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Fanch said:
Actually, I did use for a while one of those support belt around my lower back, didn't help much to be honest.
Francois, that shouldn't help much I'm afraid. The most important part in long drives is the proper alignment of the lumbar spine when seated in the car. The elemental part is to maintain the lumbar vertebrae in their natural lordosis while seated, which is the foward saggital curve your lower back has. This curve is very important for the proper distribution of loads between the posterior joints and intervertebral disc of the lumbar vertebrae, also decreases intradiscal pressure and allows for the maximun axial loading capacity and shock dissipation of the lumbars.
Becuase the seats in the cars are placed low on the floor unlike a normal chair which is higher, and becuase your legs are elevated with respect to the seat to control the pedals, you tend to sit more laid backwards and combined with the pull from the hamstring muscles tends to place the pelvis into flexion which in turn flexes the lumbars (removes the lordosis). This hypolordotic posture added to the fact that the car vibrates and bounces on the road irregularities transmits those forces to the spine and causes microtrauma of the joints and fatigue of the stabilising muscles and associated conective tissues leading to injury. A more correct sitting posture greatly reduces this since the spinal joints are in a more mechanically efficient relation to deal with this.
First adjust lumbar support to the maximum setting (the more it sticks out the better in orther to "push" the curve into the spine and not allow the lower back to flex). If the seat does not have an adjustable lumbar support you can buy a lumbar pillow designed for car seats which work very well (very often better than the lumbar support incorporated into the seats).
Then raise the seat as high as posible and tilt the seat bottom foward (in a descending plane fowards) in order to decrease the flexion of the thighs at the hip and reduce the hamstring tension (this is why SUV, vans and truck are more confortable for lowback problems since you sit "higher" than on cars).
Then bring the backrest to a vertical position or close to it, it doesn't have to be 90* but as upright as you confortably can.
And lastly, the greater lateral suppport the seats have the better since the trunk is more stabilised in the curves and lateral G's therefore reducing the work and fatigue the paraspinal musculature has to do to stabilise the trunk, so the adaptive seats car makers are coming out now (like the M3 or 997) are recommended for this since you can adjust the lateral support for your particular upperbody frame.
Hope this helps
. Did you already take it to the track?
Get a pillow!!! 
).
