistently seen those results out of at least the last 3 or 4 tanks of gas over the last couple months. If I take a US Route (speed limit 55) for 90 minutes to visit my parents my MPG goes up even more for that period of time because I'm going even slower than my usual 65-75 mph. I don't drive too much slower than the posted speed limit (5mph as I state above) because I don't want to feel like I'm crawling but just dropping 5 mph makes a noticeable difference in the range I can achieve with my tank (17.7 gallons). YMMV.
this nation, under God, shall have a new birth of freedom. -- Lincoln, Gettysburg Address
I've gotten lazy with this. When I know a stop is coming up, I put the car in neutral and let it coast. After a while, my clutch leg starts to hurt, so it's easier this way. People may think I'm weird, but I do it up to a mile away. The car coasts really well, so I'm usually not going any slower than I should be anyways. :)
Serious? Seriousness is well above my pay grade.
In a small, aerodynamic car, speed doesn't matter that much. (In a larger vehicle and especially trucks, with their poor aerodynamics, speeds above 60 do start to affect mileage more strongly.)
But how vigorously you accelerate can make a big difference. In the worst of the gas price spike I made a point of accelerating gently and shifting much earlier than usual, and found my mileage improved by 15%.
Your god may be dead, but mine aren't!
Yeah. There was an article in Readers Digest a few months ago about "hypermiling" or whatever, and it was a case study in "I'm the only person on the road". Incredibly arrogant and self-centered.
No folly is more costly than the folly of intolerant idealism. - Winston Churchill
Oh, for mod points. Most people (well, most men anyway) are competitive, and we like to beat our "high scores". Tachometers show us speed, clocks show us time, but neither of those contributes to efficiency. Adding a fuel economy display gives a better goal to beat.
If you were blocking sigs, you wouldn't have to read this.
Holding in your clutch a lot will stuff your throw-out race. That's really bad, because that'll lead to a clutch that you can't engage or disengage. Not having a clutch when you need it is really really bad.
Engine braking is good practice. Putting aside the cleverness of modern ECUs, most footbrakes fade with use as they heat up. Yes, even disc brakes; they're a heap better than drum, but they can still overheat very rapidly.
If you're coming down a very long, steep hill and you're not engine braking, your brakes will be much less effective by the time you reach the bottom.
Brakes are a safety device, not a speed control tool. You brake only when required. Your accelerator pedal and engine braking is what you use to control your vehicle's speed. If you need to use your brakes other than to come to a stop, you're pushing your car too damned hard, or you're too damned close to the guy in front of you. Back off.
Using the holy grail of OSes...
Foolish. All engines are designed to brake.
Brakes are a safety device; you need them for keeping the car stationary, bringing it to a stop from low speeds, to prevent emergency situations from occurring, and for use in an emergency situation itself.
You save them; you don't use them. If you use your brakes as a matter of course, to control your speed, then you won't have them when you need them, due to heat build-up. No, disc brakes won't save you - they're better than drum, but they still heat up and loose effectiveness. No, ABS won't save you, either. It still has nothing to play with if your brakes have heated up.
Which would you rather: a bit of fuel economy (dubious anyway), or a large funeral bill?
Using the holy grail of OSes...
While wind resistance scales with speed squared, the simple fact is that most of the energy wasted in a car is in stopping, not wind resistance. Normal driving around the city I can get 19-22 MPG, and I use smart braking like the parent discusses. Driving 65-75 MPH across states (where I am just GOING), I can get almost 35.
This is just another case where people don't realize (or care) that trying to maximize the performance of one part of the system (their commute) ends up diminishing the performance of the overall system.
Only a few people doing this slow driving will result in large numbers of other driver stuck waiting at more lights. Even worse, this kind of slow driving will result in some other drivers driving recklessly trying to get around the slow drivers. It won't take many crashes, injuries, and deaths to completely wipe out any savings made to the economy by a few people driving slowly (if only from traffic backups due to crashes).
Using these kinds of hypermiling techniques are just fine for an individual who doesn't have any regard for how their behavior impacts others.
I can confirm that in my Saturn, optimal highway fuel efficiency is 55 to 60mph. I've tested this quite extensively. If you follow hypermiling discussions, for most people, their experience is quite similar. If I drive my Saturn at 80mph, I get about 30mpg. If I drive at 55-60mph, I usually get just over 40mpg. On a good trip, if I combine it with shifting into neutral for downhill runs, follow large slow-moving vehicles (no, not tailgating; I always keep a safe distance), and so forth, I've gotten 45mpg out of it. This is repeatable and has been determined over dozens of documented fillups.
In city, I haven't been able to collect good data about whether my city hypermiling techniques are helping significantly or not because my partner does most of the city driving on the same vehicle, so it messes up my numbers. I don't do the dangerous things like shutting off the engine or doing breakneck turns, but I do accelerate slowly, look way ahead and take hills into account, coast to red lights, time lights, take turns at moderate speeds, and avoid roads with stop signs. Given that I use my brakes only a fraction as much, I *should* be getting significantly better mileage, but unfortunately, I have no way of knowing.
If I ever become wealthy and mad, I'll leave Companion Cubes on desert islands for shipwreck survivors.
Hypermiling isn't even remotely about slow driving. It is about accelerating at an optimal rate, cruising at an optimal rate, and carrying no more speed than necessary to get to the next known stop.
Pay special attention to that last one. Carrying no more speed than necessary to get to the next known stop. A hypermiler's behaviour isn't going to affect anyone. If they were all going to be stuck at the next red light, they were all going to be stuck at the next red light. If they were going to make the light, everyone can cruise at their optimal rate.
A hypermiler's behaviour only impacts how other drivers _think_ they are doing in terms of making good time to their destination. Such other drivers love to do things like see that a light is turning red and then _accelerate_ towards it because they want to be first in line. Or because it just feels good. Or whatever. But they'll be waiting at that exact same red light as everyone else, including the hypermilers.
Posts like yours place the blame here on the hypermilers, but the blame should reside elsewhere.
Sounds like you really don't know how cars work, then. Older mechanical fuel injection systems or carburetors CAN get better mileage with full-throttle acceleration (if you keep the RPM down using a manual transmission). The reason is the open throttle lets the engine breathe easier so it's not wasting energy drawing air past a restricted opening. BMW and others have experimented with eliminating the restrictive butterfly to improve economy, and of course one of the reasons diesels enjoy better economy is because they have no throttle butterfly.
So, yes, you can improve economy by keeping that throttle open and the RPM low -- as long as your computerized fuel injected engine doesn't perform WOT enrichment (or you disable that feature).
DRM 'manages access' in the same way that a prison 'manages freedom'
Exactly.
If you drive well, you don't use much the breaks. In fact, the ideal ride is one you don't use the breaks at all, save for full stops.
factor 966971: 966971
tylernt covers the "full throttle" component of this in another reply to your post.
I'm an Australian, and the son of an engineer who restores old vehicles for a living. We have British, Italian and Japanese vehicles. We have never owned an American vehicle.
The BMW data was almost certainly collected for their vehicles, which almost uniformly (at the time of the study) used straight 4 or straight 6 engines. 75% throttle would have been a rough figure arrived at for their own machines, I would imagine.
It is patently obvious that applying more throttle increases the amount of fuel used per second. However, the amount of fuel used is not a direct 1:1 to your acceleration.
The trick here is not that you use less fuel to reach your desired speed by accelerating harder. That's nonsense, and an incorrect understanding of the problem. Accelerating harder may well use more fuel to reach your desired speed. The trick is in how much time your spend at you desired speed, not accelerating.
If you do the calculus on this, you'll note that with the rapid acceleration model, you spend a far greater time at your desired target speed over the course of your journey. While at that speed, you are not accelerating. You will use more fuel accelerating quickly than accelerating slowly, per unit of time. However, your overall time spent not accelerating but simply maintaining speed more than compensates.
Using the holy grail of OSes...
Three reasons this is a bad idea. One, if you suddenly have to swerve to avoid something, you might miss the edge that the power steering would provide Two, you might need to suddenly apply engine power in some emergency situations, like if you hit black ice and start skidding. Three, if you accidentally turn the key too far back, you'll engage the steering wheel lock and won't be able to steer at all.
In short: really bad idea.
Four, if you need to stop suddenly, I hope you have strong legs. Those brakes don't work very well when your system isn't pressurized anymore.
Five, your cooling system may no longer be working, and if you are riding the edge of an overheat (considering you're driving far enough to consider killing the engine on coast) this may push you over the edge.
For large sets, this will be our guide even unto death, for the LORD will work for each type of data it is applied to...
Really? How many more miles does he expect to get on that engine before the repeated stress of starting it burns out the starter motor, at a minimum? Seriously, when the engine isn't running, the oil pump isn't running. When the oil pump isn't running, the oil runs down into the drain pan (especially when it's already hot). When you start a car, the cylinders are underlubricated until the oil pump gets things moving again. How many gallons of gas to you have to save to pay for a new engine, both in economic and ecological terms?
Also, keep the jerk in mind the next time you have a smoggy day. What did you think happened to all that unburned gas in the exhaust? Catalytic converters aren't magic, you know.
Dewey, what part of this looks like authorities should be involved?
Why the fuck is this modded as redundant? While it may be a case of "Yes, it's against the law, but..." it IS a safety issue. On several occasions I've had to get the hell out of the way quickly, and had I been coasting in neutral, I'd most likely be dead now.
I'd rather have a dead clutch than a dead me. Besides, with a knackered clutch, going up hills is MUCH more entertaining. Will you make it to the top? YOU JUST DON'T KNOW! It's like an extreme sport. Make it to the top of a particularly steep hill with a slipping clutch and you should really go buy a lottery ticket, as you're clearly one lucky SOB.
So, yes, you can improve economy by keeping that throttle open and the RPM low -- as long as your computerized fuel injected engine doesn't perform WOT enrichment (or you disable that feature).
Since your "exception" is basically 90%+ of cars on the road, you are actually agreeing with the gp?
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