Is there an official reason why Denis Menchov fell off on a straight road in the final TT? Was it mechanical failure, puncture or something else?

 he knew he had it in the bag, so he wanted to add to the drama........you know make the win more memorible.  to bad that sastre couldnt pull in a 3rd place finish though

Its not that simple....have you ever been on Roman cobbles in the rain?  I spent a few months living near rome and those things are slippery when try, in the wet they can be hazardous to walk on...even cars spin their wheels on them!  They're a very smooth stone, much more smooth than cobbles in Belgium that I saw....very dangerous!

 You're talking about a rider who also fell going up hill last year in the Tour.  ?!?!?

Looks like he started to wobble just before he went down. Maybe like a speed wobble on a motor bike - he was probably pushing 60 km/h at the time. Could also have been the famous tifosi - conspiracy theory anyone?

I think he just knew he had the Giro win in the bag and was close enough for the stage win as well that he gunned it, knowing he was indeed on a straight. Thing is, the increase in pedal force was enough to throw him off when he hit either an oil slick or an unusually placed cobble. Combination of the rain and cobbles with perhaps a bit of throwing caution to the wind imho.

roman cobbles are slippery as hell.

hope on a plane to rome, wait until it rains, then bike over those roads at high speed.

Those stones are not perfectly flat.  Some are at angles in relationship to each other.  It is a crummy surface to cycle when wet.  He certainly had the wettest ride.  The man was humping.  Even with the fall he had a great time.  I admire the guy a lot.

 The bumpy surface was evident (to me anyway) when when his front end was bouncing around. And it did bounce from a bump (the wet surface didn't help the situation) right before his bike slid out out from under him.

Front wheel slip on wet cobbles, as simple as that. I found the TT to be extremely dangerous, even in dry conditions. Too many cobble passages and bends. If Menchov would have lost the Giro because of that accident it would have been a huge shame on the Giro responsibles, imho.

I think it's a combination of reasons.

It doesn't rain a lot and there is a lot of traffic in Rome. Traffic means waisted rubber of all the tires on the pavement which will be there until the next rainshowers. When the rain comes this rubber becomes very slippery. And of course, the cobblestones aren't flat.

So this wet, rubbered and cobblestoned pavement becomes a very dangerous enemy for the TT.

Hammering the bike gives power and pressure on the wheels which doesn't help you staying strait as well.

It amazed me that everyone else stayed on the bike. Tell's this something about Menchov....;-)

The only question I have is did Menchov give all his $$ winnings to that tech monkey who jumped out of the car and had Menchov on a new bike within seconds. That guy won the race!!!