Boys and bicycles seem to be as classic a combination as apple pie and ice cream. They spend endless hours pedaling and playing on their two-wheeled transports. Like adults, boys need a properly sized bicycle for safety and performance. Getting a bicycle sized properly depends on the boy's age and height. Once the bicycle is purchased in the appropriate size, your boy can head out for healthy pedaling fun.
Measure your boy's inseam. The inseam is used to determine the wheel size of the bicycle -- the proper size measure in children's bicycles.
Have the boy sit on the bicycle while you or a bike shop employee holds the front wheel and handlebars steady. Have the boy move the pedals so that they are at equal heights from each other. Look to see if there is a bend at the knees.
Let the boy slowly move the pedals about 180 degrees, with one up and one down. Look at the lower leg to make sure it is not fully extended. The boy's leg should have a slight bend at the knee.
Get the boy to stand over the top tube of the bicycle -- the tube that runs from the handlebars to the seat stem. Make sure the boy's crotch has one inch or more of clearance off the frame.
Use the following as a general starting point for the boy's sizing:
Select a 12-inch-wheeled bike for boys between 2 and 4 years of age with an inseam between 14 inches to 17 inches; a 14-inch-wheel bicycle for boys age 4 to 6 years with inseams between 16 to 20 inches; a 16-inch-wheeled bicycle for boys age 5 to 8 years with inseams between 18 to 22 inches; an 18-inch-wheeled bicycle for the 6 to 9 year age group and inseams between 20 to 24 inches; a 20-inch-wheeled bicycle for ages 7 to 10 years old with inseams between 22 to 25 inches; or a 24-inch-wheeled bicycle for boys 9 years old and up with inseams between 24 to 28 inches.
Make sure your boy gets a helmet to go with the bicycle to prevent head injuries.