We have had a few questions over the years of people wanting to cycle in Afghanistan. Our standard answer has been: are you out of your mind? Please don’t do that!
But, of course, somebody has. Here is an excerpt of what he wrote me.
I cycled in Afghanistan for one month and was later captured by government, they thought I was a spy and sent me to jail, finally got deported to Tajikistan. Westerners are being kidnapped and killed every year, please DO NOT travel by bicycle to Afghanistan, since you will bring trouble to your family and your country. Travelers who survive Afghanistan do not do so because they are smart, they were just lucky. Hope you can advice traveler not to travel in Afghanistan by foot or bike. (this conclusion is based on my discussion with Taliban people in prison).
An exception to this basic rule would be cycling in the Wakhan corridor. A good mountain bike, lots of spare parts and mechanic skills and an above-average level of fitness is required.