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| tom66:
An automatic dual-clutch transmission is just as efficient as a manual transmission. Arguably it is even more efficient because it can swap gears more quickly due to the built-in rev-matching, which leads to less time when the clutch is slipping or when no power is applied (fuel burn but with no output.) That's especially important for city driving, but when on the highway roughly all automatic and manual transmissions behave similarly, due to most modern automatic transmissions having a lockout for the torque converter. |
| tooki:
--- Quote from: JPortici on April 03, 2022, 12:58:09 pm --- --- Quote from: Halcyon on April 03, 2022, 07:28:57 am ---You can add automatic versus manual transmission to that list these days. I know there are purists out there who will argue that manual transmissions give them "greater control" over the vehicle, which is just bollocks in my eyes, but the fact remains, a well designed modern automatic transmission is better than old manual boxes in every way, including fuel economy. --- End quote --- I have yet to see one automatic transmission that doesn't add at least 0.5l/100km --- End quote --- Then you haven’t looked at cars in a very long time, and/or haven’t looked carefully enough. It’s honestly kind of hard to compare with most cars, because they often don’t let you choose the transmission without also changing a bunch of other stuff at the same time, whose weight differences invalidate the transmission comparison. But for example, in the BMW 1 series, where you actually can choose multiple engines and transmissions independently, only on the 116d does the manual transmission potentially save fuel. And I say potentially, because only one end of the consumption range changed, and only by 0.1L/100km. On every other engine type, choosing automatic either has no effect whatsoever, or reduces fuel consumption. This is how it’s been for many years now. The reason manual transmissions used to be so much more efficient in the past is because they had more gears than automatics. (E.g. in the 80s, a compact car might have a 5-speed manual, but only a 3-speed automatic.) But we now generally have the same number of gears in an automatic (6 being really common now), and a smart computer deciding when to switch. That computer will, on average, do better at switching gears than an average driver. |
| tooki:
--- Quote from: Monkeh on April 03, 2022, 02:31:39 pm ---DCTs are quite capable of being more efficient than manuals in the hands of the average driver - none of the usual auto losses, and you take the incompetent person out of the loop (and replace them with engineers who don't drive real roads, but that's another argument). --- End quote --- What a silly statement. Of course they drive on real roads. But if they programmed the transmission ECU to behave the way they’d like, the car would never meet its emissions and fuel efficiency targets. And that’s why we have the switch to choose between eco, standard, and sport modes: the first one for advertisements, the second as a happy compromise, and the third “this is how we’d like it to behave if fuel consumption were no object”. |
| Monkeh:
--- Quote from: tooki on April 03, 2022, 07:25:24 pm --- --- Quote from: Monkeh on April 03, 2022, 02:31:39 pm ---DCTs are quite capable of being more efficient than manuals in the hands of the average driver - none of the usual auto losses, and you take the incompetent person out of the loop (and replace them with engineers who don't drive real roads, but that's another argument). --- End quote --- What a silly statement. Of course they drive on real roads. But if they programmed the transmission ECU to behave the way they’d like, the car would never meet its emissions and fuel efficiency targets. And that’s why we have the switch to choose between eco, standard, and sport modes: the first one for advertisements, the second as a happy compromise, and the third “this is how we’d like it to behave if fuel consumption were no object”. --- End quote --- I was not suggesting they don't feel good - rather that they make inferior choices for fuel efficiency when confronted with real world hills, not idealised test tracks and driving around Heathrow airport. However, they're still far better than the average driver. |
| tom66:
--- Quote from: tooki on April 03, 2022, 07:21:02 pm ---The reason manual transmissions used to be so much more efficient in the past is because they had more gears than automatics. (E.g. in the 80s, a compact car might have a 5-speed manual, but only a 3-speed automatic.) But we now generally have the same number of gears in an automatic (6 being really common now), and a smart computer deciding when to switch. That computer will, on average, do better at switching gears than an average driver. --- End quote --- This is really important. On my Golf, doing 70 mph (~120 km/h) up a modestly steep hill the transmission shifts from 6th to 5th. You can happily manually switch it back to 6th and the car runs fine, but the fuel consumption is noticeably higher (~5-10%). Most drivers would say in 6th because the "highest possible gear is usually the best for fuel economy" in car mythology, but of course the ECU has a precise mapping of fuel burn vs torque vs engine speed, and it knows it can still provide the required torque in that gear whilst lowering fuel burn, despite increasing engine RPM. |
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