3 Fundamentals of Correct Bike Size - Specialized Roubaix

The most important dimension is standover. So, what is it? 

Stand-over is the measurement of the height of the bikes top-tube from the ground at its mid point. In the Caad10 example above, J indicates Stand-over. 

Ok, so why is it so important? Simply put, if you are travelling along on your bike and you need to stop in a hurry, you'll have to jump forward, landing on the ground, standing with your legs on each side of the top-tube. Having the correct Stand-over will ensure you do not impact your groin area during this situation. 

How to test it.

When you stand-over the mid point of the bike, with shoes on, you should be able to lift the bike up until there is a 2 cm gap between the tyres and the floor - without the frame coming in contact with your groin.

If you are looking at the best size option based on a geometry chart, measure from inner leg to floor (with shoes on), remove 2cm and test that measurement against the bikes geometry chart. 

2. Reach

Get this one wrong, and your may be in for a world of back pain. Wether that is upper or lower back pain will depend on wether you buy, or are sold, a bike that is too big or too small for you. Buy the correct size bike and your hours of saddle time will actually strengthen your core and back, not hinder it. 

The Reach is the distance your hands project forward to comfortably rest on bars and manipulate the brakes and gears. 

 

How to test it. 

The quickest test of correct reach is to sit in the correct riding position on the bike (a trainer is great for this or if that is available, take the bike for a quick ride or balance against a wall with someone's assistance). 

Sit on the bike in a neutral position with your hands resting on the hoods (illustrated above) and your head in a natural riding position - eyes looking forward. Now look down at the front wheel hub/axel. If the position is correct the bars should block your view of the hub/axel. If you can see the hub/axel in-front of the bars, the bike is too small. If the you can see the hub/axel behind the bars, the bike is too large. 

Stem length obviously plays a role here. However if you are buying a bike from a store, it should be equipped with the correct size stem for the frame. Ideally you should only have to swap stems if you have a particularly long or short torso. 

Your saddle can be moved forward or back on the 'rails' to make small adjustments to your reach outcome. If the bike is the correct size for you, you should not have to move it all the way forward or all the way back,. 

3. Seat Height

Seat height impacts on comfort and performance - correct seat height optimises both. Your seat needs to allow for a efficient and powerful pedal stroke, while maintaining you in a balanced, static and comfortable seated position. 

It is also important to note that the your seat needs to be in the correct position to properly determine your reach (above). 

How to test it.

This is a simple and quick way to ensure a powerful and efficient seat height position. Sitting on your bike, rest your heal on your pedal when it is in the lowest (6 O'clock) position.

You need to check two things now and you will need another person to assist with this. Check that you leg is fully and comfortably extended. At the same time, when viewed from behind, your hips should be level. If required, adjust the seat height to achieve the ideal balance of full leg extension and level hip placement. When this is resolved, returning you foot the usual cleated cycling position should achieve the correct amount of knee bend.

Size Chart

The following chart provides a rule of thumb approach to determine your bike size based on your height. This is a simple approach to a complex situation, but it is accurate in the majority of cases. Of course the length of your limbs is not factored into the table below and long or short limbs or torso can play a big role in determining the right bike size for you. 

 

Your Imperial Height	Your Metric Height	Bike Size Guide
5 feet 1 inches	155 cm	Size - XXS / 46
5 feet 2 inches	157 cm	Size – XXS / 46
5 feet 3 inches	160 cm	Size – XXS / 48
5 feet 4 inches	163 cm	Size – XXS / 48
5 feet 5 inches	165 cm	Size – XS / 50
5 feet 6 inches	168 cm	Size – XS / 50
5 feet 7 inches	170 cm	Size – S / 51
5 feet 8 inches	173 cm	Size – S / 52
5 feet 9 inches	175 cm	Size – M / 53
5 feet 10 inches	178 cm	Size - M / 54
5 feet 11 inches	180 cm	Size – L / 55
6 feet 0 inches	183 cm	Size – L / 56
6 feet 1 inches	185 cm	Size – XL / 57
6 feet 2 inches	188 cm	Size – XL / 58
6 feet 3 inches	191 cm	Size – XXL / 60
6 feet 4 inches	193 cm	Size - XXL / 61
6 feet 5 inches	196 cm	Size – XXL / 63
6 feet 6 inches	199 cm	Size – XXL / 63