i was with my friend for his first fixed off-road voyage this weekend. he is a very skilled rider and rides fixed road a ton but i was impressed at how fast and fluid he rode.
i expected to catch him on every downhill... NEVER... he cleaend the whole f@ckin skills trail (middle run, de for those who know), REEEE-DICULOUS. i can't ride that **** on my bike.
if you can ride, you can ride trails fixed. i just don't know that i can ride (like that)....
i believe he was running 34x18 on 29" wheels (slightly higher than his usual raio). as soon as it pointed up he was gone.
on more technical track it might not be so ideal, but in smooth singletrack with lots of rollers it appears to work just fine!
oh and i never saw him lock up the rear tire once (front disk).