Meanwhile pretty touristy with all the negative aspects (begging children...). But the view of Everest's north face from close up is absolutely rewarding! Lots of organized bike groups like on the Friendship highway.
Since April 2008 it has become impossible to enter Tibet individually. That is when mainly the checkpoint have been reinforced with army personal. Because of that it is no more possible to enter without permit as it used to be for many years. This applies for the whole of the TAR.
There are at least 3 different routes you can cycle from the Friendship Highway (318) to Everest Base camp.
Everest Base Camp
Officially it is not allowed to go higher up then base camp (fine 200$). But the controlling officer leaves the place at the end of the saison (mid of october).The route from base camp (5170m) to the advanced base camp (5460m), Camp 1 (5500m), Camp 2 (5940m) to Camp 3 (6300m) is an easy walk mostly over a moraine. The route is easy to find, the only point where you have to be careful is at about 5650m. Here you have to go left onto the middle moraine. Very rewarding is the part just below Camp 2 where you walk past the very impressive seracs of the Rongbuk glacier and see the summit ahead.
Pelbar - Pedruk - Rongbuk
This is the main route. Used to be a good road but because there are so many Land cruisers the surface has become very bumpy (washboard). Cycling over Pang La (5205m) is great. From the north there are 900m to climb in 41 switch banks. From the south it is 1000m in 64(!) switch banks. Atop there are great views of the Himalaya: Makalu, Lhotse, Everest, Cho Oyu!
Old Dingri - Lamar La - Pedruk - Rongbuk
The climb from Digri to Lamar La pass is quite good. But the road down towards Pedruk is rough with many river crossings - wet feet guaranteed! Quite some Tourist Land cruisers on the road.
Old Tingri - Lamna La - Chopuk - Rongbuk
This pass I have only cycled partly. There is much less traffic here, but the Land Cruisers do it also. Supposed to have great view from the pass.
Do not climb above base camp if you are not well acclimatised!
ABC Camp : N28° 06.3337 E086° 52.2786
Camp 1 : N28° 06.0217 E086° 53.0535
below Camp 2: N28° 05.0006 E086° 55.1561