Bike Shop
Gear ratios are usually taught with tooth counts on paper, and bike repair is taught in a shop with ten students and a mechanic. Bike Shop puts both on a Chromebook. A customer brings in a bike with a complaint. The student finds what is wrong, fixes it and tests it. On the Gears stand the fix is a ratio. On the other three it is a diagnosis: a cable, a spoke, a thorn still in the tire.
Using this with a class? Make a free class and add your students yourself: each gets a username and password, with no email or Google account needed. Or give them one join code. Using Google Classroom? Post the link there; with a free class, the link also puts each student in your class, so you see their work. mytekDev is also available from the Google Workspace Marketplace, so your school's Google admin can install it for everyone.A first lesson: One period for ratios: pedal one turn in two gears and compare the chalk marks, then close the hill tickets by finding the gear where the legs turn at a comfortable pace. A second period for troubleshooting: a derailleur whose cable has gone slack, a wheel that rubs, a tire that went flat again.
Set up a free class Share to Google ClassroomWhat a student actually does
The shop has a job board of twenty tickets and four stands. Each ticket is a bike with a complaint in the customer's own words: "I can barely push the pedals around on the hill by my school." "I click the shifter and nothing happens." "The brake goes shh, shh, shh, once each time the wheel goes around." "I put a new tube in on Saturday. It was flat again by Monday." A ticket closes when the bike passes its test, and the test reads the bike, not the clicks.
On the Gears stand a rider sits on one of three bikes on a road with a ruler painted on it. The student picks the chainring and the cog by their tooth counts and presses Pedal one turn. The crank goes around once, the bike rolls, and a chalk mark stays on a ruler across the top. 32 teeth to 20 rolls 3.06 meters. 32 to 14 rolls 4.37. Then the road tilts. A ride ends one of four ways: the pedals stop, a slow grind, comfortable, or spinning out. The hill by the school is comfortable in the 22 tooth cog, at 66 turns of the pedals a minute. A gear chart lists every gear on the bike from easiest to hardest, and on the bike sold as 24 speeds it counts 17 different ones.
The Shifting stand shows the back of the bike from behind: seven cogs, the chain, and the guide pulley that leads the chain onto a cog. The student clicks the shifter and turns three things a quarter turn at a time: the barrel adjuster and the two limit screws. A test ride shifts up through every gear and back, then pushes on both stops by hand. The Truing stand is a wheel with 32 spokes beside three strips that show, spoke by spoke, how far the rim sits to one side, how far in or out, and how hard each spoke pulls. On the Flats stand the student takes the tube out, finds the hole, checks the tire and the rim strip, patches or replaces the tube, pumps to a pressure inside the range on the sidewall, and names what caused the flat. A new tube over a thorn that is still in the tire goes flat again on the test ride.
A Shop report asks nine written questions about the work. Setup lets a teacher choose the questions, add their own, and open an answer key.
The ticket says "I click the shifter and nothing happens." The shifter is on the 16 tooth cog and the chain is still on the 14. The cable has gone slack, so each click pulls the pulley a little less than one cog. The fix is the barrel adjuster, a quarter turn at a time. The two limit screws will not help, and the student can try them and see.
One loose spoke. Spoke 9 goes to the right side of the hub and is not pulling its share, so the spokes on the left have pulled the rim their way. The three strips are the rim unrolled: tighten spoke 9 a quarter turn and all three move at once.
What they are learning while they work
Nothing here is presented as a lesson. This is what the activity is made of.
| What the student does | What it is |
|---|---|
| Counts 32 teeth on the chainring and 20 on the cog and reads that the wheel turns 1.6 times for each turn of the pedals | Ratio and unit rate. The gear is the ratio of the two tooth counts. Wheel turns for each pedal turn is its unit rate, and meters for each pedal turn is that rate times the distance around the tire. |
| Pedals one turn in two gears and compares the chalk marks on the ruler | Proportional relationships. Distance is the meters per turn times the number of turns. Changing the gear changes the constant. Half the cog teeth rolls exactly twice as far. |
| Finds 48 teeth to 24 and 28 teeth to 14 on the gear chart and pedals one turn in each | Equivalent ratios. Both are 2 to 1, so both roll the same 4.34 meters. A bike sold as 24 speeds has fewer different gears than that. |
| Rides the same hill in a high gear and a low gear and reads the same speed with different leg speeds | Force and distance trade. A gear never changes the work a hill takes. A low gear moves the bike a shorter way on each turn, so each turn takes less push and there are more of them. |
| Turns a limit screw, sees nothing change in the middle gears, then turns the barrel adjuster and watches the pulley move | Troubleshooting, one change at a time. Each control does one job. The cable sets where the pulley sits on each click. The two screws are stops at the ends. Changing one thing and testing again shows which part is at fault. |
| Tightens one spoke and watches the rim move toward that spoke's side, in toward the hub, and the spoke's pull rise | A system with tradeoffs. Spokes only pull. Every quarter turn changes three things at once, and a wheel is true only when the side to side, the up and down and every spoke's pull are all inside their limits. |
| Reads the hole in the tube before fixing anything: one hole facing the road, one facing the rim, two slits side by side, a cut at the valve | Evidence and cause. Each cause leaves its own mark. The repair only lasts if the cause is found and removed, and the ticket only closes when the student names it. |
How to tell whether it landed
Ask, and let them show you. A student who has understood it can answer these without help.
- A bike has 36 teeth on the chainring and 12 on the cog. How many times does the back wheel turn for one turn of the pedals?
- Your bike rolled 2.78 meters on one turn of the pedals. How far does it roll on 10 turns? What would you change to make that number bigger?
- A low gear makes a hill feel easier. Is the hill less work in a low gear? Explain.
- The chain is slow to climb to the bigger cogs. Which part do you turn, and why is it not one of the limit screws?
- The rim rubs on the left at one spot. What are two ways to move it back?
- A tube has two small slits side by side and nothing sharp in the tire. What happened?
Use it in your subject
Not a technology class? Then the app is how students show what they learned in your unit. More projects for every subject.
Grade 6 and 7 math
CCSS 6.RP.A.1, 6.RP.A.2 and 6.RP.A.3 for ratio language, unit rate, constant speed and converting units, and 7.RP.A.2 for a proportional relationship and its constant: distance equals meters per pedal turn times pedal turns, with a different constant in each gear. 7.G.B.4 for the distance around the tire.
Technology and engineering
ITEEA Standards for Technological and Engineering Literacy, STEL-8I: use tools, materials and machines to safely diagnose, adjust and repair systems. NAEP Technology and Engineering Literacy D.8.17: diagnose a problem in a technological device using a logical process of troubleshooting.
Grade 5
The Gears stand by counting turns, and the Flats stand. NGSS 3-5-ETS1-3 fits in part: fair tests in which one thing is changed and failure points are considered.
Science
NGSS has no performance expectation about troubleshooting, so this page does not claim one for middle school. The Gears stand supports a simple machines or forces unit as an example of trading push for distance.
Practical notes
- AgesGrades 5 to 8, and useful in high school technology courses. A middle school level uses plain words and the numbers a 6th grader uses. A high school level adds watts, the push on the pedal in newtons, millimeters at the derailleur and spoke tension in kilograms-force.
- TimeOne period for the Gears stand and its six tickets. One period for Shifting. One for Truing and Flats together. The Shop report takes fifteen minutes.
- EquipmentA computer or Chromebook with a modern browser. Nothing to install, and no bike needed. Headphones if the class is using the sounds.
- CostFree. The app has no paid tier.
- PrepAbout fifteen minutes: close the ticket Stuck on the gentle hill and the ticket Clicks but does not climb yourself, then open Setup and read the answer key.
- In a groupOpen Setup in the app's header to choose which of the nine questions are on the Shop report and to add up to ten of your own.
For co-ops, microschools, and classrooms
Set the Shop report up once in Setup and hand the project out as the starter; the setup travels with it. Every number is worked out from the bike, so two students in the same gear on the same hill read the same speed, and a class can argue from the same data. One rider does every ride, so the gear is the only thing that changes. If there is a real bike in the room, count its teeth, pedal one turn beside a tape measure, and compare with the app.
Common questions
Is it free?
Yes. Bike Shop has no paid tier, and it can be tried right on this page without an account.
Is the gear math real?
Yes. The ratio is the chainring's teeth divided by the cog's teeth, and the distance for one pedal turn is that ratio times the distance around the tire. The tooth counts are real parts: a 14 to 28 tooth 7 speed freewheel, and chainrings of 32 teeth, 24-34-42 and 28-38-48. The tire sizes are within about 1 percent of published tables.
How real are the rides?
The force on the road is the standard one: the slope, the tires and the air. The rider is made up: 45 kilograms, holding 75 watts, comfortable between 60 and 95 turns of the pedals a minute, sitting down the whole time. This rider puts out the same effort in every gear. A real rider loses some at a slow grind and can stand up on the pedals. One rider for every ride is what makes the gear a fair test.
How real is the repair?
The way each part behaves follows bike shop practice: the barrel adjuster sets the cable, the limit screws are stops, tightening a spoke pulls the rim toward its side of the hub, and each cause of a flat leaves its own kind of hole. The derailleur is one common 7 speed kind. How far one turn of a screw moves things, and how far off the chain can be before it ticks, are made up to behave like a real one. The wheel is a simplified front wheel. A rim bent by a pothole usually cannot be trued straight and needs replacing.
Does it teach brakes?
No. Brakes are left out on purpose: a wrong brake lesson is a safety problem. The app says so, and tells students to have a bike mechanic check real brakes.
Can a student fix a real bike after this?
They will know what each part is for and what to look at, which is the hard part to learn from a video. They will not have the feel in their hands. The app tells students to keep fingers away from the chain, cogs and spokes while anything is turning, to ask an adult before adjusting a real bike, and to check that both brakes work before riding it.
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Where to go next
Start with Bike Shop
Trying it costs nothing and takes about five minutes. An account is what makes the work last.
Bike Shop is one of the making apps on the platform. The stands are drawn in code and every result comes from the bike on the stand, so the same gear reads the same on a fast laptop and a slow Chromebook, and the app's test suite checks that every ticket can be closed and only by a bike that is right.
Page last reviewed November 2026.
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