I am having flexibility issues going into deep back squats. If I go much past thighs parallel I begin to tilt forward or feel like I am falling backwards. I know it is a flexibility issue, but I don't know where. Please help me out so I can get a deeper squat.
Try a wider stance. Also, your back angle is supposed to change throughout the movement, towards the bottom you will need to lean forward more. Also, your knees shouldn't go much past your toes. Maybe an inch or so. Hope this helps.
Well I'm assuming it is an Olympic style squat, so his back angle should stay almost the same, and his knees should go waaay past his toes.
OP, work on the flexibility of your calves (soleus/gastroc), hams/glutes, IT band, and quads. Foam rolling would help also. Secondly, work on ankle and hip mobility. Search articles for how to do a dynamic warm-up (look for stuff by Mike Robertson, Eric Cressey, and Nick Tumminello).
Sit in the asian squat daily. Grab a pole in front of you and manuever around in the bottom of the squat to get comfortable. It takes time, but with enough effort, you will be squatting atg no problem.