Took part in the Banjul Challenge in January this year. Crossed from Mauritania into Senegal via Diama Dam, travelling south. We were in a bunch of clapped out 2 wheel drive cars and had no bother with the route. Can't give you any directions as can't remember any landmarks. The road from St. Louis to Diama is short and good, but from Diama to the N2 in Mauritania must be 60 miles over mud roads. These were quite rutted in places but dry so passable with care. I guess a road bike will have no trouble if you take care. The biggest problems will be finding the correct route through all the tracks.