https://f80.bimmerpost.com/forums/sh...&highlight=DCT
Quote:
Originally Posted by CanAutM3
I am hugely disappointed with the DCT specs on the F8X so far 
That 89lb penalty is the first blow.
I also find that the gear ratios have been poorly selected for optimal acceleration performance. The DCT essentially has similar total ratio spacing as the 6MT between 1st and 6th, I even find that the ratios on the DCT are worse than on the 6MT . The lower gears have too much spacing while the higher gears are too tightly spaced to properly leverage the S55 power curve. 1st gear is so highly de-multiplied, that it will be impossible to put the power down. I think it was selected mostly to make the engine feel responsive in off boost puttering around. 7th is only an additional overdrive beyond 6th for fuel economy; having 7 gears is no longer used as an advantage for acceleration (tighter overall gear ratio spacing).
Looking at BMW published acceleration numbers ( http://www.bmw.de/dam/brandBM/market...2975025706.pdf), the DCT has a 0.2s advantage over the 6MT from 0-100km/h. However, that 0.2s gap is maintained from 0-200km/h. I would have thought that the DCT quick shifts (2 more shifts needed to go from 100-200km/h) would have widened the gap. It seems that the lighter weight and/or better efficiency of the 6MT allow it too keep up with the DCT in that speed range.
Further, looking at the 80-120km/h pick-up numbers in 5th gear, the DCT is slower by 0.1s. Both cars have the same 5th gear overall ratio. Further, the 6MT matches the DCT 4th gear 80-120km/h despite the DCT having a slight gear ratio advantage in 4th. So I can only assume that the additional weight and losses of the DCT are the culprit.
We will have to wait for independent tests to confirm any of this. In the meantime, going with the numbers available to us, my feeling is that BMW went cheap on us for the DCT on the F8X  . |
^ good read on the gear ratios between the two cars. Basically the DCT and 6 speed share the first six gear ratios... and the DCT 7th is just there for fuel economy. You would think they would equally space all the gears to give the dct an even further acceleration advantage.