Triathlon Bike Sizing

To get your triathlon bike sizing right, it important that you try the bike before you buy it.

All brands and models are different and are aimed at different markets. They also (confusingly) measure the frames differently.

So a 54cm model in one brand can be a slightly different size to a 54cm model in another brand.

A bike is usually sized in centimeters, although sometimes they are just labeled ‘small’, ‘medium’ and ‘large’.

The measure is from the centre of the bottom bracket to somewhere near the top of the seat tube.

This imprecision is due to different, non-standard frame designs nowadays.

To get a rough idea of the size frame you will require:

1. Measure your inside leg in centimetres
2. Multiply this number by 0.65

So if you have an inside leg of 83cm this will equate to 53.3cm (83 x 0.65). As manufactures don’t make such a size you would either go for a 52 or more likely a 54cm.

Your position on the bike needs to be comfortable for the duration that you ride for. Be aware that you might have the bike in the correct position but it could take you a bit of time to get used to this.

If you are being buying a conventional road bike with drop handlebars your fitting should set you up so that can reach the gears and brakes comfortably when on the drop and on the ‘hoods’. While you might spend more time on your ‘hoods’ especially when training, you should be able to use your drops with ease. This may mean asking the shop to change the handles bars to a slightly different design.

There are three key contact points to consider when sizing a triathlon bike.

These revolve around three fixed points – where your hands, feet and backside go.

If you have any questions about getting the right bike fit, then please just ask us.

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Triathlon Bike Sizing - Saddle Height

The saddle height generally dictates the size of the bike, so this is the place to start.

Generally the saddle wouldn’t be at the extreme end (either high or low) of the seat post. If the saddle needs to be right at the top to feel comfortable then you probably need a bigger frame size. If it is right at the bottom then you probably need a smaller frame size.

You want the saddle to be at a height which results in the knee of your ‘straight’ leg to be slightly flexed. So your leg shouldn’t be completely straight, rather at a 10 – 15 degree angle of knee bend. When measuring this your heel should be in a neutral position with the foot flat (parallel to the ground).

When you pedal your hips shouldn’t rock from side to side. If they do your saddle is probably too high.

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Triathlon Bike Sizing - Reach

This is the distance from the saddle to the handlebars, or how far forwards you have to ‘reach’ to put your hands comfortably on the bars.

The amount of reach and drop is affected by how flexible you are in your lower back, hamstrings and hip flexors. If you are not very flexible you will need to have a shorter reach and to have the bars a little higher. This will put you more upright on the bike.

If you want to be comfortable and aerodynamics are not so important then you can also be a bit more upright.

Body proportions can also influence your reach. Some people have very long arms relative to their upper body and have a ‘long’ reach. Others have shorter arms, or a short upper body, relative to leg length. All these and more variations mean that fitting a bike is not a simple or quick calculation.

Reach can be affected by the drop – this is how far up or down your hands go to be placed on the bars.

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Triathlon Bike Sizing - Drop

The drop is the difference between the saddle height and the handlebar height. Handle bars should usually be lower than the saddle, except for a few exceptions. Very small people might end up with the handle bars higher, and those with restricted movement around the hips might find it very uncomfortable reaching down to the handlebars.

How much drop is suitable depends upon your anatomy and also whether your priority is comfort or aerodynamics.

To optimize performance it is a case of getting a balance between comfort and aerodynamics. The lower and narrower you are (through using aerobars), the less your frontal area and the more aerodynamic you will be.

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Summary of Triathlon Bike Sizing

• Ensure that you are fitted correctly for your bike and if possible try it out before you buy.
• The size of the frame of your bike is determined by the measurement from the centre of the bottom bracket to the top of the seat tube.
• Make sure that the saddle height is such that your 'straight' leg is slightly flexed.
• Your handlebars will probably be a little lower than your saddle, and how far forward you reach will depend on how comfortable you want to be versus how aerodynamic you want to be.

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Got a question about your triathlon bike?
Then ask us!

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