The Dhulikhel to the Tibetan Border route, along the Araniko Highway, is 83 kilometers long and takes 2 days to complete. On the first day, ride from Dhulikhel to Dolalghat via the Paanchkhal valley. Then cross bridge over the Indrawati River and head towards Lamosangu, where you can make an overnight stay. Lamosangu is at the turnoff to Jiri and is 27 kilometers away from Dolalghat.
Then proceed to Tatopani via Barabise. From Barabise, the road condition is not that good although this is part of the strategic highway. After riding for around 23 kilometers from Barabise, you reach Tatopani and further 4 kilometers to Kodari, the Friendship Bridge. You can make your overnight accommodation in Tatopani or ride back to Borderlands which is around 6 kilometers downhill from the border. If you stay in Tatopani, you could enjoy the hot spring.
On returning, you could follow the same trial to Dulikhel or Kathmandu or ride on a bus with your bicycle.
Read the Mountain Biking Routes for exploring other biking routes in Nepal.