Just come across this as the emissions specification after the recent visit from the ministry on the M3W.

How does this translate into the UK emissions bands for vehicle excise duty (car tax)?

Salcombe

Are you sure you have this right as it must be running on fresh air. For comparison a Prius is 92g/km?

Well...I hope it isn't 384g/km

Does'nt sound right if that equates up to 384 as you say. There is a specification update on the Mogwire site with speeds, weight etc. where this was listed.

It would make the tax disc very expensive, I think there is a mistake somewhere.

The specification on the Mogwire site must be incorrect.

They also list the horsepower as 82 vs the original quoted 120.

It probably won't be very green CO2 wise...motorbike engines, especially large twins don't tend to run as cleanly as car engines. I seem to remember a figure around 260 quoted at one time.

Maybe it's 0.384kg
Wouldn't surprise me if Mogwire had the '.' in the wrong place...

Mogwire does seem a bit tabloid and I am not sure where they get their information from. Phone hacking? Perhaps they should be interviewed by Leveson.

Maybe the Mogwire specification refers to carbon monoxide (CO) emitted rather than (CO2) hence the confusingly low value. Who knows?

Note the difference:
CO = Carbon Monoxide (Fatal gas, data from Mogwire)
CO2 = Carbon Dioxide (global warming gas, data used for Road tax)

The CO2 figures are related to and can be estimated from the Fuel consumtion.

There was a figure published when Clarkson scribbled a brief (positive!) review a couple of months back. Might have been Sunday Times or similar but can't remember. The figure given there was about 214g/Km CO2 or similar. That's the only time I've seen something quoted as far as I can recall - no idea if it was right or is being re-tested / reassessed.

That would still be rather high but would be more consistent with other comments above. I don't think 384 g/Km is possible - that would mean about 16 mpg.