[tame3902]

> I have to admit though that the automatic is way faster than me at changing gears, which helps keeping a constant acceleration and avoid head bobbing.

That's because a DSG gearbox has two clutches. It is basically a traditional gearbox with one clutch connected to the odd gears and one to the even gears. The system selects the next gear according to the revs of the engine and does all the physical shifting in advance. The actual gear change is then only disengaging one clutch while engaging the other one. You can overlap this so the engine continously delivers torque to the wheels. Thus, no head bobbing.

[serf]

>You can overlap this so the engine continously delivers torque to the wheels. Thus, no head bobbing.

head bobbing (sudden g-force jerks) was fixed before the introduction of another clutch; that's a function of rev-matching between upshifts and downshifts. An early BMW SMG system, a manual gearbox with electro-hydraulics on top of it to handle shifting and clutch work, gets rid of the head bobbing.

How? Precise rev-matching.

dual clutch systems were a means to speed the gear-shift process up, with two clutches there is no need to wait for shaft speed mismatches, you just keep the opposite clutch where you need it RPM-wise. This helps alleviate the head-bobbing, but it's more just an artifact of how the system has to work -- rev-matching is now something required in order not to blow the system up.

tl;dr : it's the rev-matching saving your neck, just like it would've been doing had you been a passenger with a race driver -- but they're doing it to save tires and keep the car stable, they probably don't care about your neck.