Air-Powered Motorbikes: Fact or Fiction?

Yes. And very low in comparison to other methods.

What about the economy? Can we replace diesel/petrol at all by this method?

Yes. Not economically. The Laws of Thermodynamics get in the way:

• 'You can only lose'
• 'You can't even draw'
• 'This is the only game in town'

(with apologies to Stirling Stan in this forum).

Air motors are pretty efficient. The problem is gonna be that 10 m² tank strapped to the back.

where does the pressurized air come from, oh, you run a 40% diesel generator to make electricity at 95% eff, to run an 75% efficicent air compressor, that fills a tank to run a 65% efficient air motor. so net 18% efficient.

Two links

http://pesn.com/2006/05/11/9500269_Engineair_Compressed-Air_Motor/

and http://www.engineair.com.au

Compressed air hybrids are running now - comming soon to a European car Near You

I found a picture of this beast and I was wrong about the big tank. Apparently this uses high-pressure (maybe 3000 psi) SCUBA tanks for a range of possibly 10-20 km. And this is a lot closer to a moped than a motorcycle. So, it looks like it works OK. I'd have some safety concerns about giving every Tom, Dick and Harry a high pressure carbon-fiber tank and I'd worry about refill times unless I lived near a lot of SCUBA shops, but it's basically OK. I guess my question would be why not just use a battery powered one? It would be a little more efficient.