How about a look at the Otto Bock C2000, an off-road wheelchair with rear wheel chain steering.
The C2000 is an outdoor powered wheelchair from German manufacturer Otto Bock. It packs some nice features including an innovative rear wheel chain drive configuration.
Some of the features of the Otto Bock C2000:
• enAble50 drive control.
• Rear wheel chain steering
• Optional front or rear drive
• Seat raising of 40 cm (optional)
• Electrical tilting and back angle adjustment (optional)
• Various footplates for different areas of application/weights
• Carrier included
• Integrated lighting system.
• Load capicity 352 to 440 lbs.
• Climbing ability 22%
• Speed 6, 10, 15 km/h
• Range 60 km