I've seen the airless tires and tire tube (solid foam) inserts used for another application, and that is for horse drawn show/pleasure carts. Although cart wheels are spoked the construction is a bit different. Generaly the cheaper ones do not use the traditional nippled spokes. However the probelm arises with wheel strength when used with airless tires or the foam airless tubes. A rim with a properly inflated pneumatic tire will withstand far more abuse (potholes, tight turns, uneven terrain, etc) far better and without warping than one equipped with with the airless type. For this reason I would be suspect of using the airless stuff on any of my bikes. Just my 2 cents worth of experience using spoked wheels in another application.

'bent Brian