A few years ago, I had an old 60's type Moulton with steel 16" x 1 3/8 wheels (sorry I don't know the modern metric sizing). I fitted it with the cheapest tubes and tyres - Halfords own brand, I think. A feature of these rims and tyres was the difficulty of fitting the beading over the rim. I broke several resin tyre levers, and generally had to resort to strong arm tactics to force the beading over the rim. However, the knock on effect of this was that I could blow the tyre's up rock hard, with no risk of forcing the tyres off the rim. Although the energy saving due to low rolling resistance was probably more than made up for by the extra work involved in trying to get the last bit of air into the tyres. IIRC, I used to get these up to around 90 to 100 psi.