A post in which we learn of power, weight, aerodynamics and rolling resistance.

In the course of this month, I hope to have travelled in two very different vehicles.

Here’s one.

It’s a 1.2l K12 Nissan Micra. It has 80 bhp and fortuitously weighs almost exactly a tonne so we can easily calculate that it has 80 bhp/tonne to play with.

Here’s the other.

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It’s a TGV train, pictured at the Gare de l’Est in Paris which is just where I hope to pick it up. It has 12,900 bhp, which is a lot but then it weighs about 383 tonnes so 34 bhp/tonne. Incidentally, it would take about four diesel locos to give this much power at the wheels and that wouldn’t be near enough to match it performance-wise because they’re much heavier (I must work out sometime just how many you’d need) EDIT: You couldn’t practically use diesels and get the same performance.

Now rhere’s the thing. The train runs at up to 300 kmh and could manage 320 where allowed. The Micra, with more than twice the power per tonne, can barely manage half of this speed. If you could get the Micra up to 300 with less than 400 bhp I’d be surprised.

What do we conclude? A small frontal area in relation to the overall size of the vehicle plus lower rolling resistance can do an awful lot for performance.