1. After Collision
The helmet must be replaced immediately after an impact. The purpose of wearing a helmet is to protect the head from one impact and only once. After an impact, though the helmet seems to be intact, it may have been damaged or cracked inside. It's quite dangerous to ride with a helmet that has been hit once. It is not protective anymore
2. Obvious Damage
If there is noticeable damage on the helmet, such as small cracks, loose belts, parts falling off, etc., it is a necessity to replace it. Only an undamaged helmet can effectively protect you.
3. After Years of Usage
It is recommended that you replace the bike cycle helmets before it becomes too old. The condition of your helmet depends on its times and environment of usage. If your helmet is preserved well, it can be used for 5 years. The old helmet with aging parts and materials is not as good as new helmets, especially when it is stored in a cold or humid environment.
4. Participating in Other Sport
If you are going to participate in a different sport, you need to replace it with a custom cycling helmet that is more suitable for the new activity.
5. Other Reasons
There are many other reasons, for example, sometimes we simply want to replace it with a lighter, more breathable, and well-designed helmet.
6. Size Selection
The size of the helmet is generally 55-59cm. In order to choose the helmet with the right size, you need to measure your maximum head circumference by circling your head with a soft rule at the forehead.