I have 2 alto cars. In one, I am using Falken sincera 155/70 R13 and in the other one I am using Maxxis MA-P1 175/70 R12 80T OWL(outline white letters). However I did not face any problem of tires hitting the car body even on speed breakers with both sizes. 175/70 in my experience gives better grip, better looks and smooth ride. As far as CNG consumption and engine racing is concerned, you will hardly feel any change. I also recommend MAXXIS MA-P1. I have found that the life of these tires is really very long. I have been using them since 3 years but they still look new and even wear and tear is negligible. FALKEN sincera were comparatively not better than MAXXIS.