Selecting Your Bicycle Frame Size

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Buying Your First Bike: Choosing a Frame Size

If you are new to cycling the prospect of buying a bike can be a daunting one. There are so many options including frame size and bicycle types on offer that you can be paralysed sorting through the volume of information available and end up buying a bike that isn’t what you really need. We decided to create a Beginner Series here at online-bikes-co-uk to clearly answer the questions you may have so that you can buy a bike that is the correct fit for you.

The first thing to look for when buying a bike is the correct frame size. While most people of average height can ride most bikes comfortably, with minor seat adjustments, it is always better to carry out a few simple measurements and go with a frame size that suits your body. The wrong frame size can cause discomfort over a period of time, and will almost always result in peddling in an inefficient manner. It’s far better in the long run to take the time before you purchase a bike to make sure you have accurate measurements that are really very simple to do.

What is the correct frame size?

The correct frame size for you is one where you can sit comfortably on the bike, and when setting the pedal at the lowest point, your leg is completely extended and you are able to touch the ground with the tips of your toes. You also want to have a 1 inch clearance between you and the top tube of when straddling the frame. So other than sitting on lots of different bike sizes, how can you find out what size of frame is right for you?

Taking Accurate Measurements

The easiest way to discover the correct frame size for you is to measure your inside leg. To do this you should stand barefoot with your back against a wall. Then with your feet 6 inches apart, place a hardback book between your legs with the spine of the book facing upwards. Make sure the edge of the book is against the wall, and then slide it up firmly into your crotch. This simulates the bike seat.

Then have a friend measure from the spine of the book to the floor. If you would rather take the measurements yourself, using a pencil, leave a small mark where the spine of the book meets the wall, and then measure from the mark on the wall to the floor. Take these measurements three times, starting from the beginning each time, and then take the average as your inseam length. Make sure you take these measurements in centimetres.

Choosing the Frame Size

With your inside leg length measured you now need to apply this to the frame sizes using a simple formula to choose the correct one. Take your measurement and multiply it by .67. This gives you the measurement for road bike frame sizes measured from centre to top. So, if for example your inside leg length is 87 cm, then the calculation would be 87 x .67 = 58.29 cm. With this measurement you would fit a frame size for a road bike around 59cm. For mountain bikes you need to subtract 10 cm from the road bike frame size. In the previous example that would mean you are looking for a mountain bike frame size of 49cm or 19 inches.

Refine Your Choice

This formula is an excellent starting point for choosing a frame size that works for you. Once you know what size frame will fit you, the best way to refine your choice is to test ride a few bikes in that frame size, or a centimetre larger. This will help you determine which is the most comfortable for you.


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