My understanding is that reclining too far puts the strain of supporting your torso on muscles (which have to do work) rather than bone/cartilage (which is better suited to static loads). This, of course, is problematic for folks with disc problems, but I think the closer you sit to upright, the less strain you'll feel. And that applies both to seatback angle, and sitting straight up rather than draped over the console.
FWIW, when I went to the PDC for the M5 Driving Experience (2003 or so), they spent about half an hour showing us how to properly adjust the seat. Here's the points I remember:
* Head two to four fingers from the roof. You get a better overall view, and can see more of the road close to the car.
* Left leg on the dead pedal with a slight bend in the knee. If you can straighten your leg, you risk severe leg injury in a collision. You should still be able to press the clutch pedal all the way in.
* Hands at 9 and 3, elbows bent. You have more leverage and can turn the wheel further from that position. It puts much less strain on your neck and shoulders than 10 and 2 or -- heaven forbid -- draping one wrist over the top of the wheel.
'11 F10 550i M Sport (ED Aug 1, 2011; US deliv, Sep 12, 2011)
'08 E90 M3
'07 E92 335i
: ordered Nov '06; delivered Jan '07, totaled Sep '08.
'02 E39 M5
: June 2002 - June 2007
'00 E39 540i/6
, '97 E39 528i
, '92 E34 525i
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