I like doing deep squats. I wish to focus on legs only. But when im doing my working set, at the bottom position, to get the weight up my back tilts forward and so im using more of my back than my legs. I wish to go strait up and down, using my legs Only. But i start tilting forward in the bottom postions.
Anyone know how I can correct this?
You could always try going with a lighter weight that allows you to use proper form. 
Other suggestions would include getting the bar lower on your back, picking a point high on the wall to focus on during the rep to keep your head (and back) up. But mainly it’s a weight thing.
Of course you could also try front squats. But so what if you work your back a little? That’s just part of the game. Squats are considered a full body exercise, not an isolation exercise for the legs.
Have you tried typing “Squat” into the search engine? There are lots of good articles here.
Elevate your heels by using a block, or buy a pair of olympic lifting shoes.
I find it helps to focus on my heels when doing squats. If you can feel the weight coming down on your heels, your form is right. Oddly enough, I also find that if I watch myself in the mirrors when doing squats I tend to use my back too much. When I just concentrate on the weight and its position and pressure on my heels and not look at myself I do my squats with good form. Also, your legs may be too close together. I find that to do a proper deep squat I need to have my feet planted slightly wider than my shoulders and my toes planted a little out. But then, I have pretty average shoulder width. If you are broad shouldered that may be too wide. This is not textbook lifting I am giving you, this is just what seems to work for me.
Watch the arches of your feet if you use a block. They are unsupported and carrying a lot of weight. At our humble gym we have a sloping block for this reason, actually I never asked why but I assume so.
You just need to work a little on you flexibility. Try using a 1x4 for a while. You can eventually wean yourself off of it. Put for the effort and you’ll get there!
Is is just as you fatigue that your torso pitches forward? If so, strengthening your lower back via deads and good mornings will help tremendously; if not, then you should just go lighter and fix your form.
How far apart do you grip the bar? One technique that can be used to stay more upright is to grasp the bar as close as possible when you are setting up. From that point, make sure that during your set your elbows are pointing straight down. This will help you stay more upright.
If your hands are spaced far apart, your elbows will automatically point backward and you will end up bending forward at the bottom of the squat to counterbalance this.
As far as elevating your heels, while this may keep you more upright, Ken Kinakin says it inhibits the firing of the posterior chain.
WUT?
I beg the differ gentlemen.
not lower on your back I say higher!
focusing on the heels is for deads and back squats. here u wont need it.
logic:
If u want to squat staright up and down as an olympic lifter does, the higher the bar goes, the more every inch of forward bend counts in moving your centre of gravity and thus allowing a lesser forward bend.
When I changed the position of the bar to my shoulders, I added instant pounds also and was able to squat deeper easily!
The trick is (although it demands forearm and shoulder flexibilty - if u ever heard it mentioned with squat and couldny imagine why now you will know)
go under the bar, place your palms pretty wide, and raise your elbows till yourms are paralel to the floor. this will make the bar “sit” on your shoulders. this is gonna hurt at the begining, especialy since u can suddenly use more weight… suck it sissy! or u could be smart and put a towel. dont let the elbows drop during the rep.
U will probably find that your stance will vary a little bit (u may have to flare your knees more) but u can go deeper easily, and keep that lumbar arch all the way!
hope this helps.
S-man
there isn’t an easy answer to your problem. If you are training for the movement, then Thunder is right. A wide stance shortens the knee -to-hip distance and w/ a close grip elbows pull forward will give you max. strength. But if you are training for the quads., then a closer stance, or elevated heels( if you lack a lot of flexiblity in your ankles), or even smith mach. squats will put the focus in the quad.
A lot of times when you use a wider grip your back is not tight enough under heavier lbs. so in order to feel the tight back you end up leaning over til it tenses to support the weight. but if you have a close grip from the set-up, your back will be pull tight and you will remain more in the upright pos. My max moved up 90lbs in about two wks w/ this small adjustment
hope that helps, Guru X
My grip is not wide, I bring my neck and head back as im doing them.
My stance is a little wider than shoulder width, with toes pointing out a bit.
Mainly, im focusing on Lep Power/strength. Which means I need the glutes and hams involved. Ofcoarse I want huge quads also.
Thunder and everyone else, Im gonna try what you all suggested and see if it works for me.