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Best way to accelerate to save gas?
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Is it better to accelerate slowly until I reach the speed I need to, or push the pedal down further and accelerate quicker?
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EDIT: I've never really heard whether it's good or bad, but I'd imagine it might create some extra wear and tear doing so... but that happens over time when you shift anyway...
as for accelerating, your RPMs is the main determinant in wasting gas. If you push the pedal to the floor you are wasting a lot of gas. However no one wants to follow an old grandpa driver who can't find the pedal, anywhere from 2-3k rpms is good for accelerating, to maximize saving gas.
When you're on the highway, stick to the right lane(s), find a tractor trailer and leave about a 2 second gap between you and it, and you can "draft" in his air wake just like nascar drivers do, you'll save a TON of gas that way but it's super dangerous and illegal in some areas.
If you want to be sure though - make sure you can see his rearview mirrors. If you can't you are in his blindspot.
At 30, 40 or even 55 sure, at 70 or 80 mph though, it's more like 3-5.
So yes, accelerating quickly will generally use more fuel. There's some funny issues with cars and gearing that'll fluctuate the optimum acceleration and speed fuel consumptions of a car but in general, hammering the accelerator and driving faster will use up more fuel.
Your cars handbook should quote an ideal speed/gear for fuel consumption (for example, I think my cars optimum fuel consumption is travelling at 55mph in 5th gear IIRC). Not sure if they quote optimum acceleration/gears though.
What are you talking about? I don't recall offhand what the follow distance is in [insert state here], but if you are describing it in time, then it won't change regardless of the speeds involved. 2 seconds behind at 30 mph means you are following at 88 feet and at 80 mph you are following at 235feet. Giving the distance in time makes it automatically take the speed into account.
Also, are you seriously suggesting that someone follow at over 580 feet at 80 mph? That is over 35 car lengths.
But back to fuel conservation, accelerating gently can make a huge difference in your fuel economy. When you accelerate hard, you are fighting to overcome the inertia of your car, your wheels, your crankshaft/flywheel, etc. Also, stomping on the gas in an automatic usually causes you to downshift and your engine to rev higher. At higher rpms, you also have to fight the extra friction in your engine and the extra inertia to be overcome as your pistons change direction more rapidly.
1) Go Slow
2) Go Fast (to cover more distance...?)
3) Get up a good speed, the "coast" in neutral, repeat as needed.
Number 1 won by a large stretch, which accepting the simultanious title of "Most boring"
You're thinking of hybrids. :P
This probably varies depending on your transmission type and your vehicle model, but, I ran my own MPG experiments while highway commuting in an automatic transmission sixth-gen Honda Civic (old EPA estimates: 28 city, 35 hwy) recently.
Experiment 1: I always accelerated very slowly, driving only at the speed limit, and putting the engine in Neutral at long stops. Averaged 34.88 MPG across one tank of gas.
Experiment 2: Slightly exceeded speed limits, accelerated at 80% or so on the pedal. Averaged 31.06 MPG across one tank of gas.
Experiment 3: I drove carefully as before, but this time didn't bother with putting the engine in Neutral. Still drove the speed limit and went easy on the accelerator, but just sensible slow -- not Grandma slow. 34.16 MPG this time. Shows that using neutral at stops is statistically negligible.
Experiment 4: Drove only at the speed limit, but accelerated at 80% or so. 33.2 MPG.
My conclusion was that speeding affects my mileage more than my acceleration behavior.
And yea, driving makes a differance. High RPMs are a waste of gas.
I haven't found that 100% of the time. I get about the same efficiency driving 60 as I do driving 70 (34 mpg versus 33). Driving 80 crushes my fuel efficiency though (drops it to 29 or below). You really must experiment with your car to find a comfortable medium of speed and gas efficiency.
I'm betting doing the whole coasting to a stop and so forth just won't save you much gas at all unless you can actually coast to a stop at every red light so don't put too much stock into it.
Also, do not draft cars as Stonecutter suggests, that's as brilliant as the suggestion to do some clutchless shifting in the manual transmission thread. Never try to draft, you'll end up in the ass of some angry semi driver.
In general, cars achieve good efficiency at a medium throttle, about 75% as drakmathus says. Accelerating as slowly as possible is both annoying and won't get you anything. Just be smooth, accelerate moderately, avoid lunging forward and speeding too much.
Think about it: City MPG is always going to be low and it's hard to improve it significantly if you don't go with a tiny engine (Toyota Yaris) or a hybrid engine. Highway MPG can easily be tweaked because there's very little acceleration involved in that calculation. So by tweaking the car to run efficiently at 55 MPH, you can artificially improve the mileage rating, even though in practice it'll be far lower. As a result, you want to keep your car near that speed as much as possible, to benefit from the cheating built into the system.
So if you cut out as much of the acceleration as possible by coasting where ever you can, particularly if you do a lot of highway driving, you can see pretty significant gains.
CUZ THERE'S SOMETHING IN THE MIDDLE AND IT'S GIVING ME A RASH
1) Slow is better, but make sure you're not driving slow at a high RPM. There's a lot of variations and logic to it that will make it different for every situation or car.
2) Neutraling downhill can be good, unless you shift back into drive while you're still moving. This revs the engine to a very high RPM and pretty much cancels out your desire to save gas. If you neutral downhill to a stop, then shift to drive at 0 mph, then you're okay.
Clearly I've never put numbers to perception and am completlely full of shit.
As for taking off from a light, slow is NOT always the best policy. You do not want to grandma it off the line, this is a long held belief that is actually a myth. Doing so can bog the engine for a longer period of time and actually increase gas usage. Flooring it is bad as well, for obvious reasons. You need to find a happy middleground that keeps your engine active, and in a higher RPM state for the least amount of time. It all depends on vehicle.
The difference between 50kph to 100kph stopping distance is an extra 30m on average with smaller vehicles. The stopping distance from 90kph to 120kph is almost double in most vehicles. The average person has a half second reaction time as well when it comes to braking and starting and at 80mph you cover 60 feet before you even think to put your foot on the brake. With 175 feet to stop (~54 meters) You are now going to ram the ass of the car in front of you unless your car has better brakes and you have better braking and avoidance techniques. It is 4 seconds at highway speed and 2 seconds in the city. 4 is excessive though and 2..5-3 is fine. In rain or snow, you should definitely add another second.
At the most basic level accelerating a given amount always takes the same amount of energy no matter how quickly or slowly it is done. To accelerate faster you have to apply more force but you do it for less time so it balances out. What changes is the effieciency at which the engine can generate that energy.
(Please do not gift. My game bank is already full.)
Same thing goes for highway, leave some space and watch in front of the guy in front of you to predict having to slow down. Constantly breaking/accelerating because you're too close to someone's ass is the worst thing to do (and most frustrating thing you can do when I'm a passenger).
I've been trying this out for a while and I absolutely love it when I'm driving smoothly and not revving it up to the next stop light while some jackhole is doing that and I just catch up to him every time.
Edit: This is a good article on some traffic pattern theories that will get you thinking about your effect on everyone else.
"Adaptive" cruise control systems - that use radar to measure the speed of the car in front of you and automatically change your car's speed to match - have been shown in computer simulations to reduce traffic and increase highway throughput, even if only a small minority of the cars on the freeway are using them.
the "no true scotch man" fallacy.