In the past, Bmw labeled their vehicles with straightforward designations. The initial digit represented the series and the second and third the referred to engine displacement. Sometimes an extra letter may be provided, but that would be it.
Later, however, they began using different letters such as M, Z and X for the SUVs with xDrive (AWD). So at present there are labels such as X6 xDrive 35i. But it did not end there. Bmw will now give rear-wheel-drive variants, which used to be their whole line-up, the "sDrive" name in addition to any other designation they may stick on it.
It has been seen from a long way off for the forthcoming X1, which will be available in both xDrive (All-Wheel-Drive) and sDrive (Rear-Wheel-Drive) versions. It should be noted that the present X3, X5 and X6 crossovers are exclusively all-wheel-drive copies.
It was even reported that Bmw has registered the trademarks for sDrive18, sDrive20, sDrive30 and sDrive35, as if fearing that others would try to copy the perplexing designations. If Bmw is planning a RWD for the the twin-turbo straight six in the 335i, then that's larger than the unit coming in the larger X3.
It's just anybody's guess as to what Bmw is really planning to do. There are current reports that show the sDrive plate could start emerging on other Bmw versions with rear axle propulsion, together with the substitute for the Z4 roadster that was recently caught naked.
On the front fender one can see a mark that seems a lot like "sDrive". The name is not expected to be found on the typical series versions (1, 3, 5, 6 and 7 Series), because they receive the suffix "iX" but there's no telling about that anymore.