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The (Don't Yawn!) Fuel Economy thread!
- Thread starter dazzer21
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Coast around a corner?
You definitely drive around corners.
But that's not what I said, is it?
As you approach the turn the transmission is going to be slipped into neutral at some point, possibly 100 or 200 feet before the turn depending on the situation, then downshifted to make the turn. Whenever the clutch is depressed, you are coasting -- which some contend is an inherently dangerous situation. My point is that manual transmission drivers are in neutral all the time. It's a required state for the shifting of gears.
My Fuel economy history (all cars manual transmission and over 100k miles while I owned them):
1986 Toyota Pickup. 25mpg combined cycle with very aggressive teenage driving.
1994 Toyota Pickup. About 25mpg combined cycle. See above.
1999 Nissan Altima GXE. Usually averaged around 31.5-32mpg combined. Farthest I ever went on a tank (15.9gal) was 498 miles, averaging around 31mpg. Best observed economy was 39.5mpg on a 360 mile trip where I kept it at or under 60mph the whole way. A torquey engine with a fat power band means less shifting. Surprisingly efficient for a 2900 pound car with a 2.4 liter engine.
2000 Subaru Forester S. Current car, averages about 27.5 mpg highway @ 70-75mph. If I keep it below 65 I can hit about 31-32mpg. About 25-26mpg city. The gear ratios on this (fairly heavy) car are too short for optimum fuel economy. It needs either a taller fifth gear or a sixth gear for highway driving.
I drive fairly aggressively, don't coast in neutral and often perform heel-toe down shifts or double-clutch, so a hypermiler would probably see significantly better fuel economy.
1986 Toyota Pickup. 25mpg combined cycle with very aggressive teenage driving.
1994 Toyota Pickup. About 25mpg combined cycle. See above.
1999 Nissan Altima GXE. Usually averaged around 31.5-32mpg combined. Farthest I ever went on a tank (15.9gal) was 498 miles, averaging around 31mpg. Best observed economy was 39.5mpg on a 360 mile trip where I kept it at or under 60mph the whole way. A torquey engine with a fat power band means less shifting. Surprisingly efficient for a 2900 pound car with a 2.4 liter engine.
2000 Subaru Forester S. Current car, averages about 27.5 mpg highway @ 70-75mph. If I keep it below 65 I can hit about 31-32mpg. About 25-26mpg city. The gear ratios on this (fairly heavy) car are too short for optimum fuel economy. It needs either a taller fifth gear or a sixth gear for highway driving.
I drive fairly aggressively, don't coast in neutral and often perform heel-toe down shifts or double-clutch, so a hypermiler would probably see significantly better fuel economy.
Bah, pure pedantryChanging gears only takes about half a second, which is hardly enough to constitute fully-blown 'coasting'.
Yeah, but I understand where IJ Reilly is coming from. My Acura is stick, and I coast quite a bit as a result. If I'm coming off a freeway offramp and slowing to the light ahead, I'll slow while in gear, maybe downshift once or twice (and wearing my clutch as a result as he said), but I'm not going to downshift through all five gears before I get to the light. Obviously I can't get too slow while in gear in 3rd or 4th, so there'll be a point where I coast the rest of the way to the stop. If I need to suddenly go - I just drop the clutch and off I go.
I hear ya. I have the same Jeep and I love it. I'm getting around 20-22 MPG. I drive on the highway most of the time. It's too bad they don't make the Cherokee anymore. It was the best best Jeep they ever made.
Bah, pure pedantry
Do you drive a manual? I don't know why anyone would stay shifted in a high gear while they slow down and a lower gear will be needed. I often coast 200-300 feet before downshifting in cornering situations and more when exiting freeways or approaching a red light. You press the clutch pedal, put the stick in a neutral position, and get ready to select the next gear you'll need.
If I'm exiting a freeway, I usually coast in top gear until I'm going about 30mph, braking as necessary until the engine is near idle speed. Then I shift into neutral and come to a stop.
Going around corners I usually leave the car in 4th, unless the corner is tight enough that I need to down shift. I rarely use 3rd when driving in towns - I shift 1-2-4. Before I bought my AWD car I would start in second and shift into 4th in winter.
When driving aggressively I use all the gears, revving high and double-clutching on the way up and heel-toe down shifting. Fun, though not economical.
I live on a hill, so technically I can roll the first 500 feet to wherever I'm going without turning the car on...though I lose all the power assist on the steering and brakes!
Why is coasting in neutral dangerous?
I want to be open-minded about this idea, but I just can't picture a likely scenario in which coasting in neutral increases my accident risk. In 23 years of driving, I can't recall a single panic situation that required me to accelerate quickly. Look out, hit the gas!
Can anyone describe a situation that isn't too far-fetched?
(And just to answer the OP, I get about 40MPG mixed local/highway in my '92 Civic with manual transmission. A little better in the summer, a bit less in winter.)
I want to be open-minded about this idea, but I just can't picture a likely scenario in which coasting in neutral increases my accident risk. In 23 years of driving, I can't recall a single panic situation that required me to accelerate quickly. Look out, hit the gas!
Can anyone describe a situation that isn't too far-fetched?
(And just to answer the OP, I get about 40MPG mixed local/highway in my '92 Civic with manual transmission. A little better in the summer, a bit less in winter.)
I don't think it's dangerous. If you adopt a driving style that calls for more shifting activity it's obviously going to put more wear on the clutch, but other than that I can't see a downside...
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fair enough I guess. It's still illegal in some jurisdictions and it wastes more has and potentially puts more wear on the clutch, so why do it?
apearlman said:
fair enough I guess. It's still illegal in some jurisdictions and it wastes more has and potentially puts more wear on the clutch, so why do it?
If you are right that coasting in neutral is "illegal in some jurisdictions", I can't think of a more unenforceable law...how on earth can police tell whether or not you are in gear?
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I agree with you on that. I have no idea how you would enforce such a law. But apparentley, it's on the books in some cities.
Lord Blackadder said:
I agree with you on that. I have no idea how you would enforce such a law. But apparentley, it's on the books in some cities.
Downshifting and coasting in gear are two different things. Furthermore, we are not talking about coasting for the purpose of braking, we are talking about going down a hill and coasting in gear vs. out of gear. If you leave it in the same gear you were in at the top of the hill and go down the hill, you are not adding wear to your clutch.
Yes, shifting adds wear to your clutch. No, leaving it in gear not not add wear.
It's no extra effort at all really, just a matter of timing the shift differently so you get the benefit of momentum and downshifting into the turn. It's the way I learned, and I suppose since I've been driving this way for over 35 years, it's hard to imagine another way.
Shall we move on, and speak to trip economy (1), or even 'economy of scale' economy (2)??
(1) Plan for more than one stop when taking the car out.
(2) Invite a friend along. They need not drive too, if they have close to the same needs as you do.
Number 2 is the hardest sell of all. We have become accustomed to "doing our own thing, on our own time."
This type of thinking has to be modified.
(1) Plan for more than one stop when taking the car out.
(2) Invite a friend along. They need not drive too, if they have close to the same needs as you do.
Number 2 is the hardest sell of all. We have become accustomed to "doing our own thing, on our own time."
This type of thinking has to be modified.
"We" are talking about a number of things, and I never suggested that leaving the transmission in gear adds wear to the clutch. What I did say is that downshifting for the purpose of engine braking does.
I was more point out that part that you said it was better for manual to stay in neutrel because of engine breaking. Most of the time when we are slowing to a stop or coasting chances are we are starting at 45+ mph so we should be in a one of our top gears this going about the neutral part.
As for the turns yeah I know what you mean about the clutch being in and what not. I would not call it neutral though. I call neutral only when the car is truly in neutral which more off than not when I am slowing to a stop when I hit the clutch I am in neutral.
For all practical purposes, whenever the clutch is engaged or you are between gears, you're in neutral. As for it being better to be in neutral, I am assuming (for lack of any evidence to the contrary) that adding engine braking slows the car more quickly, so if the objective is to make the most out of momentum, then taking the car out of gear would be the most effective way. Apparently some are arguing that cars use more fuel coasting at idle than they do coasting in gear. I don't see how that can be true (it seems counterintuitive), but I'm open to persuasion if some hard evidence is presented.
With the exception of traffic being really backed up or a really short off-ramp, why are you slowing down before the ramp?
