Do you know why a tiny Alto K10 can outrun a Mahindra Scorpio?

An Alto K10 can beat a Mahindra Scorpio – but not always!

Most car enthusiasts would know the answer to this one straight away. It’s simple physics. In other words, it’s because of power-to-weight ratio. Is this something you, the car buyer, need to consider?

power to weight ratio explained

Yes it is. Because all those numbers of torque and bhp that carmakers spew do not necessarily mean that more bhp or more torque makes for a faster car. And that’s precisely why a puny little Maruti Alto K10 with a 1-litre, three-cylinder engine that puts out just 67 bhp of power can comprehensively outrun a Mahindra Scorpio with a beastly 2.2-litre four-cylinder diesel engine that puts out 120 bhp of power.

So when you look up the specifications of a car, don’t get fooled by the numbers. Sometimes the smaller, innocent looking hatchback can be a much faster or more powerful car than that big burly SUV you’ve been thinking of.

It’s the same reason Formula 1 teams spend millions of dollars in making their cars lighter, and slamming diets and gym routines on their drivers. Power-to-weight ratio is a key factor that differentiates the performance of one car from another.

Power to weight ratio is the key

Here’s how you calculate the power-to-weight ratio of a car:

  • Look at the car’s power output (bhp figure).
  • Look at the cars’s kerb weight (unladen weight).
  • Divide the power output by the kerb weight.
  • Multiply the figure by 1000 to get the bhp-per-ton figure.

This bhp-per-ton figure is what is crucial to the car, and will show you how quickly the car can accelerate or reach its top speed. Lighter the car with more power, higher the power to weight ratio will be.

Getting back to the example of a Maruti Alto K10 and a Mahindra Scorpio, you will find that the Alto has a power to weight ratio of 88.15 bhp per ton (with a kerb weight of just 760 Kg) while the Scorpio just puts out 64.86 bhp per ton (as it has a massive kerb weight of 1850 Kg).

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Observe how an Alto K10 can accelerate out of a traffic light and you’ll see this power-to-weight ratio at play. Of course, over a long haul the larger capacity engine can catch up, but it takes time.

Torque changes the game!

But which of these two would be better at climbing a hill from a standing start or carrying a heavy load? In such situations torque plays a major role in getting a vehicle to start moving from standstill. The more torque an engine generates the easier it is to get the car moving.

Here diesel engines have an advantage because of the higher torque they develop compared to petrol engines. If you look at the torque figures of the above two vehicles, the Alto K10 makes just 90 Nm of torque at 3500 rpm while the Scorpio puts out 290 Nm at 1800 rpm. What this means is that you have to rev the car to the specified rpm figure to squeeze the maximum torque or pulling power out of the engine. You’ll notice this figure is much lower for diesel engines, which therefore makes them inherently better for load carrying applications and places where heavy duty running is needed.

When you look at the torque per ton figures available, the Alto’s figure is only 118 Nm per ton, while the Scorpio, despite its massive kerb weight puts out 157 Nm per ton of torque, making it easier for the Scorpio to get up a hill from a standing start than an Alto K10 can.

So while you are out shopping for a car, don’t just go by the numbers carmakers put out there. Look at the power-to-weight ratio and it will give you an idea of which car is faster (and sometimes even more fuel efficient).

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