Geoff Apps of Cleland fame runs wide tyre on narrow rims at low pressure and swears they are great off road. This is contrary to the idea of wide tyres on wide rims for off road but Geoff has been riding off road longer than any of us so maybe he has a point. Read his blog its interesting.
I own six 1980's 'Cleland style' bikes including:
*Three made by Cleland (26mm rims & 47mm or 54mm wide tyres)
*One made by Cleland and later upgraded by Highpath (22mm rims & 54mm wide tyres)
*One made by Highpath (22mm rims & 54mm wide tyres)
*One made by Jeremy Torr's company - English Cycles (30mm rims and 26.125" tyres.
The Highpath bikes are the most agile and the English Cycles' bike the least.
Geoff Apps' choice of narrow rims/wide tyre combinations came from his motorbike trials background were this was and remains the norm.
On a bicycle, the lateral stability of a wide tyre is dependent on the characteristics of the chosen tyre; the width of the inner-tube, and the tyre pressure. The idea is that instead of ricocheting off obstacles, a tyre on a narrow rim is more likely to snake around them. This means that you can ride over house-bricks etc and still have total control over the bike's steering and balance. Though not so good for doing 'tail-slides' etc.
So that all of the air pressure supports the tyres wall, it is important that the uninflated width of the inner-tube is the same as that of the tyre.
Apps also uses low tyre pressures (around 5 to 20 psi). It is therefore important to frequently monitor the pressures. If they drop too low the tyre wall will not be supported enough and the tyre will become laterally unstable.