Popular Mechanics - USA (2018-07 & 2018-08)

NO VEHICLE, not even your own feet,

can take you farther with less energy

than a bike. And when a bike has mul-

tiple gears—two or three chain rings up next

to your pedals and up to 11 cogs on your back

wheel—it makes riding even easier. And faster.

The size of the gears, and how they’re com-

bined, determines how many times the rear

wheel turns—and how far you travel—with

every pedal stroke. If you have your chain

on the smaller chain ring and it has 25

teeth, along with a rear cog of the same size

(in yellow, above), the wheels rotate once

for every pedal stroke. It’s a 1:1 gear ratio.

If you shift to your big chain ring, and it has

50 teeth, that’s a 2:1 ratio. Then every pedal

stroke makes the wheels rotate twice. And

if you shift your chain to a smaller cog in

the back, like a 13-tooth cog (in purple), you

get a 3.85:1 ratio. The wheels rotate almost

four times with every stroke.

A lower, easier gear, with the

smaller chain ring up front and

a larger cog in the back, lets you

accelerate faster. This helps you

get started from a stop, or when

you’re climbing a steep hill. The

higher, harder gear (big chain ring,

small cog) helps you increase your

top speed, but requires more

work and muscle to accelerate.

You also can’t always cruise

in the fastest gear because you

face resistance from wind and

your tires rolling on the road.

Those forces are trying to slow

you down and require accelera-

tion to maintain your speed. So

even if you’re not trying to go

faster, holding a constant speed

takes a lot of muscle and efort

because you’re in the largest and

hardest gear combination.

WHEN TO USE

DIFFERENT GEARS

How It Works

BIKE GEARS

“I hope kids out there get excited about the

new jet and study hard in school, especially

math and science. Before I thought about

being a pilot, I wanted to be an aeronautical

engineer and design things like this. Nobody

told me I could actually ly them. If you want to

do it, don’t let anybody tell you that you can’t.

Pursue your goals and make a plan.”

—Jim Less, deputy chief pilot, NASA. Less will be

the irst NASA pilot to ly Lockheed Martin’s new

(quiet) supersonic plane, called the Low-Boom

Flight Demonstrator. For more on the ground-

breaking aircraft, turn to page 2   .

FROM A SUPERSONIC JET PILOT

Expert Advice

25-tooth

cog

25-tooth

chain ring

50-tooth

chain ring

13-tooth

cog

ILLUSTRATION BY CHRIS WAHL

@PopularMechanics JULY/AUGUST _ 201 7