Quite a few bikes doing something similar to the sidecar expedition mentioned above. Most skirting the southern edge of the sahara is fairly straightforward in that there are good roads in Niger, a bit of a challenge round Lake Chad but not that hard, roads in Chad are very poor due to large number of massive wash outs and pot holes but hardpacked tracks so easy enough to drive, just slow going. Then in Sudan there is an easy option. there is a tarmac road after crossing the border heading towards Nyala but then most bikes use the railway line from Nyala all the way towards Costi / Khartoum. Whilst vehicles have to slog their way along the soft sand eiter side of the railway line, motorbikes can ride on it between the rails giving a fairly easy ride. Going further north would be much more challenging. Met a French expat in Chad on national service who had a KTM and was going to ride from Ndjamena north through the desert on a bearing, then cross the border near Blima before heading north into algeria near the Algerian / Libyan border. However he had a mate in a LR110 to carry the fuel. Likewise with another traveller on a KTM who did the Agadez - Blima route and other desert travels in Mali but used a local guide with a landcruiser to carry enough fuel. Think if you stay further north it will be down to fuel capacity as to what is possible but could use local guides to carry extra fuel on the long stages. Good luck.