As it says, how can I tell what trail a set of 29er Rebas have – did it change with the year or was it available in different trail within a year.

I think they're either 07 or 08 models if that helps. They don't have powerbulges like I think the 09 ones do.

I might have misunderstood but is 'trail' the distance from extended fork line to actual contact patch of the tyre? If so doesn't it depend on the head angle/tyre type/pressure and fork travel? Should be easy to measure.
If not WTF is 'trail'?

Jam, yes, that's right and it does depend on all the factors you
mentioned but forks have a 'nominal' trail measurement and 29er forks have recently increased it to give faster handling I believe.

FWIW I've got a set of 2007 SLs and 2010 Teams – both set to 100mm. The teams seem to handle snappier but I guess this could be for a number of reasons. Sorry I'm no help

it's "offset" that changed with the rebas, older versions were 38mm new are 47mm. It makes the steering faster to correct the old "29ers handle like barges" complaints. Different bike/frame designs will benefit more than others with a larger offset. From memory it was 2008 models onwards that had the 47mm

51mm on my Fisher

Stop worrying Clubber – I'm sure I've met you and I'm sure it was you riding the tandem solo from the back seat. A 29er is going to be too small for you – get the next wheel size up.

Jam29er is that with the fisher G2 fork set up?

Ah yes, offset is really what I meant, isn't it 🙄

igm – yes, that was me at SSEC – it was a bit of a stretch though 🙂

Any suggestions as to how I'd know for sure if it's a 2007 or 2008 model?

If there's no power bulge it'll be a 38mm offset.

So it's only the latest model (eg 2009+) of Rebas that have the increased offset?