The domestic Hormann sectional garage door in standard form has 3 different spring and gear mechanism arrangements.
The standard Z track gear which has side springs and a headroom requirement of only 100mm is standard on door ordered up to 3048mm wide. Over that width the operating gear is the N track type which has a front mounted torsion spring and required 210mm of headroom with several descent fixing points required for the spring support brackets. The optional L track (low headroom gear) is available as an option for the N track gearing and then the torsion spring is set at the rear of the tracks and the headroom requirement is only 100mm again. The dimensions are shown below in the diagrams.