So I built up the Airborne mtb as a singlespeed, using a Surly chain tensioner.  34x16 was overgeared for the orange trail at LewisMorris, nearly killed myself.  And the tires were tiny. Now it's sporting 2.25x26" tires and 34x17 gearing.  I have an 18t cog if needed.

However, the upshot was I took the old tires, put them on my spare 26" rims (old ones due to be replaced when I get the $) and put them on my Raleigh 29er.

Let me say, i like the 29er.  It rides over stuff real good.  The tires are cushy.  But i admit what others have said is true... it is long.

With 26" rims and 1.95" wide tires, the 29er bb is only 3.4 of an inch lower than the bb on my Airborne which is intended for 26" rims.  And the frame, looked at from axle to axle, is only about 1" longer than a 26" frame.

It rides okay around town.  I'm betting with bigger tires, or maybe 650b wheels, it'd be a kick @ss mountain bike. (or I could go back to 29s).