Nano is safe - mileage depens on user
Nano on a practical note gives only 18-19 kmpl in City with AC. On highways it gives 22-24 kmpl or more, but I'm skeptical about its safety in highways.
Hi Anshuman, Nano is safer than a few other entry level hatches (atleast on a frontal collision). There are pretty strong beams in rear and underbody. Nano is less of a monocoque and built more like body on chassis. here are 2pics of my car, showing the ladder frame edges in front and back. I have seen nano's getting crushed in front (till windshield) at speeds less than 40kmph! but in all the cases I have seen so far, the cabin area is untouched.
In city I hardly get around 17kmpl (max) but on highways I get about 20kmpl - 25kmpl with ac+3people.
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Getting a car that delivers high mileage is easy - choose a lighter car, smaller engine and drive off peak hours. But consistent delivery of mileage is one thing that is not often missed out when deciding a car.
Maruti has managed to master this game, by consistently offering cars in and around 1000kgs mark and always making them a bit more tinny & lesser in weight than competition, apart from improved aluminium engines etc.
If I have to choose a car with mileage that stays same for a long time (assuming normal maintenance is taken care of) I would still go with Maruti anyday.
Real life example:
Even an average 10yr old esteem will still manage 10kmpl, when a good condition Ikon(say 5yrs old) struggles to deliver 12kmpl. All that good build quality and heavy spares, safety features hits the mileage on the long run.