## Exercise 2.4: Speed Ratios on a Mountain Bike Exercise 2.4

Speed Ratios on a Mountain Bike In this activity you are going to get out your mountain bike and calculate the speed ratio of the different gear combinations. If you don't have a mountain bike ask a friend to bring their bike over - they can even help you do your project!

Procedure:

1. First number the front sprockets 1(the largest), 2, and 3 (the smallest).
2. Now count the number of teeth on each sprocket. Record your results.
3. Now do the same for the back sprockets.
4. Fill the data you collected into the table.
5. Calculate the speed ratio where each front and back sprocket intersect in the table.

Calculate the speed ratios for mountain bikes with the following characteristics:
 Number of teeth on the Sprockets on the Back Wheel Front Sprocket #1 - 48 teeth Front Sprocket #2 - 36 teeth Front Sprocket #3 - 28 teeth a - 27 teeth speed ratio= speed ratio= speed ratio= b - 24 teeth speed ratio= speed ratio= speed ratio= c - 21 teeth speed ratio= speed ratio= speed ratio= d - 16 teeth speed ratio= speed ratio= speed ratio= e - 14 teeth speed ratio= speed ratio= speed ratio=

Analysis:
 1. Were most of the gear combinations multiplying gears or reducing gears? 2. If you could only see the calculated speed ratio data, how could you tell the difference between multiplying gear trains and reducing gear trains? 3. Explain what you think the terms 'high' and 'low' gears mean. 4. What sprocket combination would you start with in the following situations: a. Starting off on an ordinary flat street. b. Climbing a very steep hill. c. Going as fast as you can on a flat, straight road.