I have seen the explanation on "How bicycle gear works?" but this seem to be using a standard round chain ring. I would like to know if there is any difference when an oval chain ring is used. As I can clearly see, one can have an oval chain ring on a fixed/single gear bike. There fore there is no slaking or tightening of the chain. So I would say that there is no difference in gear ratio during the complete rotation of the oval-chain-ring. So the torque will remain the same. 

Is there an answer to my problem? and if there is could you proved any equations