Using this calculator may make your calculations easier:
http://www.chiefdelphi.com/media/papers/3188?langid=2
A normal electric wheelchair, has one 200watt motor on each side and they usually have 10inch wheels and can go at least 5mph. If your wanting 1.15 m/s with 8inch diameter wheels you will only need about 110rpm. However your going to need a gearbox with a very large reduction to accomplish that in most cases, motor dependent.
1.15m/s is definitely not a brisk walking pace( thats only 4km/h) you might be better aiming for about 6-7km/h.
Have you thought about what motors you are going to use and how you are going to interface them to your wheels?