OT: I want an OX

So that's also the last LandRover engine

Steel frame ladder chassis and 2wd ... like the original LandRover.

Hmm. The pneumatic tyre first appeared on bicycles. With no suspension. I'm willing to bet one of the reasons was lower friction.

The chassis is a steel/wood laminate.

But suspension owes more to a 2CV than Land Rover.

I think comfort (and not shaking the thing apart) was the original reason, but they'll have found the efficiency thing quite quickly. Mr Cheerful's own link showed that pneumatic tyres are more efficient than solid - he just didn't quote the relevant lines.

Surely it's not that simple?

Define the characteristics of each tyre, and the characteristics of the surface the tyre is being tested on, then compare.

For example, the solid tyre could be one metre in diameter, 10mm wide, made of a very hard substance, have a triangular section, operated on a perfectly flat hard surface, and be carrying an insignificant load. I'm pretty sure that under those circumstances the rolling resistance would be less than an average car tyre.

Chris

But how long would that narrow contact footprint remain narrow?

Large wheels may not be a good idea anyway. The axle/suspension may intrude on the load space - or make it higher than necessary.

The fact is the only place you see solid tyres is on things like a forklift designed to never leave the smooth factory floor.

"Operated on a perfectly flat hard surface" is about the only place solid tyres win. And I have said that several times in this thread already.