How Dirt Bike Helmets Protect You

A modern day motocross helmet is made up of four key components being:

  • Hard Outer Shell
  • EPS “Expanded Polystyrene foam” Liner
  • Inner Foam Padding
  • Retention Strap – Chin Strap and “D” Rings

The purpose of the hard outer shell is to prevent penetration of the helmet by a pointed object that might otherwise puncture the skull, and to provide structure to the inner liner so it does not disintegrate upon abrasive contact with the ground. This is important because the foams used have very little resistance to penetration and abrasion.

The purpose of the foam liner is to crush during an impact, thereby increasing the distance and period of time over which the head stops and reducing its deceleration.

It is important that the liner in a motorcycle helmet is soft and thick so the head decelerates at a gentle rate as it sinks into it. Unfortunately, there is a limit to how thick the helmet can be for the simple reason that the helmet quickly becomes impractical if the liner is more than 1–2 inches (2.5–5.1 cm) thick.

This implies a limit to how soft the liner can be. If the liner is too soft, the head will crush it completely upon impact without coming to a stop. An ideal helmet liner is stiff enough to decelerate the impacting head to stop in a smooth uniform manner just before it completely crushes the liner and no stiffer.

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