3 Fundamentals of Correct Bike Size

Road Bike Size / Fit Basics

Before you purchase your new road bike, you need to ensure the frame meets 3 basic size requirements - Stand-over, Reach, Seat height. 

1. Stand-over

No dimension is more important than Stand-over. But what is stand-over you ask?

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 have 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. 

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 your back. 

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). 

When you are sitting in a neutral position with your hands resting on the hoods (illustrated above). Sit on the bike with you 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.

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, rent 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. 

 

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