How to Buy a Kids' Bike

What size bike does your child need?

All experts say the most important consideration in choosing the right bike is size. The main mistake parents make is buying a bike that is too large, thinking that their child can grow into it. However, a poorly sized bike will cause frustration and will probably sit in the garage. Nearly every expert we found recommends taking your child with you to the store to ensure a proper fit. Sizing impacts how well your child can reach the ground, pedals and handlebars. If the bike is too large or too small, your child will have difficulty steering and braking. (Please also read our report on bicycle helmets.)

The size of a child's bike is determined by the diameter of the wheels, usually ranging from 12 inches to 24 inches. The wheels of adult bikes start at 26 inches. Experts say your child's age is an unreliable indicator because children grow at different rates. Measuring your child's height or inseam is the best way to find the right size.

Children's Bike Sizing Guidelines

David Fiedler, the About.com guide to bicycling, developed the above sizing chart for kids' bikes. Although some manufacturers make 18-inch bikes, they are less common, and most children move directly from a 16-inch to a 20-inch bike, depending on their height. While charts like these are helpful, experts say a fitting at a bike shop is the best way to determine the correct size, especially because different manufacturers use different age guidelines.

When the child tests the bike, the balls of both feet should be on the ground while sitting on the bike's seat and holding the handlebars. When straddling the center bar, both feet should be flat on the ground and there should be 1 to 2 inches between the child and the top bar of a boy's bike. Some girl's bikes have lower top bars -- called a step-through frame -- but it's still important that there is plenty of room between the child and the top bar.

The hub, spokes and rim of a wheel should all be metal. Some experts say steel rims and chrome-plated rims aren't ideal. That's because when wet, these metals create less friction between the rim and brake pad, which can make it more difficult to stop the bike. For children's bikes, aluminum or alloy rims are better for braking. Aluminum is lighter, stronger and more abrasive than steel. Aluminum rims reduce the amount of slipping in the brake system and make it easier to stop.

Children's bikes have coaster brakes, hand brakes or both. Coaster brakes are on the back wheel and are engaged by pedaling backwards. Experts say they are much easier for kids to learn to use. Hand brakes, according to the International Bike Fund (www.ibike.org), are "brakes engaged by a grip on the handlebars that pinches brake pads against the rim of the wheel." Bikes with 12- or 16-inch wheels usually have coaster brakes because of the limited hand strength of younger children, although we're seeing more kids' bikes with both coaster and hand brakes. The International Bike Fund also writes that, "When assessing the braking mechanism you want to make sure that it is stiff enough and strong enough to handle the weight and speed of the rider."

The following is what specialists say to look for in a children's bike:

• Size: Size and fit are not necessarily the same thing. On the books, kids' bike sizes are recorded based on wheel size, but frame design plays a big part in the fit of a bike. BMX frames, for example, can have different sizing than traditional frames, because the top bar of a BMX frame sits lower.

• Gears: Kids seem to be happy with fewer gears than adults. Although some advanced mountain bikes with 21 gears are marketed to children, the typical kid's mountain bike has six gears. Most bikes for younger children have only one gear.

• Shifters: Grip shifters are considered better than trigger shifters for two reasons: First, they require much less dexterity to shift from one gear to another; and second, they're harder to break when a child (who is usually much more prone to falls) crashes a bike.

• Graphics and colors: This seemingly frivolous consideration is actually so important that it's sometimes the defining element, at least as far as kids are concerned. The only difference between many boys' and girls' models is the gender-specific coloring. There is absolutely no technical reason why a girl could not ride a boys' bike or vice versa.

• Training wheels: Most 12-inch and 16-inch models come standard with training wheels. Make sure that the wheels are removable, so a child can have a good two-wheeler once he's mastered the balance required for biking.