Turkey to Tehran via Trans Asia train no-problem!
 

Just arrived in Tehran from Turkey via Trans Asia train, loaded the bike in Kayseri and unloaded it in Tehran, the carnet was stamped in Tabriz, 140 Turkish Liras for the cargo and 54 Liras for passenger. No problem whatsoever.
There are no ramps in Kayseri or Tehran stations so you have to tip someone (the porters in my case) to help you with the loading/unloading (20 Turkish Liras and 30,000 Rials in my case (5 men), there are no steps to get into both stations, you can use the wheelchair ramp in Tehran on exit.
The station manager in Kayseri is very very helpfful and friendly but u need someone who can translate for you.
I had to to empty the tank but I noticed they dont check it at all and I had a bottle of fuel hidden in my panniers.

Just wanted to confirm that coming via trans asia is possible also the custom manager in Tabriz knew exactly what to do with the carnet and all the rest, probably many others went through the same way.

Now I am in Tehran and its a looong bank holiday here (new year) and all the offices are closed: do I need 3rd party insurance for the bike in Iran? I totally overlooked this as I thought I was going to enter overland (for the same reason I dont have a petrol card but it doesnt seem to be a problem, I could buy petrol for 5,000 Rials per litre, only quantity multiple of 10 litres).

Train?
 

Alex, why did you get the train? Was it because of Snow? I'm travelling up to Dogubayazit leaving Bandar Abbas next week just wondering what the story is. Cheers, Adam

Ride through, no problem.
 

I didnt want to risk to get stuck in this season as the weather was uncertain but at the end turned out to be really good and it can only improve as summer is approaching. Not much snow and the roads as far as I can tell were clean. Knowing this before I would have ridden through actually.

"do I need 3rd party insurance for the bike in Iran?"

Before I was leaving, I learnt that (to my surprise!) Iran is a part of the Green Card system, so most European insurances will cover there. Find out, if your insurance is valid in every Green Card country (I even had a list of all countries in the paper that I got from my insurance company, and Iran was listed).

I crossed through the land border near Dogubayazit (Barzagan?) and they werent interested about any insurance, probably would´ve got through even if I didnt have one. It was not asked by the police while in Iran, either, so I dont really know if they officially require it or not. Sure its better to have one, if you happen to have an accident (and beware, there are crazy drivers in Iran!)