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.

Disclosed is a folding wheelchair having a plurality of support members each having a first and a second end, a first separation distance measured between the respective first ends of a second support member and a fourth support member, a second separation distance measured between the respective second ends of the second support member and a fourth support member, a third separation distance measured between the respective first ends of the first support member and the third support member, wherein the wheelchair can be disposed in an open position and a folded position and, in the open position, the first separation distance is shorter than the second separation distance, the first separation distance is shorter than the third separation distance, and the second separation distance is shorter than the third separation distance. An intersection angle of the second and fifth support members is less than 55 degrees.