Road bikes: how to choose the measurements of the frame
Once you’ve chosen your next road bike, in order to avoid pain in the joints, you should choose the size for your frame, a key parameter to achieve maximum comfort. Each size meets the needs of a more or less wide range of rider heights. However, and here comes the confusion, often the size indication varies from one manufacturer to another. In general, it is based on the length of one of the two main tubes (horizontal or vertical) or on the height of the cyclist (or rather on their inner leg size).
International sizes
The manufacturers offer reference sizes which, as with clothing sizes, range from XS to XL and are relative to the height of the rider. Sometimes, just as with clothing, size guidelines are not accurate or standard because, in order to cover production costs, brands cover the widest possible range among their potential customers. In general, an XS corresponds to a height of up to 168 cm, an S to 173 cm, M to 176 cm, L to 179 cm, XL to 183 cm and XXL above 185 cm.
Mathematical size calculation
To be as precise as possible in calculating the size of the frame, you can use a mathematical formula whose results can be compared with the sizes of the road bike frames indicated by the manufacturers. It’s a very simple calculation: the inner leg height multiplied by 0.65. The measurement corresponds to the height of both the DC tube and the horizontal DC, as these two measurements tend to be identical on road bikes. For example, a person who has an inner leg size of 85 cm will get a measurement of 55.25 between sizes M and L.
How do you measure inner leg height?
You should be barefoot with your legs slightly apart and your shoulders and body against the wall. With a pencil, we mark the height of the groin and measure the distance from the ground.
Table for choosing the size of the bicycle
To choose the size of the bike, you can use this table, which takes into account the standard physical values of people.
| Cyclist’s height | Inner leg | Road Bike | |
| 155 – 160 | 69 – 73 | 46 – 48 | |
| 161 – 164 | 74 – 75 | 48 – 50 | |
| 165 – 168 | 76 – 77 | 50 – 51 | |
| 169 – 174 | 78 – 81 | 52 – 53 | |
| 175 – 180 | 82 – 84 | 54 | |
| 181 – 186 | 85 – 88 | 56 | |
| 187 – 192 | 89 – 91 | 58 – 60 |
The height of the road bike seat
By multiplying the size of the inner leg by 0.885 you get the height to adjust the saddle. This height must be applied from the centre of the pedal crank to the saddle. Use this method of calculation when you are already a little familiar with the bike, as this setting will only allow you to touch the ground with your toes.
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Marco Trabucchi
