Episode 28: Postcards and Springs

This is moving season in Japan.
In the last few days, three of my friends have sent me postcards saying they’ve moved.

That reminds me, cars are supported by a size of about four postcards.
The area where a tire touches the ground is about the size of a postcard.

Tires are made of rubber, which of course has elasticity.

That’s why we fill tires with air, to use the air as a spring to absorb the shock from the road.

Motor vehicles use a variety of “air springs.”

Large vehicles use “air suspension.”
For instance, trucks and buses use it.
It looks like some high-end family cars are using it now, too.

Air gets elasticity when it is compressed.
High air compression makes a “hard spring,” and low air compression makes a “soft spring.”

In other words, air gives a lot of power to change the power of the spring that you don’t get in metal springs.
You may have occasionally heard a “psshh” sound as air comes out from a truck or bus—that’s the air pressure being lowered.

You normally don’t see the air damper, but imagine it as like a syringe.
It’s an empty syringe with no medicine.

By the way, there are also “oil dampers” that have viscous oil instead of medicine.
They are used in places that need to control stronger forces than air dampers.
For instance, they are used for seismic isolation underneath buildings.

Then there are even “gear dampers,” which don’t use air or oil, but gears, which introduce friction.

Gear dampers are used for the grab handles above the rear passenger windows of a car (though sometimes small oil dampers are used).
The grab handles slowly return to their original positions after being released because of the dampers.

Air dampers are also used for vending machine lids.
They make it so that the lid closes slowly after you get your drink out of the slot.
Wouldn’t it be annoying if no air damper was used and the lid made a big bang every time?

Let’s get back to the subject of tires.
Back in the old days, car tires used inner tubes.
Those would go flat all the time.

Car tires have been tubeless for about 30 years now.
Rubber tires are joined tightly on metal wheels so that air cannot escape.

Tires are really important.
They’re carrying cars weighing tons on contact areas the size of postcards.
And that’s true whether they’re stopped or moving.

When you drive around a curve, the car’s weight moves to the outside of the curve, but that movement force is absorbed by the deformation of the rubber and by the air pressure.

If a lot of air pressure is put in the tires, it becomes easy to pick up speed, but shock from the road comes through easily and makes the ride less comfortable.
With low air pressure, on the other hand, the ground contact area is bigger, so there’s more friction and it’s harder to pick up speed.
Compared to driving at 60 km/h on tires with high air pressure, if you shoot for the same speed with low air pressure, you’ll have to push the pedal further to overcome the friction, which uses a lot of gas.

Make sure you’re driving with the right air pressure for your car and its tires.

This is as far as I can go this time.

Before there were cars, aristocrats would ride horse-drawn carriages, but the wheels were wooden with metal plate for the ground contact surface, so it seems they weren’t all that comfortable.
The great Mozart went around Europe playing music with his father since he was three, but it seems he never liked traveling on carriages.

I sure am glad I was born when there were already cars!

See you next time!