I just cycled The Loop a few days ago. Just hop on anywhere, don't worry about maps. It's extremely well signed with excellent pavement. I don't think I went much more than five miles without seeing a water fountain and bathroom.

It wasn't easy finding the distance of the basic loop. Tucson brags that it's 130 miles long, but that includes spurs and both sides of waterways in many cases. It's actually just over 50 miles. Total elevation gain about 1000'.