Biking the Chief Ladiga Trail 

We would just double the mileage each day and ride back, yes.

There is a place called elevated grounds coffee and bike shop. They will shuttle you for a dollar per mile. I'm assuming you could split that along three or four people.

Camping is permitted only in designated areas, such as campgrounds. It is not permitted to simply camp along the trail. The trail websites should link to the available camping areas.

There is a campground at 7. Mile marker. Just go in and they will come around and get your $.

Leave no trace and it generally isn't an issue to stealth camp.