Rocket and Raven look at two bikes side by side.
One has thin, smooth tires. The other has fat, bumpy tires.
"The fat ones look stronger," Rocket says.
Raven runs her eyes over the bumps. "What do you notice? Where would each bike ride best?"
Nova hovers between them. "Think about a dirt trail," she says. "Then think about a smooth road."
Road bikes usually have thin tires.
Road tires can be filled to 100 or even 120 PSI.
Mountain bikes have big, fat tires.
On a dirt trail, a fat tire floats on top of the rough ground.
A thin tire would sink into soft dirt.
Tread is the pattern on the outside of a tire.
Bumpy, knobby tread grips dirt trails better.
Smooth tires grip smooth roads better.
Smooth tires slip on dirt trails.
| Tire | Shape | Best place |
|---|---|---|
| road tire | thin and smooth | smooth roads |
| mountain tire | fat and knobby | dirt trails |
| Week check | True or false? |
|---|---|
| Air inside a tire pushes out on its walls. | ? |
| The safe pressure range is printed on the sidewall. | ? |
| A child should use the pressure gauge alone. | ? |
| Knobby tread grips dirt trails well. | ? |
Fantastic week, tire experts! Tomorrow is Bike Shop Day. Watch a grown-up check and pump a tire.