Forward knees in squat

[Razor]

I am a 255lb novice lifter; 90's fat and weak , 5'10" short legs (30" inseam) long torso, big gut and flexibility of a 2x4, trying to learn correct squat form.

I have an issue squatting: I come out of the bottom postion starting on my heels but the weight seems to come forward on to my toes... After reviewing the section on squats in SS2E it appears my knees are to far forward over my toes... I have been using a TUBOW to help me with refernce on knee postion. How far forward is "just slightly ahead" of the knee?

Any help or comments are greatly appreciated

[Mark Rippetoe]

You are probably lifting your chest instead of your ass. Drive your ass all the way up without ever trying to lift your chest, and the chest will take care of itself.