By ratio... I mean how much weight can you do on a leg extension machine and divide that by how much you can do on a leg curl machine.
Quad is the front/top of your thigh. Hamstring is the back/bottom of your thigh.
Yes... if you quad is too strong and/or tight, it will literally pull on your knee cap. Here is a diagram of your knee. You can see the quad muscle connects to you knee via all those white thingies which are tendons/connective tissue (illiotibial band)... now you can imagine if you quad was too strong or too tight... it would shorten and pull on your knee (like a clingy girlfriend) causing irritation to your knee (like a clingy girlfriend).