Q: Why do bicycles fall over?
A: Because they are two-tired!

Explanation: Bicycles have two tires, that is, they have two wheels.  If a car is four-tired (has 4 tires) then you could say a bike is two-tired (has two tires), although no one would actually say that- except in a joke.  This joke plays on the words “too tired.”  If you are very tired, too tired, you have no energy.  Maybe you would fall over like the two-tired (too tired) bike!

Get some rest!