Appropriate grades or age groups:
6-12

Estimated time to complete this project:
10 hours

Materials:
Bicycle
(1 or more)
Air pump,guage,tape measure, duct tape, bike speedometer or stopwatch

What is the hypothesis of this science project? What does the experiment aim to prove?
Measuring and comparing one or more aspects of how to make a bike more efficient.
Sample comparisons:
Fat, nobby tires v. smoother thinner tires
High pressure v. low pressure in the tires
Sitting high up v. leaning over (wind drag)

Instructions:
Experimenter finds a slope (paved preferable) with low or no traffic
Bicycle and roder roll down a measured distance (100-500m)
and measure the time.
Different variables like mtn bike v. road bike, thin v. fat tires, varied air pressures, upright v. leaned over (road racing position)

Other comments or suggestions:
Kids actually understand what they are doing. They learn how riding distances can be easier (proper air pressure, change of position) without spending more money on bike equipment.
The efficiency regarding better, higher presure tires and more aerodynamic profiles can apply to energy saving with motor vehicles.
We only did the air pressure comparison.
Good Luck, have fun