Hi there,
We camped at BSJ last year and we found that to get to the circuit you were quicker walking that waiting on the bus (this is the bus to the circuit from the front of BSJ to the entrance at KN). Especially coming back, and if you don't like confined spaces and being wedged into peoples sweaty pits then I would recommend walking as the bus gets very busy during the race.
To get a bus into Le Mans town centre from BSJ your best bet is to walk along to Arnage (which will take you about 20 mins) and get the bus from the high street, they go every 15-20 mins, and the bus stop is right next to a bar so you can sit and have a beer while you wait. We used this to get to the drivers parade on the Friday and were very impressed with the service, it wasn't too busy either.
What day are you arriving on BSJ, our lot will be there from Thursday evening till Monday morning. If you mention some defining characteristic of your campsite then i will drop by to say hello. BSJ is massive so be specific, the campsite with the blue tent won't quite do it.
Jay
Jay