Originally Posted by ruff
Better fuel consumtion with the smg/dct? Where do you get this? My concern is reliability. They have been "perfecting" the smg for years. Just read the M5 forum and you will get an idea how unreliable this transmission is. Anyone planning on keeping thier M3 Dct car beyond warranty better have loads of expendable cash if anything goes wrong with this electronic wizard, especially in it's first years of development. BMW has an awful track record in regards to reliability with their automatic and Smg transmissions.
No not necessarilty with SMG, I didn't say that nor do I have data to show that. However for DSG I do, DSG compared to MT mpg is available by looking at the VW GTI. EPA city/highway MPG: 23/32 manual, 25/31 DSG (in automatic mode). I suspect better results when using the DSG in manual mode and can't really explain why in highway driving DSG performs slightly worse than manual. But the tranny was in auto mode, not manual mode. "Apples to apples" should use manual mode in DSG. Perhaps also there is a gear ratio advantage to the MT.
Anyway in city driving the DSG has 9% better mpg. There is a simple scientific reason for better mileage. Except for extremely brief (single milliseconds) shift times, the transmission is putting power to the wheels ALWAYS. Add up a huge amount of throttle downs, throttle ups and the shift time of a MT when drag (air and mechanical) is slowing you down ever so slightly and you end up wasting a lot of fuel. Bottom line: DSG/DCT mpg > MT mpg.
Reliability, wizardry: M5s did have some trouble with their SMG system. However, I think it was not really that widespread. Many folks never reported any problems whatsoever. It sounds more like an overall quality, assembly, vendor problem to me. Certainly there was a problem. I won't defend BMW in the face of an obvious problem but at the same time the warranty will take care of these things. Also there was no recall done. As far as a DSG/DCT being and "electronic wizard" that really is not a fair nor accurate decription. These are both MANUAL tranmissions first and foremost. They both have a (multiple) clutch and direct gear drive systems. The electronics is simply a software program and some wiring that control actuators (mechanical!) that then in turn operate the clutch and shift lever. It is much more a mechanical system than electrical.