Tire Lab teaching notes

About these lessons

Four lessons of about forty-five minutes each, for ages eleven to fourteen. Students carve a tire's tread, brake on a wet road and watch the water under the tire from below, get stuck in mud and sand and work out why, and hear the note a tire hums. Each lesson has one idea, ends with something the student did and can explain, and only uses what the lessons before it taught.

You do not need to have used Tire Lab before, or to know anything about tires. Everything you are asked to say or point at is written here, in the words that are on the screen. Every step in this guide has been walked through in the lab with real clicks, and is walked through again whenever the lab changes.

How to read this guide

Each lesson is a row of short parts, and each part has the same five headings:

1. Say what to tell the class, in a sentence or two. Use your own words if you like.
2. Students do the steps, in order. Read them out or put them on the board.
3. On their screens what you should see when you walk round. If a screen does not look like this, that student needs you.
4. If it goes wrong what usually goes wrong at this step, and the way out.
5. Ask a question for the room. The point is the talking, so take two or three answers and do not give yours.

The four lessons

Before the first lesson

• Every student needs Tire Lab open in a browser, with a mouse or a trackpad. It runs on a Chromebook. Nothing is installed.
• Work is kept as the student goes. There is no save button to forget.
• Lesson 4 needs sound: headphones are best. Everything else works with the sound off.
• The lab shows mph and feet, or km/h and meters. The two buttons on the Test bench switch between them. This guide gives numbers in feet; in meters they are about a third as big.
• Try lesson 1 yourself first. It takes ten minutes, and you will have met every button the class will meet.

The screen. These are the names this guide uses, and they are the words on the screen.

Lesson 1: Why tires have grooves

Lesson 1: Why tires have grooves: Brake on a dry road, then in the rain (0 to 10)

1. Say This is Tire Lab. Today you find out why every car tire has grooves cut into it, when a smooth one would have more rubber on the road.
2. Students do Open Tire Lab. Press Test at the top. Under Road, press Dry road, then press Brake. Watch the bottom picture. Then press Heavy rain and press Brake again.
3. On their screens A small car drives in from the left, the brakes go on at a yellow line, and it stops. On the dry road the lab says about Stopped in 102 ft from 50 mph. In heavy rain it stops about twice as far, and a dashed line says a dry road stops here.
4. If it goes wrong Nothing happens: the run takes a few seconds. Wait for the car to stop before pressing anything else. A student who sees meters has pressed km/h and meters; that is fine.
5. Ask The tire is the same and the car is the same. What changed, and why would water make the car need twice as far?

Lesson 1: Why tires have grooves: Look underneath (10 to 20)

1. Say The top picture is the part of the tire touching the road, seen from underneath, as if the road were glass. It is called the patch, and it is about the size of your hand. Everything a car does, it does through four of these.
2. Students do Press Brake again in Heavy rain, and this time watch the top picture.
3. On their screens Black blocks of rubber, and between them grooves full of blue water. At the start, a pale sheet of water covers the front of the patch, and the words under the picture say how much of the patch is on water. As the car slows down, the sheet shrinks.
4. If it goes wrong The picture moves too fast to see: it is already slowed down 120 times. Press Brake again and watch only the front edge.
5. Ask The blue in the grooves is water on its way out. Where does it go? Why does the sheet of water at the front get smaller as the car slows down?

Lesson 1: Why tires have grooves: A tire with no grooves (20 to 30)

1. Say If grooves are so good, why not more of them? Let us try the opposite first: a tire with none at all.
2. Students do Press Tread. Under Start from, press Smooth. Then press Test, press Heavy rain and Brake. Then press Dry road and Brake.
3. On their screens In heavy rain the smooth tire stops in about 430 ft, twice as far as the tire with grooves. The patch picture shows no grooves at all, and a big sheet of water at the front. On the dry road it stops in about 91 ft: shorter than the tire with grooves.
4. If it goes wrong The distances did not change: the student is still on the Tread bench. Press Test, and press Brake again.
5. Ask Racing cars use smooth tires on a dry track, and change them when it rains. Why?

Lesson 1: Why tires have grooves: Cut your own (30 to 45)

1. Say Now you are the tire designer. Start from the smooth tire and cut grooves into it until it stops as short as you can in heavy rain. Write down each change and the distance it gave.
2. Students do Press Tread. Check that Cut a groove and Line are picked. Drag across the big picture of the tread to cut a groove. Then press Test, Heavy rain and Brake. Go back and cut more.
3. On their screens The groove appears in the picture, in every pitch, and on the 3D tire beside it when the mouse is let go. A dashed blue box called on the road shows how much of the tread is on the road at once. Grooves that run off the side of the tread, or all the way down it, make the stop shorter. A groove that ends inside the rubber does much less.
4. If it goes wrong A cut went somewhere unwanted: press Take back the last cut. A student who has made a mess: Clear my cuts.
5. Ask Which of your grooves helped most? Why does a groove need to reach the edge of the patch?

By the end, each student can say:

• I braked in the rain and watched the water under the tire.
• I can explain why a smooth tire grips best on a dry road and worst on a wet one.
• I cut grooves that made a tire stop shorter in the rain, and I can say which helped most.

Lesson 2: Stopping distance

Lesson 2: Stopping distance: One change at a time (0 to 5)

1. Say Scientists change one thing at a time, so they know what did it. Today you change one thing about the tire, brake, write down the distance, and put it back before you change the next.
2. Students do Press Show all at the top right. Start from an ordinary car tire: on Kind check that Car is picked, on Tread press Blocks and Clear my cuts, and on Size press Put it back as it came. Draw a table with three columns: what I changed, to what, how far it took to stop.
3. On their screens Show all is outlined, and the Size bench has five sliders.
4. Ask Before you start: which do you think will matter most, a worn tire, a soft tire or a faster car?

Lesson 2: Stopping distance: A worn tire (5 to 20)

1. Say Tread wears away a little every time a car drives. Let us see what a worn tire does in the rain.
2. Students do Press Test. Press Steady rain. Move Speed when the brakes go on to 60 mph. Press Brake and write down the distance. Then press Size and move Worn away to 50%, then to 75%. Go back to Test and press Brake after each.
3. On their screens New tread: about 223 ft. Half worn: about 265 ft. Three quarters worn: about 323 ft. In the patch picture, the grooves are shallower and the sheet of water at the front is bigger.
4. If it goes wrong No Worn away slider: Show all is not on. Press it.
5. Ask Tire testers have measured this on real cars: a tire worn to the legal limit can need nearly twice as far to stop in the rain as a new one. Why does wear matter so much more in the rain than on a dry road?

Lesson 2: Stopping distance: The air in the tire (20 to 30)

1. Say Now put the wear back to nothing and change the air instead.
2. Students do On Size, move Worn away back to 0%. Press Test, then Heavy rain. Press Brake. Then on Size move Air pressure to 20 psi, test, then to 44 psi, test.
3. On their screens At 33 psi about 321 ft. At 20 psi about 428 ft. At 44 psi about 297 ft. On the Tread bench, the blue box called on the road grows longer as air is let out. The result on Test says the speed NASA's rule gives for this air.
4. If it goes wrong The distance changed more than expected: Worn away was not put back to 0%. Check it.
5. Ask A harder tire stopped shorter in the rain. Read the line about NASA's rule. Why would more air keep the water from lifting the tire?

Lesson 2: Stopping distance: Faster (30 to 45)

1. Say Put the air back to 33 psi. Last change: the speed.
2. Students do On Test, in Heavy rain, brake from 30 mph, then 60 mph. Then press Dry road and brake from 30 and 60 again.
3. On their screens On the dry road, twice the speed takes about four times as far to stop. In the rain it takes more than four times as far, and at 60 mph the patch picture shows much more of the patch on water.
4. Ask On a dry road, why does twice the speed need four times as far? Why is it even worse in the rain?

By the end, each student can say:

• I changed one thing at a time and kept a table of what each did.
• I can explain why a worn tire is worse in the rain than on a dry road.
• I can explain why going twice as fast takes four times as far to stop.

For students who finish early

With Show all on and a wet road picked, the Test bench has a box called Work out the water yourself. The student writes the rule the lab uses in the rain, from the numbers listed under the box, and the lab checks it against its own on six cases. It is real algebra: what share of the water is left, and what the speed does to its push.

Lesson 3: Off the road

Lesson 3: Off the road: The field after a storm (0 to 15)

1. Say Roads are only part of where tires go. Today the car leaves the road.
2. Students do On Kind, check that Car is picked. On Tread, press Blocks, and on Size, Put it back as it came. Press Test, then Course. Press The field after a storm, then Drive the course.
3. On their screens The car drives onto brown mud and stops almost at once. The lab says Stuck in section 1 of 4. In the patch picture, the grooves are light brown: packed full of mud. Under the results, the reason: the mud packs any groove narrower than it falls out of, and the tire turned into a smooth one.
4. Students do Press Tread, and under Start from press Lugs. Press Test and Drive the course again.
5. On their screens The grooves in the patch picture are dark: mud falls out of them. The lab says Made it to the end.
6. If it goes wrong The course changed to another one: a course button was pressed. Press The field after a storm again.
7. Ask The lugs tire has wide gaps that open at the side of the tire. Why would mud fall out of those, but not out of narrow ones?

Lesson 3: Off the road: The desert trail (15 to 30)

1. Say Sand is different. Put the tread back to Blocks and let us find out how.
2. Students do On Tread, press Blocks. On Test, press The desert trail, then Drive the course.
3. On their screens The car gets through the soft sand and the rocky trail, then stops on the sand hill: Stuck in section 3 of 4. The reason says the tire pressed on the sand too hard and sank into it.
4. Students do Press Size and move Air pressure to 20 psi. Press Test and Drive the course again.
5. On their screens Made it to the end. On the Tread bench, the blue box on the road is much longer: the same weight is spread over more sand.
6. Ask Park rangers on sandy beaches tell drivers to let air out of their tires, to less than 20 psi. Why does that help? And why do they also say to pump the tires back up before the road?

Lesson 3: Off the road: Things to try (30 to 45)

1. Say At the bottom of the Test bench is a list called Things to try. Each one is a tire to design. When your tire does one, it gets a tick.
2. Students do Open Things to try and pick one, such as A car across the field or Good at two things. Press its title to read it and a clue.
3. On their screens A green tick and the words This tire does it. as soon as the tire meets the goal.
4. Ask The mud tire got through the field. What did it cost? Look at its label on the Tread bench: grip in the rain, easy to roll, quiet, and how long it lasts.

By the end, each student can say:

• I got a car stuck in mud and through it, and can say why the new tread worked.
• I got a car up a sand hill by changing the air, and can say why it worked.
• I can name something a mud tire is worse at.

Lesson 4: The sound of a tire

Lesson 4: The sound of a tire: Listen (0 to 10)

1. Say Put your headphones on. A tire hums as it rolls, and in a car you stop noticing. Today you find out where the hum comes from.
2. Students do On Tread, press Blocks. Press Test, then Brake test, then Dry road. Check that Hum on is picked. Press Brake and listen.
3. On their screens A high whine that falls lower and lower as the car slows, and stops when it stops.
4. If it goes wrong No sound: the computer's sound is off, or Hum off is picked.
5. Ask The note fell as the car slowed down. If each block makes one tap, what would make the taps come closer together?

Lesson 4: The sound of a tire: Three lengths (10 to 25)

1. Say A tire's tread is one pattern, called a pitch, repeated all the way round. If every pitch is the same length, the blocks tap at a perfectly even beat.
2. Students do Press Show all if it is not on. Press Tread. Under Round the tire, find All the same and Three lengths. Read the line called The hum in the table under What the tread does, and the grade called Quiet in Its label. Then press Three lengths and read them again. Go to Test and listen to each.
3. On their screens With all pitches the same, about 85% of the hum is on one note and Quiet is B. With three lengths, about a third of it is on one note and Quiet is A. It sounds more like a rush than a whine.
4. Ask The tire taps the road just as often either way. Why does it sound quieter?

Lesson 4: The sound of a tire: Your own order (25 to 45)

1. Say Tire makers choose the order of long, medium and short pitches carefully, and some of the orders are patented. Now you write one.
2. Students do Under Round the tire, press My own. A box appears with a program in it: one line for each pitch, long, medium or short, and repeat 4 times { round some of them. Change the program and watch The hum. Try to get less of the sound on one note than Three lengths did. Press Blocks under the box to see the same program as blocks.
3. On their screens Under the box, a line saying how many pitches the program makes and how many the tire has. The hum changes as the program changes.
4. If it goes wrong A line in orange saying what is wrong and on which line: usually a repeat with no } to close it. The tire keeps the last program that worked.
5. Ask What order gave the least sound on one note? Is it a pattern you could describe, or did it look random?

By the end, each student can say:

• I heard the hum fall as the car slowed, and can explain why.
• I can explain why pitches of different lengths make a tire quieter.
• I wrote my own order of pitches and measured what it did.

Where to go next

Tire Lab has more for students who want it. On the Test bench, Rally season asks them to write pit rules for ten stages with forecasts that are sometimes wrong, and compares them with the best a crew could do. On Tread, the Code start builds a tread from a formula. On Export, A tire to print makes the tire as a file for a 3D printer, to print in flexible filament for a robot or a small car. Each of these can be a lesson in the same shape as the four here.

More help

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