Buying a diesel car might seem to be the smarter thing to do but more often than not it will take you many years to recover the initial extra that you would have paid for it. So, the basic premise should be to go in for a petrol car and then depending on the number of kilometres you drive every month switch to a diesel-engined car. We presume that you will drive the car for a minimum of five years and that you should be able to recover the extra money you have paid for the diesel vehicle in at least three years.

To illustrate the point, let's take four cars from different segments. Starting with the Ford Figo, the diesel version of the same variant costs Rs 89,500 more. To recover that amount, given a particular price of fuel (we have taken fuel prices in Delhi on September 1, 2015), one would have to drive the diesel car a minimum of 1,593 km every month for the next three years.

If you notice, this is not only dependent on the purchase price of both the diesel and the petrol car, but the cost of both diesel and petrol fuels as well as the real-world fuel efficiency of both the cars; the latter figure is from our road tests. Therefore, this figure will vary from car to car and also whenever the price of either diesel or petrol fuel changes.

While in the case of some cars such as the Toyota Corolla Altis, the switchover mileage per month is just 1,072 km, in the case of others such as the Skoda Superb, it can be as high as 4,603 km per month. The figure is so low in the case of Toyota because the diesel engine is much smaller and has much higher fuel efficiency than the petrol-engined car. In the case of the Superb, the diesel engine is in fact larger than the petrol engine and does not enjoy the fuel efficiency advantage.

It goes without saying that in the case of the Corolla Altis, if you make the switch you will be losing out on performance. But it's a very different case with the Hyundai Verna. Although both the diesel and petrol engines have a similar displacement and similar power, the diesel engine is still more fuel efficient even if not to the extent as the Corolla Altis diesel. Therefore the switchover mileage is much higher at 2,064 km per month for three years.

While we are making it sound very simple right now, there are other factors at play. Diesel cars are usually more expensive to maintain and repair, while there is also a cost that you will pay extra if you are going to buy a diesel variant.

Or if you are going to take a loan to buy the car, then to buy a diesel variant there would be an increased EMI, which may or may not be as much as you would be paying extra for running the car on petrol.

And then, there is also the comfort factor. Would you rather drive the noiseless and totally vibration free petrol-engined car or the slightly noisier diesel? Even though diesels are much quieter than before, and the high-end cars are well insulated, low-end cars can still be noisy. And finally, do you love bottom-end grunt or top-end performance? That's another choice that you will be making. As they say, the devil lies in the details.