Buying a Full Size Bike
Buying the right size bike is extremely important as the wrong size bike can be dangerous, uncomfortable and an expensive mistake. Riding the wrong size bike can have the following disadvantages:
- Cause pain and/or injury
- Inhibit pedalling technique that can result in you being less efficient
- Is less comfortable and therefore less enjoyable
The table below is a general guideline of the sizes for both Mountain and Road bikes. There are various brands that have different size frames, so for accurate results please ask a professional at any bike store.
Bike Size Chart
Road bike frame size (cm)
Mountain bike frame size (inches)
The size of the bike is measured from the centre of the chainset (the object the pedal arms are attached to) to the top of the frame at the point where the seat post is inserted. Unfortunately some manufacturers measure their models to the centre of the intersection of the top tube and the seat tube, which can distort some of the sizing a little. The following rules of thumb should be applied when you try a bike for size.
Choosing The Right Size Bike
|BMX Bike||One standard size applies to all|
|Hybrid Bike||Standing flat-footed on the ground, you should have a minimum of 2.5cm clearance between yourself and the top tube of the frame|
|Mountain Bikes||Standing flat-footed on the ground, you should have a minimum of 5cm clearance between yourself and the top tube of the frame|
|Road Bike||Standing flat-footed on the ground, you should have a minimum of 2.5cm clearance between yourself and the top tube of the frame|
If you are not able to physically measure the size yourself, the simple calculation below can be used to estimate your required frame size.
- Take your inside leg measurement to the floor
- Subtract 5cm for mountain bikes, or 2.5cm for road bikes
- Subtract 23cm, the average distance from the bottom bracket to the ground
Using these rules will give you the maximum frame size that you will need.
Keep in mind, buying a bike of the correct size is not just about the correct height measurement. As bikes get taller height-wise, they also get longer. The distance from the seat to the handlebars increases, on average, by 2.5cm for every 5cm increment in frame size. Therefore, while you may be able to stand astride a taller framed bike, you must also ensure that you can still comfortably reach the handlebars and manage all the controls. Remember that the seats on all bikes are adjustable by between 10cm and 25cm so the bike can be tailored to fit you.
As we are all built to different shapes, finding the right size bike and getting the right position set up on the bike can be quite difficult. The above information should start you off in the right direction, however advice from a professional who can physically see you on the bike and adjust your position is best.
Having the right size bike and the right position is more important if you are doing long rides (30ks plus) and if you are buying a racing bike. Problems created from a poor position on the bike may be amplified the longer a person is on the bike.
As mountain bikes have a more upright, comfortable position, the ideal position is not as critical. This is why three or four adult sizes can cater for the majority of the population. In contrast, as race bikes demand a less comfortable and more efficient position, the perfect size and position is much more important and is the reason why the size of race bikes can vary by centimetres.
Lastly, buy a good brand. Although what brand you buy often comes down to your budget, the better brand bikes generally have increased performance, are safer and are more durable.
It is recommended that someone who is doing long rides or riding race bikes be fitted by a professional. To find a bike shop in your area click here.