GET IN THE RIGHT GEAR!
Parents
Take a bike ride and use math to find out how to bike more efficiently.
You’ll Need:
1 multi-gear bicycle
bike helmet
pencil and paper
optional: calculator
Duration:
30 minutes to an hour
What to Know:
If you’ve ever biked up a hill, you know it can be
pretty tough unless you’re in the right gear. Bikes
are designed with a gear system to make pedaling
more efficient depending on your terrain. The gear
ratio measures how many pedal strokes are required
to turn the wheel. With a high gear ratio, you pedal
fewer times to make the wheels turn and travel
much farther as a result. For example, a gear ratio
of 4 means for each pedal stroke, the wheel turns
4 times. A lower gear ratio results in you pedaling
much more often to turn the wheels, but it's what
makes climbing a hill feel like a lot less effort! Turn a
family bike ride into a mathematical investigation of
gears so you will never be in the wrong gear again!
Here’s How:
1. Make sure the bike is standing securely or flip it
upside down so you can study the gears. Count the
number of teeth on the gear in front (where the
pedals connect). Use the middle gear if you have
3 gears in front. Then count the teeth on both the
biggest and smallest gears on the back wheel.
Record these numbers.
2. Together, calculate and record the gear ratios for
each combination using the following formula:
Gear ratio = number of teeth on front gear
number of teeth on back gear
Record your numbers in a table like the one shown
below.
3. The gear ratio is what makes it easier or harder to
get up a hill. Figure out which is which! Have
everyone strap on a bike helmet and compare the
two settings by riding the bike up a small hill, first
set at the higher gear ratio and then at the lower
gear ratio. Which is harder to pedal in? Easier?
4. If you have more than one gear in front, calculate
the ratios for another set of gears. How do the two
sets of gears relate? Can you calculate the absolute
lowest and highest gear ratios for your bike?