351–360 of 893 posts
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I was referring to the misinformation about higher fuel efficiency of manual compared to automatic. I heard it too in driving school.
The real question is: Will it save more money in gas than it costs extra to buy?
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>when automatic transmissions are consistently outperforming humans at fuel efficiency Do you have data to back this up? Unless you're driving a dual clutch "dry" transmission or a CVT, because of Physics, an automatic transmission will always be less efficient. The Automatic transmission Torque converter [1] will waste some of the energy provided by the engine, especially with city driving. Also, most automatic cars…
> It's well known that accelerating rather quickly to your cruise speed is the optimal strategy for fuel efficiency, hence the reason to switch from 3rd to 5th gear directly. I don't mean to be pedantic, but I think your logic is backwards here, ie. It's well known that 5th (top) gear is the most fuel efficient, hence the reason to accelerate to it rather quickly (the optimal rate would vary between cars), I think wo…
It's a waste of energy and clutch/gearbox actuation to use the in between gears and there's never anything wrong with being in a low gear at any point unless your engine hits the red line.
On most cars fourth gear is really for cruising at a lower speed than is comfortable (or safe) in fifth.
You can also very easily downshift sequentially through the gearbox. Downshifting through several gears takes much more practice to do properly and isn't very useful on the road.
I got my driver's license in Sweden, and the official driving handbook completely worships manual transmissions, and makes several untrue claims about how much better they are than automatics. You can choose to do your road test in an automatic, but that'll earn you a restriction on your license, barring you from driving a manual. It's probably fair, but almost everyone (myself included) chooses to practice in manual…
>when automatic transmissions are consistently outperforming humans at fuel efficiency Do you have data to back this up? Unless you're driving a dual clutch "dry" transmission or a CVT, because of Physics, an automatic transmission will always be less efficient. The Automatic transmission Torque converter [1] will waste some of the energy provided by the engine, especially with city driving. Also, most automatic cars…
In the UK you will fail your driving test if you coast, and in some countries / states it is illegal - with good reason.
Just google it - not a single article supporting your argument.
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wow, you are incorrect in almost every statement. I get it, you like easy driving without worrying about clutch and gears, but not everybody is like that. I would never want automatic transmission for my car, it's inferior, expensive, less fun and car has no way knowing details of road situation I am facing and choices I am about to make. And I am far from petrolhead person FYI. Another point - I don't know a single…
> it's inferior, expensive, less > fun and car has no way knowing > details of road situation I agree, and have believed those things since my mother (literally) taught me them! But I've never driven an automatic, and the small number of people I know in the UK who have switched to an automatic are never, ever going back. Food for thought.
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I've driven manuals most of my life. Before stop/start came along, I was in the habit of just holding the clutch pedal down while stopped at intersections or in traffic. Anecdotally, I think most drivers do the same. Now, when driving stop/start equipped vehicles, I always try to use it. But in a manual, it does takes more thinking and effort and I wonder how many casual drivers actually bother. The thing is, most of…
> I was in the habit of just holding the clutch pedal down while stopped at intersections or in traffic. If you take a driving test in the UK and do this, that would be a minor fault. You can only have a few minor faults before you fail the test. The rationale is that you need to be in full control of the car at all times, and when you set off you mustn't drift backwards at all . The easiest way to do this without ne…
And now days, newwer cars have the "hill hold" feature which automatically prevents you rolling backwards anyway.
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>when automatic transmissions are consistently outperforming humans at fuel efficiency Do you have data to back this up? Unless you're driving a dual clutch "dry" transmission or a CVT, because of Physics, an automatic transmission will always be less efficient. The Automatic transmission Torque converter [1] will waste some of the energy provided by the engine, especially with city driving. Also, most automatic cars…
In modern cars, disengaging the clutch (or using neutral) when coasting (toward a stop or down a hill) is less efficient than staying in gear. This is because it takes some fuel to keep the engine idling, where staying in gear allows the computer to completely cut fuel flow, as long as the forward motion is keeping the engine turning.
(Left-foot braking is a technique where you keep the power down in a bend but dab the brake to adjust the fore-aft balance of the car. It is common in rallying - there is some awesome footage somewhere on YouTube of the driver's feet in an 80s rally car. His feet move so fast it looks like he is dancing on the pedals.)
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Eco driving is also about driving with foresight: don't accelerate if you likely have to stop soon anyway. Braking wastes the most gas.
Yah, this can make an overwhelming difference in the long run. I used to drive semi-regularly between Wisconsin and Minnesota, a stretch of about 280 miles; others in my family would make the same trip with the same car during the same times of year, and my mileage per tank was always significantly different, and we couldn't figure out why initially. Turns out they used cruise control for most of the stretch, which I…
I'm in US, and am always struggling to find new cars when I'm ready to buy because of this probably. Just recently I visited a dealership where the sales guy told me flat out "manual transmissions are extremely rare anymore". It may be a diagnose-able issue :) but I was a wreck (literally) when I first started driving because I would lose focus on the road. Manual transmission, it seems to me, gives me a far better "…
In India, it's the opposite. Very few vehicles have automatic transmission, major reason being mileage.
An equivalent automatic transmission adds one or two thousand dollars to the car, which is unaffordable to most (for no perceived gain).
We buy lots of Indian-made cars here (mostly Marutis but some Tatas too), the other cheap cars being Chinese.
I got my driver's license in Sweden, and the official driving handbook completely worships manual transmissions, and makes several untrue claims about how much better they are than automatics. You can choose to do your road test in an automatic, but that'll earn you a restriction on your license, barring you from driving a manual. It's probably fair, but almost everyone (myself included) chooses to practice in manual…
>when automatic transmissions are consistently outperforming humans at fuel efficiency Do you have data to back this up? Unless you're driving a dual clutch "dry" transmission or a CVT, because of Physics, an automatic transmission will always be less efficient. The Automatic transmission Torque converter [1] will waste some of the energy provided by the engine, especially with city driving. Also, most automatic cars…
* Mazda 6 2.5L SkyActiv-G MT: 25/37 MPG
* Mazda 6 2.5L SkyActiv-G AT: 26/38 MPG (28/40 MPG in Grand Touring model, not available in MT)
As for the torque converter inefficiency - that is true only for some ancient transmissions. A modern torque converter will waste some energy only during shifting the gears. After synchronization, the torque converter is locked and the connection between the engine and the wheels is mechanical, just as in MT.
"It's well known that accelerating rather quickly to your cruise speed is the optimal strategy for fuel efficiency"
And now - any data to back this up? I don't have hard data, but I have some hard theory. Modern engines have variable valve timing technology which allow them to work in a much more efficient thermodynamic cycle when under light load and low RPMs. When you're not using the full torque of the engine it works in something like an Atkinson or Miller cycle, with high compression ratio and much higher thermodynamic efficiency. A bad thing about Atkinson-like operation (achieved by keeping the inlet valve open longer than normally) is that it reduces the effective capacity and hence power of the engine. So if you press the accelerator pedal fully, the ECU switches the engine to a classical Otto cycle, which is less fuel efficient but gives more power. Hence, if you accelerate fast, your mileage will be worse, not better.
Another issue is that keeping high RPM at low gear (possible with turbocharger running on full pressure) to accelerate fast makes it harder to control burning all the fuel efficiently because there is less time to do that in each cycle. And also the temperature of the cylinders goes quickly up which makes it harder to avoid detonation. So in order to not destroy the engine, the ECU will adapt the injection / spark / valve timings and lambda coefficient to avoid explosive burning of the fuel by decreasing the effective compression-ratio and increasing lambda to decrease the temperature. Lower compression-ratio and higher lambda means lower fuel efficiency.
That's why when I "eco drive", the ECU keeps the gear extremely high, so that the engine works typically in a range 1000-1500 RPM. Now this is quite hard to achieve in practice when driving an MT car, because whenever you want to accelerate faster, you'd have to gear-down by 2 or 3. That's why ATs are better for fuel efficiency.
BTW: I do own 2 cars, one with MT, one with classical hydrokinetic AT, so I have a comparison. I'd really not be able to drive my MT car using such high gears as my AT car can. And also I can't switch gears so fast as an AT can do, even though my AT is not the fastest among all ATs.