Bicycle Size: A Guide to Wheels and Frames for Sizing

When buying a bike, choosing the right bicycle size is the most important factor you need to get right. The right sized bike makes riding comfortable and easy. Especially when it comes to children’s bikes, sizing is what makes the difference between comfortable, smooth riding and accidents and unhappiness.

Let’s take a look at a sizing guide.

As a general rule, the larger the wheels, the more that the frame size becomes a factor. Adult bikes are sized by their frames and children’s bikes are sized by wheels.

Find the right size bike for your child

Children’s bikes are measured by wheel size. The smaller the wheels, the lighter the bike and the easier it will be for the child to ride. However, smaller wheels will be quickly outgrown and become cramped and uncomfortable.

Finding a good balance between light wheels and wheels with a little room to grow, is crucial for picking a bike that will last.

The Best Toddler Bicycle for your kids

Children’s bikes range from 12 inch wheels to 26 inch wheels.

Usually children’s bike sizes fall into categories that match their age. However, you should choose whichever bike is the best fit for your child, even if it’s not in their official age category.

Your child should be able to sit comfortably on the bike and be able to reach the handlebars and brakes easily and their feet can touch the ground properly, then go ahead and buy the bike even if it’s not in your child’s age group.

16 inch wheel bikes are generally for children who have graduated from using stabilisers. This is usually about the age of five years old. However, if your child needs a 16inch bike and also needs the stabilisers, they can usually be fitted to most 16 inch bikes.

From 20 inches, children’s bikes come in different frame sizes, which is great because it means you can put a younger child onto a 20inch wheel bike, if they are a confident rider and ready to make the jump.

You may need to shop around for different models because not every bike will come in every wheel and frame size.

Once your child is ready for a 26 inch bike, they are riding an adult bike and these are measured in frame size only.

Check out this handy chart to help you determine frame sizes for your child’s bike.

Choosing the right child bike

Choosing the right-size bike for an adult

The best way to find the right sized bike for you, is to sit astride it and make sure that your feet can comfortably touch the ground and you can also reach the handles and brakes easily.

If you’re buying a bike online, there’s a easy way to measure the correct bike size, even when you can’t try the bike yourself.

Adult bikes are measured by frame size. The frame is generally measured from the centre of the crank axle, to the top of the seat tube. Most road bikes are measured in centimetres whilst mountain bikes are generally measured using inches.

The two main measurements you will need are your height and the inside seam of your leg. You can measure your height with a friend and a tape measure or if you’re on your own, stand up straight against a wall and make a small pencil mark on the wall level with the top of your head.

Then you can use a measuring tape to find out how tall you are. Make sure to take your shoes off so you get the correct measurement!

To measure the inside seam of your leg, stand with your legs slightly apart and either have someone measure it for you, or make a pencil mark against a wall and use a tape measure to measure it yourself.

The inside leg seam measurement ensures that the standover height of your bike is correct. This means the distance between the top tube of the bike frame and the ground. Ideally you should add an extra inch for road bikes and 3 inches for mountain bikes so that you will be fully comfortable.

Once you’ve worked out the correct height, you should start thinking about the length. This refers to the distance from the saddle to the handlebars. Women’s bikes are built for shorter upper body length and so the distance from the saddle to the handlebar is less than on a man’s bike.

As the frame increases by every 2 inches, so the length increases proportionally by about 1 inch.  However the saddles on all bikes are adjustable so you should be able to tailor the bike to suit your body length perfectly.

Wheel size will depend on whether you want a road bike or a mountain bike. If you’re buying in a bike store, someone should be able to check that your bike is the correct size, and you can then ask about tyres.

It is important to note that you can always change the tyres, the most important point is to find the correct size bike, even if it doesn’t have the tyres you want. You can always change the tyres later.

For a quick reference

Racing Bikes: You should be able to stand with your feet flat on the ground and have about 1 inch free between yourself and the top tube of the frame, adjust the saddle if necessary. Check you can reach the handlebars comfortably.

Mountain Bikes: You should be able to stand with your feet flat on the ground and have at least  3 inches of space between yourself and the top tube of the frame, adjust the saddle if necessary. Check you can reach the handlebars comfortably.

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