For a helmet to do its job, which is to absorb and dissipate collision energy, it must fit correctly by conforming to the size and shape of your head. Do not make the mistake of selecting a helmet because it matches your hat size or by guessing at small, medium or large remember that one manufacturer’s small may be a larger small than another manufacturer’s. You must always take time to try on the helmet to be sure of a proper fit.
As a starting point, try on several sizes of various helmets from different makers. You will probably notice that one company’s helmet feels more comfortable than others. Part of the reason for this is that some helmets are more oval-shaped and another’s are more round-shaped. The shape of your head which certainly differs from person to person will determine which is best for you.
To be effective, a helmet must fit as snugly as possible without being too tight; that is, not so tight that it causes discomfort or headaches. It should sink down completely until the “roof” contacts the top of your head. It should also be in contact with all parts of your head. This is the critical factor if the helmet is to work effectively in a crash.
If a helmet fits loosely several things can happen: The helmet may move around on your head; it may lift due to wind forces; it can be too noisy; and in some cases it may even come off in a crash. Imagine what happens in a sudden and violent impact if there is any space between the helmet and your head: When the helmet stops abruptly on impact it allows your head to accelerate inside the helmet however instantaneous it might seem which increases the force delivered to your head.
After trying on a helmet for a few moments, take it off and look for red spots on your forehead that indicate uncomfortable pressure points. You might want to wear the helmet in the store for a few minutes to make sure that it is as snug as it can be without causing any aches. If it fits correctly, your skin should move as the helmet is moved, and you should feel an even pressure on all parts of your head. Also keep in mind that a helmet will loosen slightly with time, therefore when new it should fit as snugly as you can comfortably wear it.
If you are considering a half-head, pay very special attention to whether you can remove the helmet with the strap attached. It has been found that in some collisions, the helmet twists forward or backward so severely that it either exposes part of the skull to injury or even comes off! With the strap securely fastened, try to forcibly rotate the helmet in all directions, especially front-to-back. If you can remove the helmet with the strap attached, it’s no good. And never attach the strap loosely for reasons such as to make it easy to remove after a long ride, as this defeats the purpose of wearing the helmet.
A helmet can save your life. It is an important investment, so be sure to choose one that fits correctly and securely.