I used this route from Rouen to Le Mans and the old D438 route coming back (D438 is already on BBR). If your not in a rush, enjoy both routes.
If you see radar control signs - there will be a camera within a few kms so slow down and enjoy the countryside and traffic free roads.
If you stay in Le Mans city you can lock the bike up(look for a hotel with safe parking)as the tram system runs out to the race track entrance! Very convinient not to have all your gear to carry around with you and, the trams run until about 01.00AM - so stay for some night racing!
If you stay in Le Mans the Old Town is worth a visit.