Bike Size Guide

Buying a bike which is the right size is probably the most important part of choosing your new cycle.  But how do you work out what size to get?  With this guide we hope to shed some light on the subject…

Children’s Bikes

If the bike is for a child, they generally fall into age categories based on the average size of a child of a specific age.

There is no hard and fast rule that says that you must buy a bike of a particular size for a child of a specific age.

If the child is comfortable and not too stretched on the bike, and they can manage all the controls and turn the handlebars safely, reach the brake levers and operate them and touch the floor with the ball of their foot, then there is nothing to prevent you from selecting a bike in a bigger age category.

Suggested Sizes

12″ Wheel Cycles – Suitable for ages 2½ to 4.
14″ Wheel Cycles – Suitable for ages 3 to 5.
16″ Wheel Cycles – Suitable for ages 5 to 7.
20″ Wheel Cycles – Suitable for ages 7 to 9.
24″ Wheel Cycles – Suitable for ages 9 to 11.
26″+ Wheel Cycles – Suitable for ages 11+ (These are classed as adult cycles).

First Bikes: 12″ & 14″ wheels, suitable for average ages 2½ up to 5.  Larger and slightly older children should benefit from the 14″ wheel bicycles.

Once a child has learnt to ride without stabilisers (generally about age 5) they will move up to a 16″ wheel cycle.  These do not normally come fitted with stabilisers but they can be added to virtually all 16″ wheel bikes.

Once you get into the realms of 20″ wheel bikes and above, you may be offered multiple frame sizes. This has the benefit of being able to fit a younger child onto a bigger wheeled bike if they are confident riders. Although you will find that size options are generally not offered on a particular model, rather that different models have different frame sizes.

It is a very tempting thing to do, but don’t buy a bike which is too big for your child in the hope that they will grow into it. They will, but in the meantime they will be riding a bike which is not easy for them to control, which can be very dangerous. It does not really save money anyway, because if you change bikes more often, the outgrown ones will have a higher resale value.

Adult Bikes

Once you are reach adult bikes (26”, 650b, 700c & 29er), then size is only determined by frame size. The size of the frame is measured from the top of the frame at the point where the seat post is inserted, down to the centre of the axle carrying the pedal arms (bottom bracket) .

The majority of adult dual suspension bikes are 26″ wheel with a 18″ or 19″ frame, this can also be referred to as Adult or Uni-size. Modern dual suspension “Y” frames provide more clearance and can fit a wider range of riders, starting at around 5′ 2″ up to 6′. This is achieved by adjusting the saddle height.

The following rules of thumb should be applied when you try a bike for size:

Bikes to be used on roads and paved surfaces: Standing flat footed on the ground, you should have a minimum of 1″ of clearance between yourself and the top tube of the frame. The same rule also applies to gents traditional bikes.

Off road bikes: Standing flat footed on the ground, you should have a minimum of 3″ of clearance between yourself and the top tube of the frame.

For ladies bikes, or bikes with a low step over frame, you should use an imaginary top tube, as even though you may be able to stand over the bike, frames get longer as they get taller.

A simple calculation can be used to estimate your required frame size if you are not able to sit astride a bike to measure:

Measure your inside leg measurement to the floor, subtract 3″ (for mountain bikes, or 1″ for road bikes) then subtract 10″ (the average distance from the bottom bracket to the ground). This will give you the maximum frame size that you will need.

But buying a bike of the correct size is not just about the height from the ground. As bikes get bigger height-wise, they also get longer. The distance from the saddle to the handle bars increases by on average 1″ for every 2″ increment in frame size. So you must also make sure that though you may be able to stand astride a bigger framed bike, that you can still comfortably reach the handlebars and manage all the controls. Remember that the saddles on all bikes are adjustable by between 4″ and 10″ so any bike can be tailored to fit you perfectly.

Please note: Cycles with suspension seat posts will effectively add up to to 2 inches to the frame size. For this reason you should choose a smaller frame size to avoid an oversize bike (ie. select a 19 or 20 inch frame rather than 21 inch if it comes with a suspension seat post)