# TRICKY TYRES

From a swanky Corvette to a dusty goods Carrier, tyres remain the indispensable underdogs of the automobile industry. But are they merely the dusty, worn-out rubber-tubes fixed atop a metallic ring that we see?

Let’s take up the case of a bus. A standard, functional, long wheelbase vehicle, with big tyres and high loading capacity. But when you take a closer look, you’ll notice the peculiar way the tyres have been arranged.

Why do you think, are the wheels not placed at the extreme ends? The answer to this, my friend, is the sorcery of science.

In a bus, or in any given vehicle, the tyres are placed in such a way that they enhance the vehicle’s loading capacity as well as its stability. Technically speaking, what we need is an arrangement that offers the minimum shear force and bending moment. That is, your good ol’ bus should be built such that it doesn’t break and bend out of proportion, when you and your friends and your best friend’s third cousin’s maternal uncle’s son joins you for a bus ride.

Take a look at a crude representation of the same – an ordinary beam carrying an equally distributed load. The trick now, is to place the supports in a way so as to maximize the stability of the entire structure. In other words, we need our good ol’ beam to hold strong and sturdy in the face of passenger overload.

Where do we start from? From the extreme ends, of course. We place our supports at the extreme end points of the beam and call up an engineer friend to do the necessary calculations. Now, we have our initial and default values of shear force and bending moment to work with. These values give us the end point of the endurance of our bus.

Let us move the two supports towards the center of the beam and call up the friend again to do the calculations for this new arrangement. We now, have our second set of values to compare with the default ones.

You will notice that there is a significant difference between the two values and apparently, the second structure is a lot more stable (and not prone to break down in rush hour traffic) than the first one.

Science hath spoken!

Oh, there is more. After all, your bus is more than just a beam standing atop two non-circular supports. When designing a vehicle, especially something as vital to public transport as a bus, automobile engineers also have to take into account where the engine is placed (in the rear or the front), the seating arrangement (so that the entire load is evenly distributed), as well as the turning radius of the vehicle. Given the close corners and narrow turns, we would want our buses to be easily steered around the crowded street corners.

They say that a tyre by any other name would roll just as fine. Or would it? Go figure.