A wheelchair having an emergency brake system in which a wheel of the wheelchair has a hub, a rim, spokes extending between the hub and rim, and a rod extending between the hub and rim. A helical spring surrounds the rod, with a fixed end attached to the hub and a free end movable along the longitudinal direction of the rod. A brake mass structure is attached to the free end of the helical spring and includes a pin structure. A main frame connects to the hub of the wheel. An extension structure extends from the main frame and includes a spacing segment and a hook segment having a groove configured to engage with the pin structure. At a speed threshold, the pin structure engages the groove of the hook segment to prevent acceleration of the wheelchair.