Have you changed the fuel station in the last time refill? Your engine is knocking and you are getting bad mileage. There is a good chance that you have bad quality fuel in your tank.
These tires cannot put the difference of more then 0.1 Km/L which will mean maximum 20-30 Kms difference overall.
Sir wasay I am against this rotalla thing but main bola es lyaie nahi kah ab dalwa lyaie hain to kia ho sakta hay. The china stuff gets more wear and tear and there is a good change that it will become difficult to balance such stuff.
Are you sure balancing was properly done when you put them in?
Sir there is another thing. You would be utilizing A/C far more from your last fill. Kia khyal hay? That will too affect the mileage.
Anyways. Lets see when your tank gets empty to kia hota hay. At least two or three tanks kay baad hi proper mileage ka pata lagta hay.
In summary, Keep three things in mind:
1) The Fuel quality.
2) A/C usage.