The Greenspeed Magnum boasts a payload capacity of 400 lbs, and with its Aluminum frame it won't break your back lifting it for transport.  In addition, the seat has multiple adjustments, both up and down as well as the back tilting to the angle you need.  The lumbar support is also a nice feature.  To top it off, the Magnum folds for easy transportation.  For complete specs on the manufacturer's website click HERE.