Oooh, this is exciting.
Tibet is huge. It's almost as big as Alaska, which is only bigger by an area equivalent to Norway's.
I've included photographs of a map below, just to give you a slight impression of the geography.
As with Nepal, we'll be staying in hotels and lodges reserved by Asian Trails.
Hotels
Kyichu Hotel, Lhasa
Map of Tibet
To get from Kathmandu to Lhasa, we'll be traveling along the Friendship Highway.
The Friendship Highway
The Friendship Highway goes from Kathmandu to Lhasa in Tibet, and that's the route we're following into Tibet. (Kathmandu is near the lower left corner, Lhasa in the upper right)
While it isn't easy to see, there are several high passes along the route, three above 5000 meters (16400+ feet). Fortunately for us, most of the time we'll be at around 4000 m or below, so we'll probably only be miserable for a couple of days.
My Lonely Planet guide to China has the friendly advice that travellers don't use Tibet as their training ground for long-distance cycling. I'll keep that in mind.