Door pulling to the left

What causes my Wayne Dalton single door to pull hard to the left?
The rollers are rubbing hard against the outtr wall of the track

Thanks

Shouldn't the door be nicely centered and balanced in between the left and the right tracks?

I have now disconnected the two counter balance cables from the bottom of my door and I also disconnected the motor arm from the door.
So, the door, a single, is now just sitting there on the rollers in the track,, all by itself,  in the open position and i can easily move it by hand but it still insists on pulling hard to the left.
It is driving me nuts
It is like ther is some, unseen force acting on it. 

A little advise please

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CHI Hardware Corporation Limited is located in China, and it is a professional manufacturer of Sectional Garage door and Industrial door hardwares and also a supplier of whole set of doors.