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niky · 12-31-2012, 11:06 PM

The advantage of dual clutch is the removal of torque converter losses. But it's clunky to use, and DCTs are heavy buggers. On-paper, they can match or exceed manuals, though.

But that's on-paper. In my experience, over several cars, including the Focus diesel, the Fiesta and the new Focus GDI, dual-clutches can match a well-driven manual on the highway, but in-traffic driving sees them suffer from the extra drivetrain weight. And the non-serviceable "lifetime" units are a nightmare. It's telling that Ford started offering replacement clutch packs for the Fiesta. They cost twice as much as traditional clutches (heck, there are two of them, so it makes sense), but at least you have the option.

CVTs are either as good or better than manuals or almost as good, depending on the implementation. By far the MOST economical automatic non-hybrid I've ever driven has been the Honda Fit 1.3 iDSi with the CVT. Ultra-light, ultra-low friction drivetrain, fantastic motor and car. 70 mpg easy. The only cars I've driven can do better are sub-liter cars.

BUT: Honda's CVT has a reputation for fragility, especially since they designed the stupid clutch packs to be non-serviceable items. Mitsubishi and Nissan get around this by using stronger steel belts and torque converters for smoothness. Adding a torque converter takes away from the efficiency bonuses, but if it has electronic locking (so it can lock up just off idle in high gears), it's not such a big issue. Mitsubishi's Mirage CVT with the 1.2 supposedly does almost 50 mpg on the highway.

New "traditional" automatics still have a lot of life left in them. Super-low-friction fluids, locking torque converters and lots and lots of ratios make for pretty good economy. They're not as fiddly as DCTs or as "unnatural" as CVTs, but once you have seven or eight speeds, the ratios are so close together that they start feeling like CVTs. Call it the "uncanny valley" of transmission ratios, but I can't imagine any criticism against CVTs that doesn't apply to these new eight-speed plus boxes. I drove a new Genesis Coupe for a week, and the eight speed box felt less "exciting" than the old six. That "kick" when you dropped two thousand rpm between gears was completely gone, replaced by nearly seamless acceleration.

Personally, I think CVTs, despite the "unnatural" feel, are the way to go. You avoid the jerky feel of DCTs in traffic, and adding a torque converter preserves clutch pack life. If you go for a dry clutch pack, you can still make it smoother than a DCT, and with clever programming, you can keep the dry system economy benefits while giving it longer clutch pack life. And if you really need the "feel" of gearchanges for one reason or another, a simulated five/six/seven speed mode will give you that, with less lag than in a traditional auto.

12-31-2012, 11:06 PM	#9 (permalink)
niky Master EcoModder Join Date: Aug 2010 Location: Philippines Posts: 2,173 Thanks: 1,739 Thanked 589 Times in 401 Posts	The advantage of dual clutch is the removal of torque converter losses. But it's clunky to use, and DCTs are heavy buggers. On-paper, they can match or exceed manuals, though. But that's on-paper. In my experience, over several cars, including the Focus diesel, the Fiesta and the new Focus GDI, dual-clutches can match a well-driven manual on the highway, but in-traffic driving sees them suffer from the extra drivetrain weight. And the non-serviceable "lifetime" units are a nightmare. It's telling that Ford started offering replacement clutch packs for the Fiesta. They cost twice as much as traditional clutches (heck, there are two of them, so it makes sense), but at least you have the option. CVTs are either as good or better than manuals or almost as good, depending on the implementation. By far the MOST economical automatic non-hybrid I've ever driven has been the Honda Fit 1.3 iDSi with the CVT. Ultra-light, ultra-low friction drivetrain, fantastic motor and car. 70 mpg easy. The only cars I've driven can do better are sub-liter cars. BUT: Honda's CVT has a reputation for fragility, especially since they designed the stupid clutch packs to be non-serviceable items. Mitsubishi and Nissan get around this by using stronger steel belts and torque converters for smoothness. Adding a torque converter takes away from the efficiency bonuses, but if it has electronic locking (so it can lock up just off idle in high gears), it's not such a big issue. Mitsubishi's Mirage CVT with the 1.2 supposedly does almost 50 mpg on the highway. New "traditional" automatics still have a lot of life left in them. Super-low-friction fluids, locking torque converters and lots and lots of ratios make for pretty good economy. They're not as fiddly as DCTs or as "unnatural" as CVTs, but once you have seven or eight speeds, the ratios are so close together that they start feeling like CVTs. Call it the "uncanny valley" of transmission ratios, but I can't imagine any criticism against CVTs that doesn't apply to these new eight-speed plus boxes. I drove a new Genesis Coupe for a week, and the eight speed box felt less "exciting" than the old six. That "kick" when you dropped two thousand rpm between gears was completely gone, replaced by nearly seamless acceleration. Personally, I think CVTs, despite the "unnatural" feel, are the way to go. You avoid the jerky feel of DCTs in traffic, and adding a torque converter preserves clutch pack life. If you go for a dry clutch pack, you can still make it smoother than a DCT, and with clever programming, you can keep the dry system economy benefits while giving it longer clutch pack life. And if you really need the "feel" of gearchanges for one reason or another, a simulated five/six/seven speed mode will give you that, with less lag than in a traditional auto.