The deck of a treadmill is the main bottom part that holds the rollers that the belt travels around. The longer the belt, the longer and stronger the deck needs to be.
Which Kind of Deck Do I Need?
Decks are made of wood of one form or another. As the belt length and price of treadmill increase, the deck material may typically goes from a thin particleboard to a thicker and stronger medium-density fiberboard. Typically, this progression is from ¾” thick to 1” thick. As a very heavy person on a thin deck can crack the deck, the strength of the deck is one of the main factors manufacturers use to determine the user weight capacity of the treadmill. Decks should flex, but not too much. See the following illustration:
Decks are coated with a laminate to protect them from wear and decay. Some manufacturers coat only one side of the deck, but coating both sides is better, in order to avoid warping to the side that has the laminate.
Of course, treadmill manufactures know all this and few treadmill buyers do. However, buyers can avoid these details by paying attention to the user weight capacity and belt size of a treadmill. Higher weight capacities and longer belts almost invariably mean better decks.